Lewis Dot Symbols: Represent valence electrons of atoms or 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 (which lose electrons) to nonmetals (which gain electrons), forming cations and anions. Ionic bonds lower the energy of the system.

Covalent Bonding: Involves sharing of valence electrons between nonmetals. Atoms achieve stable octets by sharing electrons.

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

Electronegativity (EN): Measures an atom's ability to attract electrons. EN increases across a period and up a group. The difference in EN between atoms determines bond polarity.

Dipole Moment: Arises from significant EN differences, creating partial charges and a dipole arrow pointing toward the more electronegative atom.

Chemical Bond Classifications:

• Nonpolar covalent: EN difference ≈ 0

• Polar covalent: Small to intermediate EN difference

• Ionic: Large EN difference

Octet Rule: Main group elements tend to achieve 8 valence electrons.

• Incomplete octet: Fewer than 8 electrons (e.g., Be, B)

• Expanded octet: More than 8 electrons (elements in period 3 and below)

Formal Charge: Used to determine the most stable Lewis structure. Formal Charge=Valence Electrons−(Nonbonding Electrons+Bonds)

Best Lewis Structure: Minimizes formal charges and places negative charges on more electronegative atoms.

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

Sigma (σ) and Pi (π) Bonds:

• Sigma bond: Direct overlap, strongest type, present in all single bonds.

• Pi bond: Sideways overlap, present in double and triple bonds (double = 1 σ + 1 π, triple = 1 σ + 2 π).

• Bond strength increases and bond length decreases with more shared electrons (triple > double > single).

Lewis Structures for Ions and Ionic Compounds: Draw ions separately, showing their charges, and arrange to reflect electrostatic attraction.

Radicals: Molecules or ions with an unpaired electron. Place the unpaired electron on the atom with the lowest formal charge.