MSE - CHAP 2

$$\frac{1}{12}$$ of the mass of a ¹²C atom

Electrons (negative elementary particle) circle the nucleus

Nucleus (diameter $$\approx$$ 10^-14m) contains most of the mass of the atom

Number of protons = Atomic number = ordinal number is the periodic table

Number of nucleons = mass number A

Atomic shell --> number of electron = number or protons --> electrically neutral

Electrons occupy discrete energy levels -> only 2 electrons at max. can have the same energy (have unequal spin - Pauli-principle)

4 quantum numbers describe the electrons in an atom