The Particle Theory
Chapter 2

The Particle Theory
More than 2000 years ago, a Greek
philosopher Democritus suggested that
matter was made of tiny particles too
small to be seen.
He thought if you kept cutting a substance
into smaller and smaller pieces, you would
find the building blocks of matter.

4 Principles of the Particle Theory
1. All matter is made of tiny particles.
2. All particles of one substance are the same.
- Different substances are made of
different particles.
3. The particles are always moving.
- The more energy the particles have, the
faster they move.
4. There are attractive forces between
particles.
- These forces are stronger when the
particles are closer together.

 Theparticle theory helps to explain two
categories of substances that are
encountered in chemistry.

Two Categories of Substances
Category 1: Pure Substances
- contains only one kind of particle
- Types: elements and compounds
Category 2: Mixtures
- contains two or more different pure substances
- Types: homogeneous and heterogeneous mixtures

Category 1: Pure Substances
Type 1: Elements
– pure substances that cannot be broken down
into simpler substances
- Examples: think Periodic table (oxygen,
hydrogen)
Type 2: Compounds
– pure substances that contain two or more
elements
- Examples: Water (H2O), sugar (C6H12O6)

Category 2: Mixtures
Type 1: Homogeneous (also known as solutions)
– may be made up of solids, liquids or gases
- this mixture is uniform (the same) throughout
- Examples: air, alloys, kool aid, white vinegar,
orange juice without the pulp
Type 2: Heterogeneous
– see each part easily, separated physically
- this mixture is not uniform throughout
- Examples: pizza, garbage, beach sand,
vegetable soup

How to Classify Mixtures
 When two pure substances are mixed
together, they may mix smoothly or unevenly.
 If the substances mix well with one another,
the mixture is called a solution.
 If the particles don’t mix well together then we
have a heterogeneous mixture.

Classify the Following
 Salt and water
 solution
 Pizza
 heterogeneous mixture
 Garbage
 heterogeneous mixture
 Air
 solution

Atoms and Molecules
 Atoms
- each atom is made of one type of element
- scientists now call the particles in the particle theory atoms
- the periodic table of elements has 118 elements
 Molecules
- contains two or more atoms joined together in combinations
- Ex. C4H8 – contains 4 carbon atoms and 8 hydrogen atoms

Guess the Molecule
I have 2 hydrogen atoms
 I have 1 oxygen atom
 I am water

Guess the Molecule
 I have 10 hydrogen atoms
 I have 2 oxygen atoms
 I have 7 carbon atoms
 I have 4 nitrogen atoms
 I am desired in the morning but
avoid me in the evening
 Cola drinks have contain me
 I am what makes coffee
special
 I am caffeine

Guess the Molecule
 I have 6 hydrogen atoms
 I have 6 oxygen atoms
 I have 6 carbon atoms
 Everybody needs me
 I will help keep colds away
 You can get me by eating
oranges
 I am vitamin C

Guess the Molecule
 I have 8 hydrogen atoms
 I have 4 oxygen atoms
 I have 9 carbon atoms
 I am used quite often by
teachers, usually in pairs
 I am white in color
 You need water when you use
me
 I will make you feel better
 I am aspirin