Chemical Bonding: Ionic and Covalent Bonds, Lewis Structures, and Lattice Energy

Chemical Bonding

Introduction to Chemical Bonding

Chemical bonding describes the forces that hold atoms together in compounds. The two primary types of chemical bonds are ionic bonds and covalent bonds. Understanding these bonds is fundamental to predicting the properties and behaviors of substances.

Ionic Bonds

• Definition: Ionic bonds form when one or more valence electrons are transferred from one atom to another, resulting in the formation of oppositely charged ions (cations and anions).

• Formation: Typically occur between a metal (which loses electrons to become a cation) and a nonmetal (which gains electrons to become an anion).

• Properties of Ionic Compounds:

  • Often called salts.

  • Dissolve readily in water.

  • Strong electrostatic forces of attraction between ions (high lattice energy).

  • Physical behavior: hard, rigid, and brittle.

  • Poor conductors of electricity in the solid state, but conduct electricity when melted or dissolved in water.

  • High melting and boiling points.

  • Vapor consists of ion pairs.

Covalent Bonds

• Definition: Covalent bonds involve the sharing of valence electrons between atoms. They form when both atoms have similar tendencies to attract electrons (similar ionization energies and electron affinities).

• Formation: Occur between two nonmetals.

• Properties of Covalent Compounds:

  • Weaker bonds compared to ionic bonds.

  • Most covalent compounds are insoluble in water.

  • Poor conductors of electricity.

Lewis Dot Structures

Lewis Symbols

The Lewis symbol for an element consists of its chemical symbol surrounded by dots representing its valence electrons. This notation, developed by Gilbert Lewis, helps visualize the valence electrons available for bonding.

Atom	Electronic Configuration	Lewis Symbol
Sodium	[Ne]3s1	Na •
Magnesium	[Ne]3s2	Mg ••
Aluminum	[Ne]3s23p1	Al •••
Silicon	[Ne]3s23p2	Si ••••
Phosphorus	[Ne]3s23p3	P •••••
Sulfur	[Ne]3s23p4	S ••••••
Chlorine	[Ne]3s23p5	Cl •••••••
Argon	[Ne]3s23p6	Ar ••••••••

Additional info: The number of dots equals the number of valence electrons for main group elements.

Lewis Structures for Ionic Compounds

• Show the transfer of electrons from the metal to the nonmetal.

• Example: Formation of NaCl

  • Na • + ••Cl:•• → Na+ + :Cl:•••••••-

• Example: Formation of LiF

  • Li: 1s22s1 → Li+ ([He] configuration)

  • F: 1s22s22p5 → F- ([Ne] configuration)

Lewis Structures for Covalent Compounds

• Show the sharing of electron pairs between atoms.

• Octet Rule: Atoms tend to form bonds so that each atom has eight electrons in its valence shell (except H and He, which have two).

• Examples:

  • H2: H• + •H → H:H

  • Cl2: :Cl:•••••• + ••••••:Cl: → :Cl:Cl:

• Bond Pair: A pair of electrons shared between two atoms (one bond = two electrons).

• Single Bond: Shares 2 electrons (e.g., H2, Cl2, CH4).

• Double Bond: Shares 4 electrons (e.g., CH2CH2, O2).

• Triple Bond: Shares 6 electrons (e.g., N2, C2H2).

• Lone Pairs: Nonbonding electrons, not involved in bonding, usually shown as dots (e.g., H2O has two lone pairs on O).