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CHEMISTRY

Year 11

Revision Work Book

The Chemical Earth (Syllabus Topic 8.2)

Chemistry is the study of matter, i.e. anything which occupies space and has mass. So in this course, you will start by revising concepts of the types of matter, the particle theory and atomic structure in the context of the Chemistry of the Earth. The living and non-living components of the Earth contain mixtures of thousands of chemicals, from which we separate out those we find useful.

MIXTURES and SEPARATIONS

Mixtures

A mixture consists of two or more different substances together in any proportion. The substances in a mixture can be elements, compounds, or both elements and compounds. This means that the particles in a mixture are not all the same whereas in a pure substance the particles are the same. We can use diagrams to show this.

Matter

Pure Substances Mixtures Elements e.g. oxygen, iron, mercury e.g. air, soil, blood, rocks

Compounds e.g. acids, bases, salts solutions, alloys,

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1 element A mixture of 3 different elements

Another element

1 compound A mixture of 2 different compounds

Another compound A mixture of 2 elements & 2 compou • The composition of a mixture can vary. For example, the mixture air is still air even if it contains more than the usual amounts of components such as carbon dioxide or water vapour.

• The substances in a mixture are NOT chemically combined together in a fixed ratio by weight; as they are in a pure sample of a compound. They can usually be separated easily by physical methods such as evaporation, decanting, or using a magnet. • Substances in a mixture can usually be separated easily by physical methods such as evaporation, decanting or using a magnet. Question 1. Use the following symbols to show the structure of the substances listed below.

Symbols: Hydrogen Oxygen Sodium Substances: a) hydrogen gas b) oxygen gas c) water d) sodium hydride e) sodium oxide e) sodium Question 2. Complete the following table to show differences between a mixture, an element and a compound. Mixture Element Compound Composition varies Particles all the same Components not combined in a fixed ratio

Components separated by a chemical reaction

Mixtures of elements and compounds are present in all parts of the Earth, they are found in the:

• Biosphere – the living things of the Earth • Lithosphere – the earth’s solid outer mantle and crust • Hydrosphere – the earth’s water • Atmosphere – the mixture of gases surrounding the Earth.

Many of these mixtures can be used as they are, without the need for separation procedures. In Australia, we use many mixtures from each of these zones in this way. Question 3.Complete the following table to show uses of some mixtures: Zone Mixture present Use Biosphere Wood and coal

Manure Fruit, vegetables, meat

Lithosphere Gemstones Sand Sandstone, slate Granite

Hydrosphere Fresh water

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Atmosphere Air

However, many mixtures do need to be separated into their components (parts) so that we can use them effectively. Question 4. Complete the following table to show substances extracted from the mixtures listed and a use of each substance: Zone Mixture present Substance

extracted Use

Biosphere Sugar cane Plant tissues

Lithosphere Metal ores e.g. Galena Sphalerite Bauxite

Hydrosphere Salt water

Atmosphere Air

Separation of Mixtures

Deciding Separation Procedures The procedures used to separate the component (parts) of a mixture will depend on:

• What is in the mixture – the number of components and the properties of each of these. Some examples: a) If you wish to separate two substances and only one is soluble in water, you can add water and filter off the insoluble substance, which will have particles too large to go through the pores in the filter paper. The soluble substance can be crystallised from the filtrate. b) To remove broken pieces of sea shell (calcium carbonate) from sand (silicon dioxide), you could use their different chemical properties. Calcium carbonate reacts with dilute hydrochloric acid whereas sand does not.

c) To separate substances with different boiling points, fractional distillation would be a suitable technique, the substance with lower boiling point turning to a vapour first.

• How pure the products need to be e.g. copper must be 99.9% pure to conduct electricity efficiently.

• Economic issues such as the energy needed for the separation process & the costs of building the

separation plant and any equipment used. • The states of the components of the mixture:

States being separated Process used Examples Solids of different sizes Sieving Sand from gravel

Weed from crop seeds Flour from wheat germ

Solids and liquids Filtering or Decanting Perhaps centrifuge first to pack down solids

Sediment from wine Solids from liquid sewage Cells from blood

Solids dissolved in liquids

Evaporation then condensation Salts and fresh water from sea water Sugar crystals from syrup

Liquids Fractional distillation Petroleum products from crude oil Alcohol from fermentation mixture

Gases Liquefaction Nitrogen and oxygen from air Gravimetric analysis

Gravimaffectsuses fo You mconten Questimixturea) etha b) sand c) a sol

Gravimetric analysis is a method of chemical analysis involving the measurement of the masses of substances used in, and produced by, a chemicalreaction

etric analysis provides useful information on the mineral content of ores. The relative purity of an ore decisions about whether or not it will be economic to mine an ore and extract the metals present. Other r gravimetric analysis include finding the salinity of water and the level of pesticide residues in soil.

ay have carried out experiments in class using gravimetric analysis to find such things as the moisture t of barium chloride crystals or the salt content of a sample of salt water.

on 5. Draw fully labeled diagrams to show the apparatus you would use to separate the following s in the laboratory.

nol and water (to recover both substances)

and a solution of copper sulfate (to recover both)

ution of copper sulfate (to recover the copper sulfate crystals only)

