Untitled - Kelly Walsh High School

20 CHEMISTRY FOR THE UTTERLY CONFUSED
Don’t Forget!
Don’t Forget!
electrons. Ions are formed. An ion is an atom or group of atoms that has a charge
due to the loss or gain of electrons. If the atom loses electrons, it is left with a positive
charge due to having more protons (positive charges) than electrons (negative
charges). Ions with a positive charge are cations. If the atom gains electrons,
it now has more electrons (negative charges) than protons (positive charges) and
it is left with a negative charge. Ions with negative charges are anions.
Atoms of the main group or representative elements tend to lose or gain
enough electrons to achieve the same number of electrons as the noble gas closest
to the element’s atomic number. The alkali metals all tend to lose one electron.
For example, sodium and potassium metals would lose a single electron
each to form Na and K . The alkaline earth metals lose two electrons.
Magnesium and calcium would each lose two electrons to form Mg 2 and Ca 2 .
(Ca and Ca 2 are not the same; these formulas refer to the element and ion
respectively.) The halogens all tend to gain one electron. Therefore fluorine and
chlorine would form F and Cl . Oxygen would form O 2 .
Metals tend to lose electrons to form cations while nonmetals tend to gain electrons
to form anions.
Sometimes groups of atoms may possess a charge and behave as ions. We call
these chemical species polyatomic ions. Examples include the ammonium ion,
NH 4 , the nitrate ion, NO3 , and the bicarbonate ion, HCO3 .
Since opposite charges attract each other, the cations attract the anions, forming
an ionic compound. Ionic compounds are neutral so that the number of positive
charges would equal the number of negative charges. The potassium cation
would attract the chloride anion to form the ionic compound potassium chloride,
KCl. We call ionic compounds such as this salts.
In an ionic compound there must be the same number of positive and negative
charges. All compounds are neutral.