Drawing Lewis Structures Arrange the element symbols. Central atoms are generally those with the highest bonding capacity. Carbon atoms are always central atoms Hydrogen atoms are always peripheral atoms Add up the number of valence electrons from all atoms. For polyatomic ions, add one electron for each negative charge and subtract one for each positive charge. Draw a skeleton structure with atoms attached by single bonds. Complete the octets of peripheral atoms. Place extra electrons on the central atom. If the central atom doesn’t have an octet, try forming multiple bonds by moving lone pairs.

Quantum Mechanics and Bonding

QM to Explain Ionic Bonds Transfer of electron from one orbital to another

QM to Explain Covalent Bonds In grade 11 you noticed exceptions to the octet rule for molecular compounds A more complex understanding than simple Lewis structures is required Valence Bond Theory

Valence Bond Theory A covalent bond forms when the atomic orbitals of 2 atoms overlap to share a common region in space The region of overlap can contain a maximum of 2 electrons with opposite spins (Pauli exclusion principle) The greater the overlap, the stronger the bond. Shape of overlap depends on the shape and orientation of orbitals involved Orbital hybridization occurs when orbitals overlap and combine to form new orbitals

Single Bonds End-to-end overlap of orbitals, called sigma (σ) bonds Examples H2 HF F2

Hybridization Examples Be B C P S Br Xe

Double and Triple Bonds Side-by-side overlap of orbitals, called pi (π) bonds

Practice Valence Bond Theory Worksheet P. 232 #1-5 P. 235 #8-14