Example #1 - ammonium ion NH4+
1. This compound is covalent.
2. Determine the total number of valence electrons available:
One nitrogen has 5 valence electrons
Four hydrogen, each with one valence electron, totals 4
The positive charge means one electron has been removed
This means there are 9 minus one = 8 valence electrons, making 4 pairs, available.
3. Organize the atoms so there is a central atom (usually the least electronegative) surrounded by ligand (outer) atoms. Hydrogen is never the central atom.
4. Determine a provisional electron distribution by arranging the electron pairs (E.P.) until all available pairs have been distributed:
5. The formal charge (F) on the central atom is zero. The structure in step 4 is the correct answer. Note the use of brackets. This indicates that the positive charge is distributed over the molecule and is not part of any given atom.
Example #2 - hydronium ion H3O+
1. This compound is covalent.
2. Determine the total number of valence electrons available:
One oxygen has 6 valence electrons
Three hydrogen, each with one valence electron, totals 3
The positive charge means one electron has been removed
This means there are 9 minus one = 8 valence electrons, making 4 pairs, available.
3. Organize the atoms so there is a central atom (usually the least electronegative) surrounded by ligand (outer) atoms. Hydrogen is never the central atom.
It does not matter which of the three sides you use to put hydrogens on.
4. Determine a provisional electron distribution by arranging the electron pairs (E.P.) until all available pairs have been distributed:
5. The formal charge (F) on the central atom is zero. The structure in step 4 is the correct answer.
Note the use of brackets.
Example #3 - nitrogen trifluoride NF3
1. This compound is covalent.
2. Determine the total number of valence electrons available:
One nitrogen has 5 valence electrons
Three fluorine, ea
