How do you write ionic formulas for binary compounds?

1 Answer

The term binary means two pieces. Binary compounds contain two elements.

  • Lets take the ionic formula for Calcium Chloride is CaCl2

Calcium is an Alkaline Earth Metal in the second column of the periodic table. This means that calcium has 2 valence electrons it readily gives away in order to seek the stability of the octet. This makes calcium a Ca+2 cation.

  • Chlorine is a Halogen in the 17th column or p5 group.
    Chlorine has 7 valence electrons. It needs one electron to make it stable at 8 electrons in its valence shells. This makes chlorine a Cl anion.

Ionic bonds form when the charges between the metal cation and non-metal anion are equal and opposite. This means that two Cl anions will balance with one Ca2+ cation.

  • This makes the formula for calcium chloride, CaCl2.

For the example Aluminum Oxide Al2O3

  • Aluminium has an oxidation state of +3 or Al3+
    Oxygen has an oxidation state of -2 or O2

The common multiple of 2 and 3 is 6.

  • We will need 2 aluminum atoms to get a +6 charge and 3 oxygen atoms to get a -6 charge. When the charges are equal and opposite the atoms will bond as Al2O3.

I hope this is helpful.
SMARTERTEACHER