Introduction to

Chemistry

I. Chemistry is a Physical Science

Objectives:• Define chemistry.• List examples of the branches of

chemistry.• Compare and contrast basic

research, applied research, and technological development

What is Chemistry?

1) Chemistry = the study of the composition, structure, and properties of matter and the changes it undergoes.

6 Branches of Chemistry1. Organic chemistry = study of carbon-containing

compounds2. Inorganic chemistry = study of all substances not

classified as organic, mainly those compounds that do not contain C

3. Physical chemistry = study of the properties and changes of matter and their relation to energy

4. Analytical chemistry = identification of the components and composition of materials

5. Biochemistry = study of substances and processes occurring in living things

6. Theoretical chemistry = use of mathematics and computers to understand the principles behind observed chemical behavior and to design and predict the properties of new compounds.

Science vs. Technology

• Science includes knowledge in the major disciplines, such as biology, chemistry, and physics.

• Technology is the application of that knowledge for practical purposes.

• Basic research = research conducted for the sake of knowledge only and not to meet practical goals

• Applied research = research conducted to meet goals defined by specific needs

• Technology = applies existing knowledge to make life easier or more convenient

II. Matter and Its Properties

Objectives:• Distinguish between the physical

properties and chemical properties of matter.

• Classify changes of matter as physical and chemical.

• Explain the gas, liquid, and solid states in terms of particles.

• Distinguish between a mixture and a pure substance.

Energy vs. Matter

• EVERYTHING that you see or sense is either matter or the interaction of energy and matter!

1) Energy = the ability to cause change or the ability to do work.

2) Matter = anything that has mass and takes up space.

Classification of Matter

1) Pure substance = a type of matter that has a consistent, fixed composition no matter where the sample is obtained.

a) Ex: water (a pure substance) is ALWAYS 11.2% hydrogen and 88.8% oxygen (by mass).• So a molecule of water from India has

the same compositions as a molecule of water from Canada.

b) PURE SUBSTANCES are either elements or compounds

Classification of Matter

2) Element = pure substance made of only one kind of atom.

a) atom = smallest unit of an element that maintains the properties of that element.

Classification of Matter

3) Compound = a pure substance that is made from the atoms of two or more elements that are chemically combined.

a) Individual elements lose their individual properties and take on

the new properties of the compound that is formed.

b) Ex: sodium (an element) is a highly reactive metal and chlorine (an

element) is a poisonous gas; chemically combined they form sodium chloride (a compound) which is common table salt.

Classification of Matter

4) Mixture = a blend of two or more pure substances that are physically combined where each pure substance retains its own identity and properties• Ex: silver coins + gold coins =

mixture; the silver coins are still silver coins and the gold coins are still gold coins.

V. Classification of Matter

• Characteristics of mixtures:1. Represent physical combinations of

two more substances2. Substances do not lose their original

properties.3. Substances can be separated by

physical means.• Two types of mixtures are

homogeneous and heterogeneous.

5) Homogeneous mixture (solution) = a mixture that is uniform in composition throughout an entire sample.• Ex: if you were to take one scoop out

of one area of a homogeneous mixture and a second scoop out of a different area of the same sample, the composition of each scoop would be essentially the same.

• Ex: salt water, air, window glass.

Homogeneous mixture cont.

• Also called solutions – consist of a solute (dissolved material) in a solvent (dissolving material)

• Important symbol in chemistry is the subscript “aq”, which stands

for aqueous.• An aqueous substance is one that is

dissolved in water … AKA a solution!

• NaCl(s) – This formula represents a solid substance, the compound NaCl in a solid form.

• NaCl(aq) – This formula represents a homogeneous mixture of NaCl and water.

6) Heterogeneous mixture = a mixture that is NOT uniform in composition throughout an entire sample. • Ex: chicken soup, sands, soil.

How would you classify the following matter?

ASPIRIN (C9H8O4) is composed of 60% carbon, 4.5% hydrogen, and 35.5% oxygen by mass, regardless of its source.

Is aspirin a mixture or a pure substance?

Element or compound?

Pure substance – constant composition

Compound

How would you classify the following matter?

SALT WATER

Is salt water a mixture or a pure substance?

What type of mixture?

Mixture – can be separated by evaporation

Homogeneous mixture

Properties of Matter

• What is a property?

• 2 methods of grouping properties

1. Extensive and intensive

2. Physical and chemical

• Extensive = property that depends on the amount of matter (mass, volume)

• Intensive = property that does not depend on the amount of matter present (color, melting pt., boiling pt.)

Properties of Matter

1) Physical property = a characteristic that can be observed or measured without changing the identity of a material.