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Question 6. Describe how you could separate the following mixtures. For each mixture, state the property you are using to bring about the separation. a) iron filings and sulfur b) sand and salt c) crushed egg shells (calcium carbonate) and sand. Question 7. Describe an experiment you performed in the laboratory which uses the technique of gravimetric analysis. An Industrial Separation There are many separation processes used in industry. The one to be described here as an example is froth flotation. This is a separation technique used to separate mineral ores, mainly lead, zinc and copper sulfides, from the waste material (gangue) with which they are associated in the earth. This technique uses the different surface tension properties of mineral ores and gangue. The Mixture being separated: Australia has more than 20% of the known lead-zinc resources in the World and is the largest exporter of these metals. Lead/zinc deposits are found in places such as Hellyer and Rosebury (Tasmania), Mt Isa (Queensland) and Broken Hill (N.S.W.). In these deposits the lead and zinc are present as the compounds lead sulfide (in the mineral galena) and zinc sulfide (in the mineral sphalerite) mixed with other minerals, which are not economically useful. These waste minerals are called gangue. The mined ore is first crushed and ground into small particles, and then froth flotation is carried out. During froth flotation, the crushed ore is mixed with water in a large tank, chemicals are added, the mixture is stirred and air is blown through the tank. The chemicals make the ore minerals stick to air bubbles, which float to the surface The metal sulfides float to the top in the froth and are skimmed off. Gangue particles fall to the bottom of the tank and are removed. The lead and zinc sulfides are filtered from the water and chemicals, which are re-used. To obtain lead and zinc metals from the sulfide compounds, chemical reactions are needed. They are heated with coke in a furnace. This process is called smelting. Products of Separation and their uses: Lead is used:

• in lead-acid batteries • in crystal glassware • to protect chemical plants from strong acids (it is unreactive) • as flashing to stop water entering buildings (it is insoluble) • as a protective barrier against radiation and noise, as sheeting and as a glass additive in computer and

TV screens (it has a high density) • as an alloy.

Zinc is used: • to protect steel from corrosion by galvanizing (it coats the iron and when the coating is broken it reacts

in preference to the iron). Corrugated iron is actually galvanized steel. • die-casting of metal parts • to make alloys such as brass which resist corrosion • in dry cell battery cases • as zinc oxide it is used in plastics, rubber products, paints, cosmetics, sunscreen and medicines.

Wastes: Gangue may be taken to a tailings dam, where the water is allowed to evaporate. It may eventually be used to fill mines after they are no longer being used. It is important that water polluted with chemicals must not be allowed to enter local streams or enter the food chain. If more economical or more efficient methods are discovered to extract minerals at lower concentrations, tailings may again be treated to obtain any remaining metal. Impact of the separation: Without this separation process it would not be possible to efficiently extract the metal required. In the early 1900’s, extraction of zinc ore was very slow until it was discovered that adding eucalyptus oil to the crushed rock during froth flotation allowed the separation of zinc sulfide from lead sulfide.

PURE SUBSTANCES

Pure substances are ones in which all the particles are the same.

If the particles are made of only one atom, or if all the atoms within each particle are the same, then the substance is an element.

If the particles contain different atoms joined together, then the substance is a compound.

Pure Substances

Elements Compounds Metals Semi-metals Non-metals Organic Inorganic E.g. copper E.g. silicon E.g. sulfur E.g. hydrocarbons, E.g. acids, aluminium germanium hydrogen alcohols, esters bases, salts Compounds are classified into groups based on their common chemical characteristics. Question 8. Name, and state formulae for, 3 examples for each of the following: a) acids _______________________________________________________________________________

________________________________________________________________________________ b) bases _________________________________________________________________________________

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c) salts _______________________________________________________________________________ _______________________________________________________________________________

Question 9. Explain why these substances (acids, bases and salts) are classified as: a) compounds rather than elements _____________________________________________________________ b) pure substances rather than mixtures.____________________________________________________________________________________________________________________________________________________________________________

Elements

An element is a pure substance containing only one type of atom. The smallest part of an element is called an atom. The smallest part of an element, which can exist and move independently is called a molecule.

An element is the simplest type of pure substance. It cannot be broken down into anything simpler by a chemical reaction. Ninety-two elements occur naturally and these are the building blocks of matter. Scientists have made about 18 other elements in nuclear reactions, but these are unstable and only last for fractions of a second. Question 10. Use your periodic table to name & state symbols for the first 20 elements. __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ ____________________________________________________________________________________________________________

Occurrence of Elements The elements that make up the Earth have been here since the Earth began. Elements are not changed in chemical reactions, they are only rearranged, and so the elemental composition of the Earth was fixed at its origin. The only changes since then have been the loss of some atmospheric gases into space, the disintegration of some radioactive elements and the arrival of meteors striking the earth's surface. Some of the less reactive elements occur in the crust as the element e.g. gold and silver are both found uncombined with other atoms. However, most elements are reactive, so they are found in combinations on Earth, as compounds, for example:

lead occurs as lead sulfide sodium occurs as sodium chloride and sodium sulfate.

carbon occurs as carbon oxides and in carbonates. Some elements can occur as both the element and as compounds. For example, oxygen is a very reactive element and occurs in the compounds water and in silicate minerals of rocks, however, as it is also a relatively stable molecule, it also occurs as the element in the atmosphere as the element. 8

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Elements are not spread evenly throughout the Earth; their relative predominance varies in the biosphere, lithosphere, hydrosphere and atmosphere. For example, the most abundant element in the universe is hydrogen, which makes up more than 90% of the atoms in the Universe and about 75% of its mass. However, hydrogen makes up less than 1% of the atoms of the Earth. The most abundant elements, by weight, in the Earth’s zones are: Earth’s Zone Elements present Occurs as Biosphere Hydrogen

Oxygen Carbon Nitrogen Calcium

Carbohydrates, proteins, fats & water Carbohydrates, proteins, fats & water Carbohydrates, proteins, fats & water Carbohydrates, proteins, fats Calcium carbonate and calcium phosphate

Lithosphere Oxygen Silicon Aluminium Iron Calcium

These occur as compounds making up the minerals of rocks

Hydrosphere

Oxygen Hydrogen Sodium ions Chloride ions Magnesium ions

Water Water Dissolved minerals in salt and bore water

Atmosphere Nitrogen Oxygen Argon Carbon Hydrogen

Nitrogen gas Oxygen gas & in carbon dioxide Argon gas Carbon dioxide gas Water vapour

Question 11. Explain why hydrogen makes up 90% of the atoms of the Universe and yet only 75% of the mass of the Universe is hydrogen. __________________________________________________________________________________________ _________________________________________________________________________________________ Question 12. Choose 5 metals and 5 non-metals and, for each of these elements, find out how it occurs naturally. ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ ____________________________________________________________________________________________________________________________________________________________________________________ Metals, Non-metals and Semi-metals Elements can be classified, according to their physical properties, as metals, non-metals or semi-metals.

