Question

How do you determine the number of electrons in the Lewis structure of a molecule? A polyatomic ion?

a) Sum of valence electrons and bond electrons
b) Difference between valence electrons and bond electrons
c) Counting only valence electrons
d) Counting only bond electrons

Answer 1

To determine the number of electrons in the Lewis structure of a molecule or polyatomic ion, you need to first determine the total number of valence electrons. Then, count the number of regions of electron density around the central atom. Finally, place bonding pairs of electrons and distribute the remaining electrons as lone pairs.

Step-by-step explanation:

1. Determine the total number of valence electrons in the molecule or ion. Add together the valence electrons from each atom. If the species is a polyatomic ion, remember to add or subtract the number of electrons necessary to give the total charge on the ion.
2. Count the number of regions of electron density (lone pairs and bonds) around the central atom. A single, double, or triple bond counts as one region of electron density.
3. Place a bonding pair of electrons between each pair of adjacent atoms to give a single bond.
4. Distribute the remaining electrons as lone pairs on the terminal atoms, completing an octet.