• Physical properties describe matter.• Ex: state, color, odor, solubility,

density, melting point, boiling point, hardness, mass, texture

Properties of Matter

2) Chemical property = the ability of a substance to undergo a change that alters its identity.• Chemical properties describe the

ability of matter to change identity.• Ex: flammability, reactivity with acid,

resistance to rusting, ability to decompose.

Changes

1) Physical change = any change in a property of matter that does NOT result in a change in identity.

• Ex: water freezing, water vapor condensing, wood being chopped, glass being broken, an iron rod being bent

Changes

2) Chemical change (chemical reaction) = a change in which one or more substances are converted into different substances with different characteristic properties.• Ex: paper burning, silver tarnishing,

wood decomposing, iron rusting.

Chemical vs. Physical change:

Chemical change (chemical reaction)

1) Indications of a chemical change (reaction):

a) Evolution of heat and lightb) production of a gas (seen as

bubbles)c) color changed) formation of a precipitate when two solutions are mixed. precipitate = a solid that separates from a

solution.

Formation of a PRECIPITATE

Precipitate of cadmium sulfide forms from clear

solutions of sodium sulfide and cadmium

nitrate.

Chemical change (chemical reaction)

2) In order for a chemical reaction to take place, the reactants must have the ability to form chemical bonds.• Parts of a chemical reaction:– REACTANTS = substances that interact

with each other. On the left side of the arrow in a chemical equation.

– PRODUCTS = new substances formed during reaction. On the right side of the arrow in a chemical equation.

– EX: hydrogen + oxygen water + heat

Chemical change (chemical reaction)

3) Law of Conservation of Matter = matter is neither created nor destroyed during ordinary chemical and physical changes.• As a result of the law of conservation of matter,

the mass of the reactants in a chemical reaction must EQUAL the mass of the products.

• If you START off with 10g of matter before a physical or chemical reaction, you will END up with 10g of matter.– These changes don’t create or destroy atoms, they

only change how the atoms are bonded to each other!

Energy Changes

1) Energy = the ability to cause change or the ability to do work

• Heat = form of energy– Heat FLOWS from

objects with a high temperature to objects with a lower temperature.

Energy Changes

NOTE: A chemical change is ALWAYS accompanied by a change in

ENGERGY!!2) Chemistry deals with the chemical energy stored in matter and with either the effects on matter or the production of energy from matter.

Energy Changes

3) Activation energy is the energy needed to start a chemical reaction.• All chemical reactions require energy

to begin!– Enough energy is available from the

environment to start some reactions.– For others, additional energy must be

added before the reaction will begin.

Energy Changes4) Endothermic process = a process that absorbs heat• The products have MORE

energy than the reactants.• Energy must be absorbed

as the products form.• The container in which an

endothermic reaction is taking place will feel cold.

• Ex: chemical cold packs, ice melting.

Energy Changes5) Exothermic process = a process that releases heat.• The reactants have MORE

energy than the products.• Energy must be released

as the products form.• The container in which an

exothermic reaction is taking place will feel hot.

• Ex: chemical hot packs, lighting a match.

Exothermic process

Ex: CH4 (g) + 2O2 (g) CO2 (g) + 2H2O (g) + ENGERY

REACTANTS PRODUCTS

4 States of Matter

1. Solid = definite volume and definite shape

2. Liquid = definite volume but no definite shape

3. Gas = neither definite volume nor definite shape

4. Plasma = high-temperature physical state of matter in which atoms lose their electrons

III. Elements

Objectives:• Use a periodic table to name

elements, given their symbols.• Use a periodic table to write the

symbols of elements, given their names.

• Describe the arrangement of the periodic table.

• List the characteristics that distinguish metals, nonmetals, and metalloids.

• For a chemist, the periodic table is the most useful source of information about the elements.

• Groups = families = vertical columns (these elements have similar properties)

• Periods = horizontal rows• Symbols are sometimes derived from

Latin.

Write the symbol, group, and period for each of the following:

1. Potassium2. Oxygen3. Aluminum4. Cesium5. Sodium

6. Sulfur7. Zinc8. Cobalt9. Neon10.Iodine

Types of Elements

• 3 Types:– Metals: good conductor of heat and

electricity • other properties include: malleability, tensile

strength, ductile, solid at room temp. silvery or grayish luster, reactivity

• Majority of periodic table

– Nonmetals: poor conductor of heat and electricity • Other properties include: many are gases; solids

are brittle • Top right corner of periodic table

Types of Elements

–Metalloids: properties of metals and nonmetals• Other properties include: semiconductors of

electricity, used in computers and calculators• 6 elements form stair steps (B, Si, Ge, As,

Sb, and Te)

Noble Gases

• Noble gases = group 18• Unreactive• Gases at room temp.

Complete p. 23 #1,2,4-15, 20-21

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