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Property Metals Non-metals Melting point & boiling point High Low Conductivity (heat & electricity) Good Poor (except graphite) Malleability Malleable Non-malleable Lustre Shiny Dull Ductility Ductile Not ductile Semi-metals e.g. boron, silicon, germanium and arsenic, have properties between metals and non-metals. They are all crystalline solids with high melting points, but they have low electrical conductivity. Question 13. We know of oxygen as a colourless gas and yet it is listed as the most common element in the rocks of the lithosphere. Explain. __________________________________________________________________________________________ Question 14. Use the information in the table below to classify each element as a metal or non-metal. Element Melting Point

(0C) Boiling Point (0C)

Conductivity Metal/non-metal

Cobalt 1490 2900 good Bromine -7 58 poor Iron 1540 3000 good Iodine 114 183 poor States of Elements At 250C and normal atmospheric pressure, most elements are solids. Liquid elements are the metal mercury and the non-metal bromine. Gaseous elements are the non-metals nitrogen, oxygen, fluorine, chlorine, and the inert gases, helium, neon, argon, krypton, xenon and radon. Question 15. Name and give the symbol for each of the following: a) a metal which is liquid at room temperature ____________________________________________________ b) a non-metal, which is liquid at room temperature. _______________________________________________ c) 3 elements, which are gases at room temperature ________________________________________________ _________________________________________________________________________________________ Question 16. Use diagrams to explain the difference between an atom of hydrogen and a molecule of hydrogen. Uses of Elements The uses of elements are determined by their physical and chemical properties. Complete the following table to show this. In the last two lines add elements of your choice.

Element Physical Property Chemical Property Use Gold Bright, shiny appearance Unreactive Jewellery Iron Building

Steel Knives and forks

Copper

Good conductor of electricity

Resists corrosion

Neon

Light globes

The Periodic Table of elements The Periodic Table lists all the elements in order of their atomic weight. Vertical Groups show elements with similar chemical properties. For example, elements in Group 1 (Li, Na, K, Rb, Cs, Fr) are all metals (thus have similar physical properties) and they are all chemically active, forming an ion with a +1charge. Horizontal Rows are called Periods. The first period has only two elements, hydrogen and helium. The elements in each period show a range of properties from metallic on the left to non-metallic on the right. Each period represents the filling of an electron shell. 1 11 111 1V V V1 V11 VIII

B C

Si

Ge As Se Sb Te Po

Non-metals

Metals

Semi-metals Question 17. Use your Periodic Table to name the elements in Group 1. Then find out one chemical property and one physical property that they share. Names: __________________________________________________________________________________ Chemical Property:__________________________________________________________________________ Physical Property: _________________________________________________________ ________________ Question 18. Name the elements in Period 4 and state the symbol for each. __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ 11

PARTICLE THEORY and ATOMIC STRUCTURE

Particle Theory

All matter is made of particles, which are continuously in random motion and interacting with each other. This is called the Kinetic Molecular Particle

The particles referred to in this theory can be atoms, molecules or ions depending on the type of substance. The energy of the particles and hence their movement determines the state (solid, liquid or gas) in which the substance will occur. Heating a substance gives it more energy, making its particles move faster and possibly changing its state. Question 19. Explain what is meant by each of the following terms: a) condensation ________________________________________________________ b) sublimation _________________________________________________________ c) density _____________________________________________________________ Solid Liquid Gas

Particles are close together & vibrating in the same place

Particles are close together & moving more freely

Particles are far apart & moving very freely

Definite shape Shape depends on container Shape depends on container Definite volume Definite volume Fills all available space Cannot be compressed Cannot be compressed Can be compressed Question 20. Explain, in terms of particles, what happens to a substance when it changes state from: a) a solid to a liquid ______________________________________________________________________ ______________________________________________________________________________________ b) a liquid to a gas _______________________________________________________________________ _________________________________________________________________________________________ Question 21. State whether heat is absorbed from, or released to, the surroundings when a substance changes from: a) solid to liquid _____________________ ) gas to liquid __________________ b) liquid to gas ______________________ ) liquid to solid __________________

Atomic Structure

Elements are present in the Earth as compounds because of interactions at the atomic level. To understand these interactions, it is necessary to know about the structure of atoms. 12

An atom is the smallest unit of an element with a definite mass, which can take part in a chemical reaction.

Each element has its own unique atoms. Atoms of different elements have different masses as they have different numbers of particles. Every atom is made of 3 main types of particles, called protons, neutrons and electrons, and lots of empty space.

A proton is a small particle, which is positively charged and found in the nucleus of the atom. A neutron is a small particle, which has no charge and is found in the nucleus of the atom. An electron is a very small particle, which is negatively charged and orbits the nucleus of an atom.

In a neutral atom, the number of neutrons equals the number of electrons.

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Electrons are arranged in shells (layers or energy levels) called the K, L, M and N shells. The maximum number of electrons in each shell is 2 in the K shell, 8 in the L shell, 18 in the M shell and 32 in the N shell.

