Untitled - Kelly Walsh High School

24 CHEMISTRY FOR THE UTTERLY CONFUSED
on the periodic table are metals.) Metals may combine with nonmetals or with
polyatomic ions. We will begin with binary compounds containing metals. The
naming of a metal/nonmetal compound is similar to naming molecular compounds
except that you do not use prefixes. (There are a few archaic names,
which do include prefixes in their name. Your instructor will let you know
which, if any, of these you will need to learn.) In these compounds, the cation
will always appear first in both the name and the formula.
Without using prefixes, we need another method of determining the number of
each type of atom present. This method depends on the charges of each ion. We
can predict the charge of the ion from the element’s position on the periodic
table. Unfortunately, this method does not work very well for the transition elements,
so we will save a discussion of transition metal compounds until later.
For the main group or representative elements, we simply find the charges of
the cations by counting from left to right on the periodic table, skipping the
transition metals.
If we locate the metals from our list on the periodic table, we see:
Na Mg Al
K Ca
Sodium and potassium are in the first column, so they, and any other metal in
this column, should form a cation with a 1 charge. Magnesium and calcium
are in the second column, thus they, and any other metal in the same column,
should form a cation with a 2 charge. Aluminum is in the third column (skipping
the transition metals), so that aluminum, and any other metal in the same
column, should form a cation with a 3 charge. Thus, the cations of these five
metals are: Na , K , Mg 2 , Ca 2 , and Al 3 .
Nonmetals are the opposite of metals. Thus, while metals give cations (positive
ions); nonmetals will yield anions (negative ions), which are the opposite of
cations. We can predict the charge on an anion from the position of the nonmetal
on the periodic table. Since nonmetals are the opposite of metals, we will
need to count in the opposite direction. The noble gases are zero. The next column
to the left will be 1, then 2, and then 3. The nonmetals on our list
should form the following anions:
N 3 O 2 F
S 2 Cl
Ions always have charges; compounds never have charges. How can we combine
charged ions and end up with no charge? The answer: add equal numbers
of positive and negative charges. The sum of equal numbers of positive charges