The Basic Unit of Matter The Atom The Basic Unit of Matter

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

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

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

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

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

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- + _