Particle Where found

Symbol Relative charge

Relative mass

Actual charge (coulomb)

Actual mass (kilogram)

proton nucleus p+ H+ +1 1 1.60218x10-19 1.67264x10-27

neutron nucleus n 0 1 0 1.67495x10-27

Electron Orbiting nucleus

e– -1 1/1835 1.60218x10–19 0.91095x10-30

Mass Number of an element is the number of protons plus the number of neutrons in the nucleus of an atom e.g. the mass number of oxygen is 16 This is written as 16O

Electron configuration shows the arrangement of electrons orbiting the nucleus of an atom e.g. the electron configuration of carbon is 2.4, showing that there are 2 electrons in the first (K) shell and 4 in the outer (L) valence shell. Question 22. Show, by means of diagrams, the numbers of protons, neutrons and electrons in an atom of: a) magnesium b) oxygen c) helium d) carbon e) lithium f) sodium g) hydrogen h) chlorine

Question 23. State the symbol, atomic number and mass number for the following: a) iron _______________________________________________________________________ b) aluminium _________________________________________________________________ c) copper ______________________________________________________________________ d) lead ________________________________________________________________________ e) mercury _____________________________________________________________________ Isotopes

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Isotopes are different atoms of the same element with different numbers of neutrons and thus different mass numbers.

Isotopes are atoms of the same element so they have identical electron arrangement and their chemical properties are identical. For example, chlorine exists as chlorine-35 and chlorine-37. Draw diagrams to show these. The relative abundance of the isotopes of an element determines its average atomic mass.

Sample Problem: Chlorine occurs naturally as 75% Cl-35 and 25% Cl-37. Calculate its average atomic mass. Answer: Of every 100 chlorine atoms, 75 have an atomic mass of 35 and 25 have an atomic mass of 37. The average mass of chlorine atoms = 75 x 35 + 25 x 37 100 100 = 35.5 This is called the atomic mass of chlorine.

Because the weight of individual atoms is very small, chemists prefer to compare them to a standard. The standard used is an isotope of carbon, called carbon-12. This atom is taken as having an atomic mass of exactly 12 units, and all other atoms are compared to it. Their masses are then stated as a comparison to this atom,called the relative atomic mass (AR), in atomic mass units (amu). Question 24. Complete the following table: Atomic

number Mass number

No of protons

No of neutrons

No of electrons

Copper-63 29 63 29 34 29 Copper-65 Lead-204

Lead-206

Lead-208 Uranium-235 Uranium-238

Hydrogen-1 Hydrogen-2 (Deuterium)

Hydrogen-3 (Tritium)

Ions

An ion is a charged particle. Ions are formed when atoms gain or lose one or more electrons.

An atom which gains one or more electrons becomes negatively charged and is called an anion, e.g. chloride ion Cl-. Cl + e- Cl→ -

2.8.7 + e- 2.8.8 An atom which gains one or more electrons becomes positively charged and is called a cation, e.g. sodium ion Na+

Na - e- Na→ +

2.8.1 - e- 2.8 Lewis electron dot diagrams can show the formation of ions and ionic compounds. Na + Cl → Na+ Cl Question 25. Explain the difference between an anion and a cation. _____________________________________________________________________________________ ______________________________________________________________________________________ Question 26. Write ionic equations to show the formation of the following ions: a) magnesium ion b) fluoride ion c) sulfide ion d) aluminium ion Question 27. Draw Lewis electron dot diagrams to show the formation of: a) magnesium sulfide b) magnesium chloride 15

Question 22. Use diagrams to show the structure (include protons, neutrons and electrons) of: a) a sodium atom b) a sodium ion b) a chlorine atom d) a chloride ion e) an oxygen atom f) an oxide ion g) a calcium atom h) a calcium ion. Question 29. Explain what is meant by: a) an element __________________________________________________________________________________________ c) an ion __________________________________________________________________________________ The electrostatic attraction between oppositely charged ions is called an ionic bond. Compounds formed by ionic bonds are called ionic compounds. An ionic bond is an electrostatic attraction between positive and negative ions. Ionic bonds usually form between metal ions and non-metal ions. Sometimes the ion contains more than one atom and is called a radical, for example the sulfate ion SO4

2- and the carbonate ion CO32-. Acids, bases and

salts are all ionic substances. Ionic compounds contain ionic bonds. Ionic compounds consist of a lattice of positively and negatively charged ions, held together in a lattice by electrostatic attraction. The formula of ionic compounds is empirical; it shows the ratio of ions in the lattice, not the actual number of ions present. For example, sodium chloride consists of a large array of positive sodium ions and negative chloride ions held tightly together. The formula NaCl indicates that there is one sodium ion present for each chloride ion .

Na+ Cl- Na+ Cl- Na+ Cl-

Cl- Na+ Cl- Na+ Cl- Na+

Na+ Cl- Na+ Cl- Na+ Cl-

Cl- Na+ Cl- Na+ Cl- Na+

Question 30. Explain what is meant by and give two examples of an: a) ionic bond ____________________________________________________________________________ _______________________________________________________________________________________ 16

b) ionic compound _______________________________________________________________________ _______________________________________________________________________________________ Molecules

A molecule is the smallest part of a substance, which is able to exist and move independently. A molecule can contain one or more atoms. Noble gases (Periodic Table, Group V111) exist as single atoms attracted to each other only by very weak forces, called dispersion forces. Gaseous elements such as hydrogen, oxygen and nitrogen cannot exist as single atoms; their molecules contain two atoms (H2, O2, N2) and are called diatomic molecules. These atoms are bound together in the molecule by strong covalent bonds. Molecules of compounds may contain 2 or more atoms joined together by strong covalent bonds. For example, a molecule of water contains 2 atoms of hydrogen and 1 atom of oxygen so is written as H2O. Question 31. Distinguish between an atom and a molecule. _________________________________________________________________________________________ _________________________________________________________________________________________ Question 32. Write symbols/formulae for: a) an atom of oxygen b) a molecule of oxygen c) an atom of argon d) a molecule of argon e) a molecule of ammonia Covalent Bonds Covalent bonds are attractive forces between atoms that occur because

the atoms are sharing one or more pairs of electrons. The shared pair of electrons orbits the nuclei of both atoms, thus holding the atoms together.

Covalent bonds occur within molecules of elements and compounds.

Some elements exist as diatomic molecules, in which the atoms are held together by covalent bonds e.g. Hydrogen H2, Nitrogen N2, and Chlorine Cl2.

