
atoms that are now stable because they have
gained or lost valence electrons resulting a
positively or negatively charged atom

a type of chemical
bond formed
between ions with
opposite charges
(+ and -)

therefore, it is
mostly elements
from the left side
of the periodic
table combining
with those from the
right side
+
-

always the same elements in the same
proportion
 ex- NaCl (1:1)
 CaCl2 (1:2)
 Al2O3 (2:3)

atoms gain or lose valence electrons in order
to have a full valence shell (2 or 8)
 ex) Na has one valence electron, therefore it
would lose it and be 1+ charged

ex) O has six valence electrons, therefore it
would gain two and be 2- charged
e-
+
-
+
-
Na gives Cl
one electron
and now both
atoms are
stable

it is easier to just draw Lewis-dot structures to
show valence electrons instead of the drawing
the whole atom


An oxidation number indicates the charge on
the atom (or ion) when electrons are lost,
gained, or shared in chemical bonds
the oxidation numbers for all the atoms in a
compound must add up to zero
1+
2+
3+
4+/- 3-
2-
1-
0
...etc.
As it turns out, atoms bond together for a very
simple reason: atoms like to have full valence
shells (2 or 8).



sometimes it takes more than one of each
atom to make the compound “work”
Mg and Cl?
it takes two chlorines to combine with
one magnesium

MgCl2 → magnesium chloride


Mg and N?
it takes two
nitrogens to
combine with
three
magnesiums


Mg3N2
magnesium
nitride

Easiest way is to switch the charge numbers
and write them as subscripts on the formula.
Be +2 and N 3Be3 N2
beryllium nitride



there is only one way ions can combine,
therefore there is only one name for each
compound formed
keep the first element’s name the same
change the second element ending to ide
 sodium and chlorine (NaCl) becomes…
 sodium chloride

magnesium and fluorine (MgF2)….
 magnesium fluoride

K and P (K3P)
 potassium phosphide