1. Introduction to Chemistry
Science 10 Unit 2

2. History Early Greeks thought matter could be subdivided forever.
~ 450 B.C. Empedocles suggested all matter was made of only 4 “elements”
earth, air, water, and fire
~ 400 B.C. Democritus suggested all matter was made of atoms, tiny particles that cannot be broken down further.
He was not believed!
1669 Hennig Brandt discovered phosphorus.
He did not realize he discovered an element!
Empedocles (Em peh de klees) – Greek philospher – all 4 elements were indestructable and could combine to form different structures
Democritus – everything is composed of atoms, space lies between atoms
Hennig Brandt – German alchemist (study transformation of matter), discovered phosphorus by heating residues of boiled down urine, produced a liquid that solidified  phosphorus!
Cavendish – first to discover hydrogen – lots of experiments yielded a “flammable gas”
Experimenters such as Robert Boyle, Henry Cavendish and Antoine Lavoisier produced gases such as oxygen and hydrogen.

3. John Dalton invented the modern atomic theory.
Elements are all made up of extremely small particles called atoms.
The atoms of the same element are all identical, while atoms of different elements will have different properties.
Each chemical compound is unique and consists of a particular combination of atoms.
Chemical reactions involve the reshuffling of atoms in a compound to make new compounds.
Dalton – English chemist
Now we know atoms can be destroyed via nuclear reactions (not chemical reactions), atoms can be broken down into smaller parts – protons, neutrons, electrons
Note: updates to Dalton’s original theory have been made as additional information was discovered.

4. Pure substances
A pure substance is a made up of only one type of particle.
There are only two types of pure substances:
Elements
Compounds
An element is a pure substance that cannot be separated into simpler substances by chemical processes.
Compound – H20 – hydrogen and oxygen
A compound is a pure substance that is composed of two or more different atoms combined in a specific way.

5. Subatomic Composition of Atoms
An atom is the smallest possible piece of an element which still has the properties of the element.
A subatomic particle is any piece of an atom.
Location
Particle
Mass
Charge
protons
neutrons
electrons
1 amu
~ 0 amu
+ 1 -1
nucleus
orbitals around nucleus
Amu = atomic mass unit

6. Bohr Model of Atomic Structure
Shows all electrons in each energy level around the atom.
Atomic number = protons
Oxygen’s atomic # = 8
8 protons 8p
Atomic mass = protons + neutrons 8n
Oxygen’s mass = 16
8 neutrons
Atomic number = protons and neutrons
Atomc mass – protons = neutrons
-neutrons and protons for atoms w/ fewer than 30 protons  after that, more neutrons than protons because repulsion between protons makes it less stable and more neutrons keep the protons further apart
Note: A neutral atom has no overall charge. protons (+) = electrons (-)
Oxygen
8 protons = +8
8 electrons (-8)

7. Assignment
Atomic Structure Worksheet