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Many compounds exist as molecules in which the non-metal atoms are held together by covalent bonds e.g. Carbon dioxide CO2, Water H2O, Methane CH4, Ammonia NH3. Many polyatomic ions are held together by covalent bonds e.g. Sulfate ion SO42-, Carbonate ion CO3

2-. The covalent bond between atoms can be represented in diagrams as a dash or as 2 circled dots. A molecule of chlorine can be drawn as: Cl—Cl Or Cl Cl Or Cl Cl A double bond occurs when atoms share 2 pairs of electrons, for example: H2C = CH2 Draw this showing the electron dots. Question 33. Use electron dot diagrams to show the arrangement of outer shell electrons of atoms in the following molecules: a) ethane (C2H4) b) methane CH4 c) chlorine gas d) carbon dioxide e) oxygen gas f) water Question 34. Explain the meaning of: a) diatomic ________________________________________________________________________________ b) molecule _______________________________________________________________________________ c) covalent bond ___________________________________________________________________________ d) ionic bond ______________________________________________________________________________ e) electrostatic force ________________________________________________________________________ _______________________________________________________________________________________ f) ionic compound _________________________________________________________________________ Valency

The valency of an element is the combining power of that element.

The valency or combining power of an element with hydrogen is the number of atoms of that element which combines with one atom of hydrogen or which displaces one atom of hydrogen from its compound. The valency

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of hydrogen is always one. For example, in the compound aluminium hydride (AlH3) as the valency of hydrogen is 1, the valency of aluminium must be 3. Note the relationship between valencies of elements and their positions in the periodic table. You should notice that: Metals in Group 1 have a valency of 1. They lose 1 electron in reactions forming an ion with a +1 charge. Non-metals in Group V11 also have a valency of 1. They gain 1 electron in reactions forming an ion with a –1 charge. Metals in Group 11 have a valency of 2.They lose 2 electrons in reactions forming an ion with a +2 charge. Non-metals in Group V1 have a valency of 2. They gain 2 electrons in reactions forming an ion with a –2 charge. Similarly, elements in Groups 111and V will have valencies of 3, and those in Group 4 will have a valency of 4. Question 35. Complete the following table. Group Valency Charge on

ion Ion formed by losing/gaining electron(s)

Number of electrons lost or gained to form ion

I 1 +1 losing 1 electron lost II +3 -1 VII Valencies of Common elements and ions are shown in the table below. Polyatomic ions are charged particles containing more than one type of atom. e.g. sulfate ion SO4

2-

Valency 1 Valency 2 Valency 3 Valency 4 Metals: Sodium Potassium Silver Hydrogen Caesium Copper Lithium

Metals: Barium Iron Chromium Calcium Copper Magnesium Manganese Mercury Nickel Zinc Tin Lead

Metals: Aluminium Iron Chromium Phosphorus

Metals: Tin

Non-metals: Bromine Chlorine Fluorine Iodine

Non-metals: Oxygen Sulfur

Non-metals: Nitrogen

Non-metal: Carbon

Polyatomic ions Acetate ion CH3COO-

Ammonium ion NH4+

Hydroxide ion OH-

Permanganate ion MnO4

-

Nitrate ion NO3-

Polyatomic ins Carbonate ion CO3

2-

Sulfate ion SO42-

Sulfide ion S2-

Polyatomic ions Phosphate ion PO4

3-

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Question 36. Write formulae for the following compounds: 1. potassium chloride _______________ 11. zinc carbonate ______________ 2. calcium sulfide __________________ 12. lithium nitrate ______________ 3. copper (II) oxide _________________ 13. lead sulfide _________________ 4. carbon monoxide _________________ 14. silicon chloride ______________ 5. carbon dioxide ___________________ 15. tin oxide ___________________ 6. copper(I)hydroxide ________________ 16. aluminium phosphate _________ 7. magnesium hydroxide _____________ 17. ammonium carbonate _________ 8. silver oxide _____________________ 18. ammonia ___________________ 9. diphosphorus trioxide _____________ 19. copper (ii) sulfate ____________ 10. barium sulfate __________________ 20. aluminium hydroxide _________ You must also be able to write the names of substances from their formulae. When naming compounds, you should remember that: 1. If the compound is made of a metal and a non-metal, then: • the first name is the name of the metal • the ending of the non-metal is changed to –ide. For example, NaCl is called sodium chloride. • If the metal has more than one possible valency, e.g. ron and copper, the valency is stated in Roman Numerals and placed in brackets e.g. Fe2O3 is called iron(III)oxide. 2. If the compound is made from 2 non-metals, then: • the one from the lower group of the periodic table comes first • the other one ends in –ide • a prefix is used to indicate the number of atoms of each element in the molecule e.g. H2S is called hydrogen disulfide. Question 37. Complete the following table: Name of Compound Formula of Compound Elements that make up the

Compound hydrogen bromide Hydrogen, bromine sodium sulfide Na2S MgCl2 carbon monoxide NO2 dinitrogen trioxide CaC2 FeS Question 38. Write the names of the substances with the following formulae: a) MgO __________________________ d) KBr3 __________________________ b)Ca(OH)2 _______________________ e) KmnO4 _________________________ c) N2O4 _________________________ f) CS2 ____________________________

PHYSICAL and CHEMICAL CHANGES Physical Change Chemical Change No new substances are formed. Particles stay the same.

New substances are formed by rearranging atoms. Atoms are re-arranged to form different particles.

The change is usually easily reversed The change is usually difficult to reverse Small energy changes are involved Energy changes are usually large Examples: change of state (melting, boiling, evaporation, condensation etc), distillation, filtration

Examples: combustion, acids on metals, acids on bases, decomposition by heat or electrolysis

Question 39. What is meant by electrolysis? Include a diagram to show electrolysis of water in your answer. We can look at the differences between physical and chemical changes in water by comparing boiling and electrolysis. Boiling Water Electrolysis of Water Water changes state from a liquid to a gas. The gas is still water.

