Chapter 2

Introduction to Chemistry

Composition of Matter• Matter is anything that occupies

space and has mass.• Mass is the quantity of matter an

object has.• Mass and weight are different.• Weight depends on the amount of

gravity.• You would weigh less on the moon

than on earth but have the same mass.

• http://www.exploratorium.edu/ronh/weight/

What is matter?air water

smoke

light

heat

cold

darkness

jello sound

human

Element

• An element is a pure substance that cannot be broken down into simpler kinds of matter.

• Each element has a different chemical symbol.

• More than 100 elements have been identified.

• More than 90% of the mass of living things is composed of oxygen, carbon, hydrogen and nitrogen

Atom• An atom is the simplest part of an element that

retains the properties of that element.• The properties of atoms determine how the

element will behave in nature.• An atoms consists of three parts.• The nucleus contains protons and neutrons.• Electrons float around the outside of the

nucleus.• The number of protons is called the atomic

number.• Protons are charges positively, electrons are

negative and neutrons are neutral or zero charge.

Atomic ParticlesName of Particle

Location Charge Related Info

Proton Nucleus + Measured by atomic number

Neutron Nucleus 0 Measured by atomic mass

Electron Outside the nucleus

- Helps with bonding

Electrons

• Electrons are responsible for making chemicals.

• Electrons are set in different layers called energy levels.

• Each level can hold up to 8 electrons except the innermost level which can only hold 2.

Compounds• A compound is a pure substance made up of

two or more elements.• A chemical formula shows what elements and

how many are in a compound.• An atom is chemically stable when its outer shell

has 8 electrons with the exception of helium and hydrogen.

• That is why elements bond together.• When elements bond together they create a

chemical reaction which makes the atoms happy and stable.

Covalent bonds

• Covalent bonds form when atoms share one or more pairs of electrons.

• This usually happens between nonmetals.

• A molecule is formed when a covalent bond is used.

• Examples are: water, carbon dioxide and oxygen gas

Ionic Bonds

• Ionic bonds form when one atom transfers electrons from itself to another atom.

• When this occurs, an ion is formed.

• Ionic bonds usually happen between a metal and a nonmetal.

Energy and Matter

• Energy is the ability to do work or cause change

• Free energy is the energy in a system available for work.

• There are three main states of matter.

• Solid, liquid and gas.

Energy and Chemical Reactions• Living things undergo thousands of

chemical reactions as part of their life processes.

• The reactants are shown on the left side of the equation.

• The products are shown on the right side.

• Reactants are converted to products.• Energy is required for the chemical

reaction to occur.

A chemical reaction must make something totally different that has different properties from when it started.

You start with the reactants And you end with the products

When you make a sandwich, what do you do?

When you make a sandwich, what do you do?

Reactants

Products

How can you recognize a chemical reaction?

Breaking glass

Frying an egg

Shaking pop

Ice pack

Burning a match

Freezing water

Hand warmers

Cooking macaroni

Rusting car

Boiling water

Chopping veggies

Baking a cake

Energy Transfer

• Chemical reactions that release energy are called exergonic reactions.

• Chemical reactions that absorb energy are called endergonic reactions.

• Both exergonic and endergonic reactions require energy to start the process.

• This is called activation energy.• Certain chemicals called catalysts, reduce

the amount of activation energy required.• The reaction happens easier.• One catalyst in the body is called an

enzyme.

Redox reactions

• Many chemicals reactions that help transfer energy in living things involve the transfer of electrons.

• These are called reduction-oxidation reactions or redox reactions.

• In oxidation, a reactant loses one or more electrons, making it a positive ion.

• In reduction, a reactant gains one or more electrons making it more negative.

• There is always an atom that is oxidized and an atom that is reduced.

Solutions• A solution is a mixture in which one or more

substances is uniformly distributed in another substance.

• A solution has two parts.• The solute is the substance dissolved in the

solution.• The solvent is the substance in which the solute

in dissolved.• The concentration is the measurement of the

amount of solute dissolved in the solvent.• A saturated solution is one in which no more

solute can dissolve.• An aqueous solution are solutions in which water

is the solvent. These are very common.

Acids and Bases• Dissociation is the breaking apart of water.• When water breaks, two things are made.• The hydroxide ion is OH-• The hydrodium ion is H3O+• If the number of hydrodium ions is greater

than the number of hydroxide ions, the solution is an acid.

• Sometimes hydrodium is just written H+• If the number of hydroxide ions is greater than

the hydrodium ions, then the solution is a base.

pH and Buffers• pH is the scale for comparing the relative

concentrations of hydronium in a solution.• The scale ranges from 0 to 14.• The smaller the number, the more acidic a

solution is. The higher the number, the more basic it is.

• For example, stomach acid has a pH of about 2. Ammonia has a pH of about 12.

• Buffers are chemicals that neutralize acids and bases in the body.

• Buffers help maintain good pH levels in the body.

Exchange or give/take

Which have an electric

Which makes

Atoms electronsCharge

Ionic bonds and Ions

share

Which makes

Moleculeselectrons

Covalent bonds

Essential Questions• How are particles arranged in an atom?• How does an ionic bond differ from a covalent

bond?• Why doesn’t Neon combine with elements very

often?• What are the 3 state of matter?• Explain how a catalyst affects a reaction.• Why does a reduction always happen with an

oxidation?• Describe the dissociation of water.• What is neutral pH?• What is a buffer? Why is it important to the

body?