1. The Basic Unit of Matter
The Atom
The Basic Unit of Matter

2. The Nature of Matter Elements are made of atoms
Elements are the basic substance from which all things are made

3. History of the Atom Democritus (400 B.C.) John Dalton (1808)
Identified the “atomos” means uncut
John Dalton (1808)
His theory states:
All matter is composed of atoms
Atoms cannot be divided, created or destroyed but combine to form compounds

4. The subatomic particles…
Proton  Positively charged found inside the nucleus of an atom (p+)
Have a charge of +1
Mass = 1 amu
ALWAYS the same number as the atomic number

5. The subatomic particles…
Neutron  neutral particles also found inside the nucleus of an atom (n0)
Have a charge of 0 (neutral)
Mass = 1 amu
Must calculate # of neutrons
Atomic Mass (rounded to nearest #)
# of protons (atomic number)
# of neutrons

6. The subatomic particles…
Electron  negatively charged that form a shell around the atom
found outside the nucleus of an atom (e-)
Have a charge of -1
Have a negligible (almost nothing) mass

7. Are you Bohr’ed yet? Niels Bohr (1913)
Discovered that e- orbit the nucleus in different energy levels
Must fill the LOWEST energy level first BEFORE moving to the next
1st energy level = 2 e-
2nd energy level = 8 e-
3rd energy level = 8 e-
4th energy level = 18 e- + _