Water chemically decomposes forming hydrogen and oxygen gases. New substances are formed.

Particles have not changed; each water particle (molecule) still consists of 2 hydrogen atoms joined to 1 oxygen atom.

Particles have changed. Water particles (molecules of H2O) have disappeared. The new particles are molecules of hydrogen (H2) and separate molecules of oxygen (O2).

Reversed by cooling the water vapour. To reverse this process and re-form water, the hydrogen/oxygen mixture must be ignited.

During electrolysis, twice the volume of hydrogen is formed compared to the volume of oxygen, showing that the ratio of hydrogen to oxygen in water is 2:1. This is shown in the formula H2O. Notice that matter is not created in either of these processes. New substances are formed in electrolysis by simply rearranging atoms, not by making new ones.

Chemical Reactions – Decomposition and Synthesis

Decomposition is a chemical reaction in which a compound is broken down into simpler substances.

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This is usually caused by heat or by passing electricity through the compound. Examples: Mercury oxide heat mercury + oxygen 2HgO 2 Hg + O2

Question 40. Write an equation in words and symbols for the decomposition of water by electrolysis. Organic compounds tend to decompose easily when heated, however, inorganic compounds vary. The following table gives some idea of how compounds behave when heated. Note that there are some exceptions that are not covered here. Metal Chloride Carbonate Hydroxide Nitrate Oxide Sulfate Sulfite Potassium Sodium

Stable Stable Forms nitrite & oxygen

Stable

Forms

Barium Calcium

Stable Forms metal

Forms metal

Forms metal

Stable sulfate

Magnesium Aluminium Zinc Iron Tin Copper

oxide and carbon dioxide

oxide and water

oxide, nitrogen dioxide and oxygen

Forms metal oxide and sulfur trioxide

Forms metal oxide and sulfur dioxide

Lead Stable Mercury Sublimes

Do not Forms metal,

Forms

Forms metal,

Forms metal,

Silver Stable exist nitrogen dioxide

metal and

sulfur trioxide

sulfur dioxide

Platinum Gold

And oxygen

oxygen and oxygen

and oxygen

Use the table above to answer the following questions: Question 41. Complete the following rules, based on the information in the table: a) Most hydroxides, carbonates, nitrates and sulfates _____________________________________________ b) Most oxides and chlorides are: ____________________________________________________________ c) Most sodium and potassium compounds are __________________________________________________ Question 42. Name the types of substances formed when the following compounds are heated and decompose. a) Hydroxides____________________________________________________________________________ b) Carbonates ____________________________________________________________________________ c) Nitrates ________________________________________________________________________________ d) Sulfates _______________________________________________________________________________ Question 43. Write balanced equations (use words and symbols) for the decomposition of the following compounds when heated: a) Calcium carbonate b) Mercury oxide

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c) Lead (II) nitrate d) Iron (II) sulfate e) Zinc sulfate

Synthesis is a chemical reaction in which a more complex chemical is formed from simpler substances.

Iron + sulfur iron sulfide Fe + S FeS Sodium + chlorine sodium chloride Na + Cl2 NaCl Energy, in the forms of light, heat or electrolysis, is frequently released or absorbed during decomposition and synthesis. The amount of energy needed to separate atoms in a compound indicates the strength of the bond, the stronger the bond the more energy needed to break it. • Heat and often light are released in all combustion reactions. • Electricity is produced during chemical reactions occurring in batteries. • Electricity is used during electrolysis of substances such as water. •The effect of light on silver salts, such as silver bromide, is the basis of photography. When light falls on silver bromide, silver ions gain electrons forming silver atoms that are deposited on the film. •Photosynthesis uses light energy to make (synthesise) glucose molecules from carbon dioxide and water. Question 44. Write a balanced equation to show the photosynthesis reaction.

Physical and Chemical Properties

Being pure substances, elements and compounds have definite properties, both physical and chemical; however, the properties of mixtures can vary, just as their composition can vary. Physical Properties Physical properties are those that can be found by studying the substance itself, rather than its reactions. Examples of physical properties are: a) Hardness Solids vary in their hardness, generally, the stronger the forces between particles, the harder the substance will be. Hard substances can scratch softer substances e.g. diamond can scratch steel. Some hard substances can be brittle. b) Melting and boiling points

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Type of substance Melting and Boiling Points

Reason

Metals High Strong metallic bonds Covalent molecules (non-metals and compounds)

Low Weak bonds between their molecules

Ionic compounds High Strong bonds between ions c) Conductivity Substances vary in how easily electric charge can flow through them, although they will all conduct electricity if a high enough voltage is applied. Substances, which are good conductors of electricity, are also good conductors of heat. Type of substance Conductivity Reason Metals Good Free electrons Covalent molecules (non-metals and compounds)

Poor No free electrons or ions

Ionic compounds Good in solution Poor when solid

Free ions. Ions are held in a lattice so are not free to move.

d) Malleability Metals are malleable as they can be bent /hammered into shapes. e) Density The density of a substance is its mass per unit volume. Density of a substance depends on the weight of its particles and how closely they are packed together. Density varies greatly, compared to water; hydrogen is only one tenth as dense whereas mercury is 13.6 times greater. Chemical Properties Chemical properties are those that refer to the way a substance reacts. Examples of chemical properties are: a) Chemical activity

Substances vary in their chemical activity. Elements in groups 1 and V11 of the periodic table are very reactive, whereas those in Group V111 are inert.

b) Stability to heat

Some substances, such as sodium chloride are very stable when heated, whereas others, such as mercury oxide, decompose (See table on page 24.) Many substances, such as coke, hydrogen and magnesium undergo combustion when heated. Fuels such as hydrogen, methane and ethanol provide a great deal of energy during combustion. The combustion of glucose in cells is called respiration.

