1. ATOMS AND ION FORMATION
stable atom:
unreactive, at rest
a state likely to be found in nature
has 8 valence e–
outer shell e–
like a noble gas (8 e– = stable!)
opposite = reactive or unstable

2. VALENCE ELECTRONS number of valence e– = group #
Li and Na – 1 valence electron
Mg and Ca –
O and S –

3. FORMATION OF IONS
Atoms lose or gain e– to achieve a noble gas configuration
Once e– are gained/lost, a charge exists (positive or negative)
Charged particles are called IONS

4. POSITIVE IONS: CATIONS
formed by metals
lose electrons to achieve noble gas configuration
charge of the cation = group #
example: lithium ion = 1+
aluminum ion =
barium ion =

5. POSITIVE IONS: CATIONS

6. NEGATIVE IONS: ANIONS formed by nonmetals
gain electrons to achieve noble gas configuration
charge of the anion = group# – 8
oxide anion = 6 – 8 = 2–
N (nitride) anion =

7. NEGATIVE IONS: ANIONS

8. ANIONS vs. CATIONS ANIONS end in -ide ex: bromide, oxide, sulfide
bromide anion = Br1–
oxide anion = O2–
always larger than the atom from which it was formed

9. ANIONS VS. CATIONS CATIONS have the same name as the element
ex: sodium cation, Na magnesium ion, Mg2+
always smaller than the atom from which it was formed