


atoms held together by attractive forces
atoms bond when their valence electrons
interact
always the same elements in the same
proportion
 ex- NaCl (1:1)
 CaCl2 (1:2)
 Al2O3 (2:3)

formed between
atoms with
opposite charges
(+ and -)

therefore, it is
mostly elements
from the left side
of the periodic
table combining
with those from the
right side
+
-

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 (this is
referred to as its ionic charge)

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
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 becomes…
 sodium chloride

Mg and Fl
 magnesium fluoride

K and P
 potassium phosphide