Chemistry Notes Term 1 – The Chemical Earth

Construct word and balanced formulae as they are encountered

Types of Chemical Reactions

Synthesis:

One new chemical being formed

e.g. 2Mg(s)+O2(s) -> 2MgO(s)

A + B -> A:B

Decomposition:

One chemical broken down into 2 or more

e.g.MgCO3(s) -> MgO(s)+CO2(g)

A:B -> A + B

Displacement Reaction:

One chemical takes the place of another

e.g.CuSO4(aq) + Mg(g) -> MgSO4(aq) + CU(s)

A:B + C -> A:C + B

Double Displacement Reaction

Two chemicals takes the place of two others

e.g. Pb(NO3)2 + 2NaCl(aq) -> PbCl2 +2NaNo3(aq)

A:B + C:D -> A:C + B:D

Common Reactions

Combustion:

a) Element + Oxygen Element Oxide

b) Hydrocarbon + Oxygen Carbon dioxide + Water

Metal + Acid = Metal Salt + Hydrogen

Metal + Water = Metal Hydroxide + Hydrogen

Metal + Oxygen = Metal Oxide

Identify the difference between elements, compounds and mixtures in terms of particle theory.

All matter is made of continually moving matter

Elements:

Simplest pure substances consisting of only one types of atom. They cannot be decomposed. They are homogenous.

Compounds:

Pure substances composed of two or more elements that are chemically bonded together. Have fixed amounts of atoms of each component bonded together and can be decomposed into elements or simpler compounds. Homogenous.

Mixtures:

2 or more elements or compounds that aren’t chemically bonded and are easily separated by physical processes. Can be heterogeneous or homogenous.

Properties: There will be a combination of properties of the constituent chemicals. E.G. An Iron-Sulphur mixture would be a dirty yellow colour having blended the yellow of the sulphur with the grey of the iron.

Identify biosphere, lithosphere, hydrosphere and atmosphere contain examples of mixtures of elements and compounds

The Earth and it’s spheres:

Biosphere:

Where living things are found.

Most living things are composed of cells. Cells contain large amounts of water, hence, oxygen and hydrogen are abundant in the biosphere.

Lithosphere:

Crust and top part of mantle

Contains many different types of minerals that are combined in different proportions to form sedimentary, igneous and metamorphic rocks.

Hydrosphere:

Discontinuous layer on Earth

Contains all soluble substances

Water is abundant compound in the hydrosphere.

Atmosphere:

Gaseous layer around the Earth

Identify and describe procedures that can be used to spate naturally occurring mixtures of: Solids of different sizes, Solids and Liquids, Dissolved solids in liquids, Liquids, Gases.

Solids of different sizes

Sieving

Used in:

Cooking, bar screens and sewage filtration

Solids and Liquids

Sedimentation and Decantation

Solids of different mass either float or sink. By tipping the liquid and floating substances, the sunken substances are left

Uses:

Water Treatment

Filtration

The less dense through

Uses:

Sewage

Swimming pool

Froth floatation

Uses:

Treatment of metal ore

Dissolved solids and liquids

Fractional Distillation

The apparatus contains a fractionating column which consists of hundreds of glass beads. This arrangement allows for repeated condensations and evaporations, thus the solution is distilled 10-100 times. Liquid with the lowest b.p comes off first

Uses:

Fractional Distillation of crude oil

Evaporation

Different boiling points of liquids

Uses:

Production of Salt

Liquids

Centrifugation

Liquids of different density

Uses

Separation of colloids of milk, hence skim milk

Separation of blood

Chromatography

A medium (paper), then run the solvent up the medium which separates mixture based solubility. The higher up it runs, the more soluble it is.

Uses:

DNA profiling

Separating Funnel

2 immiscible liquids

Uses

Separating oil from water

Extract perfume from mixture

Gases

Fractional Distillation. Gases are condensed to liquid state then distil

Differences in solubility. Gases are run through a series of “u” shaped tubes each containing a substance that will dissolve a particular gas, thus leaving only the desired gases at the end.

Solids (Magnetic)

Magnetic Separation

Uses

Rubbish recycler

Assess separation techniques for their suitability in separating examples of earth materials, identifying the differences in properties which enable these separations

Describe situations in which gravimetric analysis supplies useful data for chemists and

Analysis of the composition of a substance by its mass or weight may be undertaken to determine:

The percentage of a required mineral

Soil composition e.g. Sulfate content

Extent of toxicity of a body of water

Quality control

Pollution control

% w/w = Percentage weight for weight

E.g. Students analysed a 6.13g sample of fertiliser and determined that it contained 2.13g of magnesium sulphate. What is the % w/w composition of MgSO4 in the sample?

2.13/6.13 = 33.8 % w/w

%w/v = Percentage weight for volume

E.g. Water is 1g/cm3

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Explain the relationship between the reactivity of an element and the likelihood of its existing as an uncombined element

Unreactive

Can exist freely because they do not require losing or gaining electrons, hence they do not react. This means they are able to exist by themselves.

Cannot exist freely because they are too reactive to be stable, hence by forming a stable shell, by combining with other elements or themselves, they can stabilise, hence exist as a compound.

Classify elements as metals, non-metals and semi-metals according to their physical properties

Refer to notes

Identify that matter is made of particles that are continuously moving and interacting

In particle theory, all matter is made up of constantly moving particles

Metals

Particles are in order

Vibrate

Liquids

Particles are in less order

Translational and vibrational

Gas

Particles are well away from each other

Rapid translational movement

Describe qualitatively the energy levels of electrons in atoms

Valence electrons found in most outermost shell, therefore have highest energy

The number of electrons indicates how reactive the element is

Describe atoms in terms of mass number and atomic number

Mass number = Neutrons + Protons

Atomic number = Proton number = Electron number

Describe the formation of ions in terms of atoms gaining or losing electrons

Metals form cations (positive) when they are ions. This is because they are on the left side of the periodic table, hence their valencies are 1+,2+ and 3+. It is much easier to lose electron than to gain.

