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 #CaCl^2#

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 #17^(th)# column or #p^5# 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 #Ca^(2+)# cation.

  • This makes the formula for calcium chloride, #CaCl_2#.

For the example Aluminum Oxide #Al_2O_3#

  • Aluminium has an oxidation state of #+3# or #Al^(3+)#
    Oxygen has an oxidation state of -2 or #O^(2-)#

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 #Al_2O_3#.

I hope this is helpful.
SMARTERTEACHER