Question 45. Write balanced equations (words and symbols) to show: a) combustion of hydrogen b) combustion of methane (CH4)

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c) combustion of ethanol (C2H5OH) d) respiration.

c) Reaction with acids Substance React with acids to form: Active metals e.g. sodium, magnesium Salt + hydrogen Carbonates e.g. calcium carbonate Salt + water + carbon dioxide Bases e.g. sodium hydroxide Salt + water Question 46. Write equations for the following reactions: a) dilute hydrochloric acid on magnesium b) dilute sulfuric acid on calcium carbonate c) dilute hydrochloric acid on sodium hydroxide Properties of Compounds The properties of a compound are different from the properties of the elements that make up the compound. Some examples from the Earth’s resources are listed in the table below. The first two are filled in for you, complete the others. Compound Properties of

Compound Elements in the Compound

Properties of the Elements

Oxygen

Colourless gas Supports combustion

Water (H2O) Liquid Prevents combustion

Hydrogen Colourless gas Burns explosively

Sodium Active metal Soft, silver solid

Sodium chloride (NaCl)

Neutral salt White crystalline solid Chlorine

Active metal Non-metal Greenish-yellow gas

Alumina (Al2O3) in Bauxite ore

Iron oxide (Fe3O4) in Hematite ore

Carbon dioxide

Copper iron sulfide (CuFeS2) in Chalcopyrite, the main copper ore

Many of the elements mined and separated from compounds in Australia are used extensively. Lead and zinc have already been dealt with; some others are aluminium, copper and iron. Complete the following table: Element Use Aluminium

Copper Electrical conductor in generators, motors, wiring, computers etc. Heat conductor in car radiators, air conditioners, steam condensers, home heating systems. Plumbing, fuel lines, hydraulic systems and sea water desalination plants. (Easy to join with other metals & resists corrosion) Trace element in fertilisers. Forms the sheath around nerve fibres in our bodies, builds proteins that gives blood vessel walls strength and flexibility, activates enzymes & has an anti-inflammatory role in healing.

Iron

Bonding

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A bond is a force holding particles (atoms, ions, or molecules) together.

Metallic Bonding Metallic bonds refer to bonds within a metal when it occurs as the element, not bonds between metals and other elements in compounds.

A metal consists of a three dimensional lattice of positive metal ions in a sea of electrons. The electrons move randomly through the lattice and are shared by the positive ions. This sharing provides the chemical bond, which holds the crystal together.

Metals are good conductors of electricity because these electrons are mobile. Physical Property of Metal Reason High melting and boiling points Strong metallic bonds between the positive

ions and the sea of electrons. A lot of energy is needed to break the bonds.

Good conductivity Electrons are mobile so they can carry current. Malleable and ductile The rows of ions in the lattice can slide over

each other without coming apart or disrupting the bonds.

Shiny (lustrous) The sea of electrons reflects light. Ionic Bonding

An ionic bond consists of a strong electrostatic attraction between positive and negative ions. An ionic compound consists of a repeating three-dimensional lattice of ions. The ionic bonds extend through the whole crystal. Most ionic compounds are crystalline solids at room temperature. They are good conductors when molten or in solution, but do not conduct electricity when solid. This can be explained in terms of their bonds. The formula of ionic compounds is empirical; it shows the ratio of ions in the lattice, not the actual number of ions present. For example, sodium chloride consists of a large array of positive sodium ions and negative chloride ions held tightly together. The formula NaCl indicates that there is one sodium ion present for each chloride ion.

Na+ Cl- Na+ Cl- Na+ Cl-

Cl- Na+ Cl- Na+ Cl- Na+

Na+ Cl- Na+ Cl- Na+ Cl-

Cl- Na+ Cl- Na+ Cl- Na+

Physical Property of Ionic Compounds Reason High melting and boiling points Strong ionic bonds extend throughout the

crystal lattice. A lot of energy is needed to break these strong bonds.

Poor conductors when solid Ions are held in place by strong electrostatic bonds. There are no free ions or electrons to carry the current.

Good conductors when molten Heating makes the ions vibrate faster and move apart, breaking the ionic bonds. Free ions can then conduct electricity.

Good conductors when in solution Water breaks the ionic bonds so ions move apart and are free to conduct electricity.

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Covalent Bonding

Covalent bonds are attractive forces between atoms of non-metals that occur because the atoms are sharing one or more pairs of electrons. The shared pair of electrons orbits the nuclei of both atoms, holding the atoms together.

Covalent bonds occur within molecules of elements e.g.hydrogen and oxygen and compounds e.g. carbon dioxide, hydrogen chloride and ammonia. Many polyatomic ions are also held together by covalent bonds e.g. the sulfate ion. Some covalent substances occur as small covalent molecules e.g. ammonia (NH3), water (H2O), carbon dioxide (CO2), methane (CH4) and ethanol (C2H5O6). In covalent molecular substances, strong covalent bonds hold the atoms together in the molecule, but weak dispersion forces hold the molecules together, so it is easy to pull the molecules apart, resulting in low melting and boiling points. Notice that the molecule itself does not break up when there is a change of state. Physical Property of Covalent Molecular Substance

Reason

Low melting and boiling points Weak dispersion forces are easily broken, molecules move apart and the substance changes state.

Poor conductors when solid, molten and in solution

No ions or free electrons to carry charge.

Other covalent substances occur as giant covalent lattices (also called macromolecules or covalent network) with strong covalent bonds extending throughout the lattice and holding it firmly together e.g. diamond, silica (silicon dioxide SiO2), and polymers. Their boiling points are high.

Physical Property of Covalent Lattice (Network) Substance

Reason

Very high melting and boiling points Strong forces throughout the lattice hold the atoms firmly together.

Poor conductors when solid, molten and in solution

No ions or free electrons to carry charge.

Question 47. For each of the following compounds, state its formula and the type of bonding present in the compound. Name Formula Bonding Carbon dioxide Sodium oxide Iron (III) chloride Calcium sulfate

Polar Covalent Bonds When the atoms sharing electrons are identical (e.g. H2, Cl2, N2) electrons are shared evenly between the atoms.