Non-metals form anions(negative) when they are ions. This is because they are on the right side of the periodic table, hence their valencies are 3-,2-,1-. For them , it would much easier to gain electrons than to loose them.

If the element has a valency of 4, it either lose or gain.

Hydrogen can also lose or gain an electron as it only has one electron, hence it is easy for it both ways.

See above

Describe the formation of ionic compounds in terms of the attraction of ions of opposite charge

Ionic bonding is when Metals and Non-metals bond through electrostatic means attraction. The Cation (Metal) gives the Anion(Non-metal) it’s valence electrons, hence forming a bond.

This bond is strong due to it’s lattice structure.

Describe molecules as particles which can move independently of each other

Molecules are made up of several atoms joined together by intramolecular forces.

Molecules are particles that may move independently of each other. The forces that hold the molecules together are known as intermolecular forces. If these forces break (caused by energy such as hammer to shatter or boiling) the molecules break free from the intermolecular forces and roam free.

Intramolecular forces are broken down to start chemical reactions. Methods such as electrolysis can break intramolecular bonds, which allow atoms/ions to roam freely to make stable bonds. This energy is known as activation energy

Distinguish between molecules containing one atom (the noble gases) and molecules with more than one atom

Mono-atomic molecules (Noble gases)

Di-atomic molecules( H2,O2,N2 etc)

Only non-metals

Describe the formation of covalent molecules in terms of sharing of electrons

Covalent bonds form when non-metals share their electrons to reach a stable status.

There are 3 types of covalent bonds

Single, Double and Triple bonds

Covalent bonds can be polar, meaning the more electronegative element will attract electrons more strongly

There are 2 types of structures

Covalent Network

Where molecules are held together by INTRAmolecular bonds

Lattice structure

Covalent Molecular

Where molecules are held together by INTERmolercular bonds

See workbook

Identify the differences between physical and chemical change in terms of rearrangement of particles

Chemical Change is when the intramolecular forces are broken, hence a new substance is produced

Chemical Change Indicators

Colour change

Precipitate forms -> New insoluble product

Gas forms (bubbles)

Energy Change

Light

Heat

Sound

Electricity

Physical Change is when the intermolecular forces are broken, hence no new substances are formed, rather the substance just changes state. E.g. Ice into Water.

Difference between the boiling and electrolysis of water as an example of the difference between physical and chemical change

Identify light, heat and electricity as the common forms of energy that may be released or absorbed during the decomposition or synthesis of substances and identify examples of these changes occurring in everyday life

EXOTHERMIC -> gives off heat

Additional energy released as new bonds form e.g. light, sound and heat

ENDOTHERMIC -> takes in heat

More energy taken in then given out therefore mixture usually cools down

Decomposition is the breaking of a compound

Synthesis is the formation of new compounds which is mostly initiated by heat but also by light and electrical energies.

Explain the amount of energy needed to separate atoms in a compound is an indication of the strength of the attraction or bond between them

The amount of energy needed to decompose chemical compounds and mixtures is indicative of the strength of the bonds. The easier the intermolecular bond is to break, the more reactive the element is. For example, Sulphate requires less energy to break its bonds as it is more reactive say, Magnesium Oxide.

Similarly in intramolecular bonds, the reason why some compounds can be broken by boiling while others can be broken by electrolysis indicates how strong the attraction is.

Identify differences between physical and chemical properties of elements, compounds and mixtures

Describe the physical properties used to classify compounds as ionic or covalent molecular or covalent network

Ionic

Covalent Network

Covalent Molecular

Solid

Solid

Solids, Liquid

High mpt bpt

High mpt bpt

Does not conduct electricity or thermal

Does not conduct electricity or thermal

Do not conduct electricity or thermal

Good conductor when molten

Brittle because distortion breaks covalent bonds

Does not conduct electricity unless reacted with water to form ions

Lattice Structure

Lattices held by intramolecular forces

Held by weaker intermolecular forces

Distinguish between metallic, ionic and covalent bonds

Metallic bonding forms between metals. The structure is cations surrounded by a sea of delocalised anions

Highly conductive electricity and thermal

Malleable

Solids besides Mercury

Ductile

The higher the group, the more electrons per atom, hence stronger bonds

Ionic bonding is between a metal and non metal – where the metal gives electrons while non metals take electrons

May carry electrons in aqueous state

Covalent bonding is between non metals – where the non-metals share their electrons

2 types

Molecular

Network

Describe metals as 3D lattice of ions in a sea of electrons

Metallic bonding is cations in a sea of anions made up of 3D lattice

Describe ionic compounds in terms of repeating 3D lattices of ions

Ionic compounds form 3D crystal lattices, causing them to be very strong and not able to conduct electricity/thermal. The cations and anions bond infinitely, hence it repeats

Explain why the formula for an ionic compound is empirical

Because ionic compounds can form infinitely, it would be impractical to record the exact amount of anions and cations, instead, we find the ratio – which is the empirical formula was use.

Identify common elements that exist as molecules or as covalent lattices

Covalent Molecules

All diatomic gases

Nitrogen, Oxygen, Iodine, Fluorine

Phosphorous exists as P4

Sulfur exists as S8

Covalent Lattices

Carbon exists as diamond 3D lattice and graphite 2D lattice

Explain the relationship between the properties of conductivity and hardness and the structure of ionic, covalent and network structures

Ionic

Hard (Lattice)

Non conductive (No free electrons however there are in aqueous)

Covalent Network

Hard

Non conductive

Covalent Molecular

Weaker bonds