Lewis Dot Symbols: Represent valence electrons of atoms/ions. Main group elements: valence electrons = group number; transition metals: variable valence electrons.

Drawing Lewis Dot Symbols: Place one valence electron on each side of the element symbol before pairing. For ions, add or remove electrons as needed.

Ionic Bonding: Involves transfer of electrons from metals (lose electrons, form cations) to nonmetals (gain electrons, form anions). Ionic bonds lower the energy of the system.

Covalent Bonding: Involves sharing of valence electrons between nonmetals. Each covalent bond represents a shared pair of electrons.

Metallic Bonding: Involves free-flowing valence electrons among a lattice of metal ions, giving rise to properties like conductivity, malleability, and luster.

Electronegativity: Measures an atom's ability to attract electrons. Increases across a period and up a group. Difference in electronegativity determines bond polarity.

Dipole Moment: Arises from significant differences in electronegativity between bonded atoms, resulting in polar bonds and molecular polarity.

Bond Classifications:

• Nonpolar covalent: Small or zero electronegativity difference.

• Polar covalent: Intermediate difference.

• Ionic: Large difference.

Octet Rule: Main group elements tend to achieve 8 valence electrons (octet) through bonding. Some elements can have incomplete or expanded octets.

Formal Charge: Formal Charge=Valence Electrons−(Nonbonding Electrons+Bonds) Used to determine the most stable Lewis structure; sum of formal charges equals the molecule's net charge.

Drawing Lewis Structures:

• Count total valence electrons.

• Arrange atoms (least electronegative in center, H never in center).

• Connect with single bonds, complete octets, add multiple bonds if needed.

• Assign formal charges to check stability.

Lone Pairs: Nonbonding pairs of electrons on an atom, not involved in bonding.

Sigma (σ) and Pi (π) Bonds:

• Sigma: First bond between two atoms, strongest type.

• Pi: Additional bonds in double/triple bonds, weaker than sigma.

• More pi bonds = shorter, stronger overall bond.

Special Cases:

• Incomplete Octet: Some elements (e.g., Be, B) stable with fewer than 8 electrons.

• Expanded Octet: Elements in period 3 or higher can have more than 8 electrons.

• Free Radicals: Molecules/ions with unpaired electrons, often highly reactive.

Practice Problems: Include drawing Lewis structures for atoms, ions, and molecules; determining formal charges; identifying bond types and polarity; and counting sigma/pi bonds and lone pairs.