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When the atoms sharing electrons are different (e.g. HCl, H2O, NH3) electron pairs are unevenly shared; electrons spend more time near one nucleus than the other. For example, in hydrochloric acid, the shared pair of electrons spend more time near the chlorine atom than the hydrogen atom. Thus the chlorine end of the molecule is slightly positive and the hydrogen end is slightly negative. When electrons are shared unevenly like this, the bond is called a polar covalent bond.

A polar covalent bond is one in which electrons are shared unevenly so there is a net dipole. The atom that attracts the electron(s) more firmly is said to be more electronegative; it has greater electron-attracting ability. Question 48. From the following list, circle any substance which has polar covalent bonds: methane, hydrogen gas, hydrogen fluoride gas, water, carbon dioxide, ammonia. A particle with oppositely charged ends is called a dipole. If a covalent substance has more than 1 polar bond the dipoles may cancel each other out so that the molecule itself is not polar e.g methane (CH4). If molecules are shaped so that dipoles do not cancel out, the whole molecule becomes polar e.g. water contains 2 polar O-H bonds. A molecule water is a bent shape because of the arrangement of its electrons, so there is a net dipole, the 2 dipoles do not cancel each other out, and water molecules are polar.

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Revision Exercises

Multiple Choice 1. A mixture of liquids could best be separated by the technique of: A. filtration

B. fractional distillation C. chromatography D. crystallisation 2. In the periodic table below, the metal with a valency of 2 would be found in position: S P R Q

A. A B. Q C. R D. S

3. When water boils A. bubbles of hydrogen and oxygen are formed B. water molecules split into atoms C. water molecules move faster and further apart D. covalent bonds in water are broken 4. The most abundant element, by weight, in the Earth’s crust is: A. oxygen B. hydrogen C. iron D. silicon 5. An anion is: A. a positive ion formed by gaining electrons B. a negative ion formed by gaining electrons C. a positive ion formed by losing electrons D. a negative ion formed by losing electrons

Short Answer 1. Answer this question in table form. a) Name 4 metals and give the symbol for each. b) Using the Chemical Data book: (i) Find 3 physical properties that these 4 metals have in common (ii) Find properties that would allow you to distinguish between these metals.

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2. Repeat question 1 using 4 non-metals. 3. Explain how the Particle Theory of matter can be used to explain: a) A gas can be compressed whereas a solid and a liquid cannot. b) Melting of a solid when heated. c) Solids have a definite shape but gases and liquids do not. 4. Use the information in the table below to classify the substances listed as solid, liquid or gas at a temperature of 25oC. Substance Melting Point (0C) Boiling Point (0C) State (at 250C) Sodium 98 892 Sodium chloride 800 1465 Ethane -183 -88 Water 0 100 Graphite (carbon) 3730 4830 5. Sketch a graph to show water being heated from –100C to 1100C. 6. Classify each of the following substances as an element, compound or mixture: a) petrol b) steel c) blood d) coca-cola e) crude oil f) iron g) aluminum h) water i) liquid nitrogen j) air 7. Classify each of the following as a physical or a chemical change:

a) burning of wood b) souring of milk c) electrolysis of water d) condensing steam e) melting iron f) bending iron g) rusting of iron h) water freezing

8. Complete the following table to show differences between metals and non-metals. Physical Property Metals Non-metals Appearance Conductivity Melting & boiling points 9. The valency of hydrogen is 1 and the valency of oxygen is 2. The formulae of some compounds are, NaH, CaO, CO2, P4O10, and AlH3. Using this information, find the valencies of: a) sodium b) calcium c) carbon d) phosphorus e) aluminium. 10. Write formulae for the following compounds: a) hydrochloric acid f) silver oxide b) iron (III) chloride g) aluminium sulfate c) potassium fluoride h) calcium carbonate d) sodium hydroxide i) zinc hydroxide e) potassium phosphate j) sulfuric acid

11. Use information on the Periodic Table to complete the following. Element Symbol Atomic

number Number of protons in an atom

Number of electrons in an atom

Mass number

Number of neutrons in an atom

Sulfur Magnesium Chlorine 12. Balance the following equations: a) HCl + NaOH NaCl + H2O b) Mg + O2 MgO c) HgO Hg + O2 d) Al + H2SO4 Al2(SO4)3 + H2

13. Write word equations and balanced symbolic equations for each of the following reactions: a) A solution of barium chloride is added to a solution of sodium sulfate. The products formed are a colourless solution of sodium chloride and a white precipitate of barium sulfate. b) Dilute sulfuric acid reacts with zinc carbonate to form a solution of zinc sulfate, water and bubbles of the gas carbon dioxide. c) Dilute hydrochloric acid reacts with magnesium forming a solution of magnesium chloride and bubbles of a gas, which ‘pops’ when ignited. 14. the industrial separation technique you researched and for this technique describe: a) the mixture being separated b) the property used in this technique to separate the components of the mixture c) the impact of the development of this technique on chemistry. 15. Complete the following table to show a mixture present in each of the Earth’s zones that can be used without separation procedures. Zone Mixture present Use Biosphere Lithosphere Atmosphere Hydrosphere 16. a) What is gravimetric analysis. b) Describe an experiment you performed in the laboratory that utilized this technique. 17. Explain how the technique of electrolysis helps us understand the composition of compounds such as water.

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18. Describe an experiment you performed in the laboratory that allowed you to compare the properties of a compound with those of the elements that constitute that compound. 19. Write electron dot formulae for: a) a lithium atom b) a lithium ion c) an oxygen atom d) an oxygen ion e) oxygen gas f) a molecule of ammonia. 20. Explain, in terms of bonding why: a) potassium chloride conducts electricity when molten, but not when solid b) copper is a good conductor of electricity c) iodine is a poor conductor of electricity. 21. Copper contains 69.1% copper-63 and 30.9% copper-65. Calculate the relative atomic mass of copper.