1. Atoms

2. Atoms Elements are made of individual particles called atoms
Every atom is made of 3 parts:
Protons
Neutrons
Electrons

3. Atoms (cont.) Protons: positive charge Nucleus
Neutrons: neutral, no charge
Electrons: negative charge
Travel around the nucleus, creating a cloud
Nucleus

4. Protons
All atoms have a specific number
Identifies the element
Change the number, change the element
Proton # = Atomic #
Shown on periodic table

5. Add them together = atomic mass Use atomic # to find # of protons
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Protons and Neutrons
Add them together = atomic mass
Use atomic # to find # of protons
Use atomic mass to find number of neutrons

6. # of electrons = # of protons
Electrons are so small, they do not really contribute to the mass

7. Bohr suggested that electrons orbit the nucleus in levels
Bohr Model
Bohr suggested that electrons orbit the nucleus in levels
This is not technically correct. It is used more as a representation.

8. Another view

9. Energy Levels First level = 2 electrons Second level = 8 electrons
Third level = 18 electrons
Fourth level = 32 electrons
Outer level has greatest effect on properties - called Valence electrons
Outer level can never have more than 8 electrons

10. Chemical symbols used to represent elements First letter = CAP
Second letter = lower case

11. Same element - different number of neutrons Changes the atomic mass
Isotopes
Same element - different number of neutrons
Changes the atomic mass

12. Example of Isotopes - Carbon