IONIC MOLECULAR STRUCTURE: Another way atoms bond
The other way that atoms can bond is by donating, or giving away electrons to another
atom. This is called ionic bonding. Look at a Na atom. It is on the far left side of the
periodic table. If it were to covalently bond it would have to find 7 electrons to share!
Instead, Na wants to give up an electron which moves it back one space in the periodic
table thus getting rid of a nuisance electron in a third shell and achieving a full valence
electron number in its lower second shell. Where does it donate this electron? It gives it
to atoms that are one space away from being all the way right on the periodic table. Look
at the column of atoms just to the left of the far column on the periodic table. These
atoms need just one electron to achieve their full number of valence electrons. So, Na
readily gives an atom to chlorine for example and these atoms thus bond ionically making
the molecule sodium chloride, or table salt! But what makes them bond? When Na gives
an electron to Cl, it is now one electron less than it would be if it were a balanced charge
neutral atom (electrons equal to protons) so we indicate with a plus sign that it is a
positively charged ion (cation) like this: Na+. And when Cl gains an electron it now has
an excess negative charge indicated with a negative sign (anion) like this: Cl-. These two
ions will be attracted to each other due to their opposite charges and bond as a molecule.
Use a periodic table to make the following ionic molecules.
1. How many O atoms does Mg need to give away its 2 electrons? Draw a molecule of
magnesium oxide (MgO) showing all the valence electrons.
2. How many Cl atoms does Ca need to donate its 2 electrons? Draw a molecule of
calcium chloride (CaCl 2) showing all the valence electrons.
3. How many K atoms does O have to find to gain 2 electrons? Draw a molecule of
potassium oxide (K20) showing all the valence electrons.
4. How many F atoms does Li need to make an ionic bond? Draw a molecule of lithium
fluoride (LiF) showing all the valence electrons.
5. How many Na atoms does O have to find to form a ionic bond? Draw a molecule of
sodium oxide (Na2O) showing all the valence electrons.
6. How many K atoms does P need to form a ionic bond? Draw an atom of potassium
phosphate (K3P) showing all the valence electrons.
7. How many Cl atoms does Ba need to form a ionic bond? Draw a molecule of
barium chloride (BaCl2) showing all the valence electrons.