Lewis Structures

Metallic bonding

Sharing of electrons among a lattice of positive metal ions.

Delocalised electrons

Valence electrons in metals that are free to move from one ion to another. Occurs in metallic bonding.

Lewis Theory

Atoms and ions are stable with a full valence; atoms form bonds to achieve this.

Lewis Structure Rule - Total Valence Electrons

Sum all valence electrons; adjust for charges (add for negative, subtract for positive).

Lewis Structure Rule - Central Atom

Use least electronegative atom (except hydrogen, which is always peripheral).

Lewis Structure Rule - Octet

Place electron pairs around atoms until the octet of 8 is met; hydrogen needs only 2 electrons.

Polyatomic Ions - Lewis

Enclose structure in brackets and write charge outside.

Octet Rule Exception - Expansion

Atoms in period 3+ can have more than 8 electrons due to access to d orbitals.

Octet Expansion Molecules

Phosphorus has 5 valence e- that can form as many as 5 bonds. Sulfur has 6 e- that can form as many as 6 bonds. Other examples may include: SF4, XeF2, SeF4, TeF6, XeF5.

Octet Rule Exception - Electron Deficient

Elements like Be and B may have fewer than 8 electrons (e.g., BF₃ has 6). They do not double bond and make covalent bonds.

Coordinate Covalent Bond

A bond formed when both electrons come from the same atom.

Coordinate Bond Example

NH₃ donates lone pair to H⁺ forming NH₄⁺.