Writing Lewis Structures for Covalent Compounds

2. Calculate the total number of electrons for the Lewis structure by summing the valence electrons of each atom in the molecule.

• The number of valence electrons for any main-group element is equal to its group number in the periodic table.
• If you are writing a Lewis structure for a polyatomic ion, the charge of the ion must be considered when calculating the total number of electrons.
• Add one electron for each negative charge and subtract one electron for each positive charge.