Lewis

What are valence electrons?

Valence electrons are the electrons in the outermost shell of an atom that are involved in chemical bonding.

How do you determine the number of valence electrons for a neutral atom?

For main group elements (Groups 1, 2, 13-18), the number of valence electrons is equal to the atom's group number in the periodic table.

How do you calculate the total number of valence electrons for a molecule?

Add the valence electrons of all individual atoms in the molecule.

How do you adjust the total valence electron count for a polyatomic ion?

1. Multiply the number of atoms by their valence electrons and sum them up for all atoms.
2. For anions (negative charge), add electrons equal to the magnitude of the negative charge.
3. For cations (positive charge), subtract electrons equal to the magnitude of the positive charge.

Example: CO_3^{2-}

• Carbon (Group 14): 4 valence electrons
• Oxygen (Group 16): 6 valence electrons
• Total from atoms: 4 + (3 \times 6) = 22 electrons
• For 2- charge: 22 + 2 = 24 total valence electrons.