Chapter 10 · Chemical Bonding
10.3Lewis Structures of Ionic Compounds: Electrons Transferred
9 min · two checks
Predict
What does the Lewis picture of NaCl show moving?
The idea
- Show electron transfer in a binary ionic compound.
- Predict how many ions of each charge are needed.
Metals with few valence electrons lose them; nonmetals with nearly eight gain them. Sodium transfers one electron to chlorine. Magnesium transfers two, one to each of two chlorines, giving MgCl₂. Aluminum transfers three. The Lewis drawing shows empty brackets on the metal cation and full octets on the anions. There is no line between Na and Cl, because the bond is the attraction of opposite charges throughout the lattice, not a shared pair.
The number of electrons lost must equal the number gained. That is the same arithmetic as writing a neutral formula. If the drawing and the formula disagree, one of them dropped an ion. Ionic Lewis structures are a poor picture for covalent molecules; do not draw water as H⁺ and O²⁻.
Keep these
- Transfer, then draw ions. Do not draw a shared pair for NaCl.
- Electrons lost equal electrons gained.
- The formula’s subscripts match the ion count in the drawing.