Chemical Bonding: The Covalent Bond

Key Differences between Ionic and Covalent Bonding:
- Ionic bonds form between a metal (or polyatomic ion) and a nonmetal (or polyatomic ion); involve electron transfer.
- Covalent bonds usually form between two nonmetals; involve electron sharing.
- Covalent Bond: A chemical bond resulting from two nuclei attracting the same shared electrons.
Ionic compounds do not contain discrete molecules (have ions); covalent compounds have molecules as basic structural units.
Ionic compounds are solids at room temperature; covalent compounds are varied in states.
Soluble ionic solids form conducting aqueous solutions; soluble covalent compounds usually produce non-conducting aqueous solutions.
Electron sharing occurs when electron orbitals from two different atoms overlap, leading to increased stability.

Shared electrons contribute to each atom achieving a noble-gas configuration (e.g., H achieves He config with 2 electrons).
Lewis symbol (e.g., H) represents an atom; each dot represents one valence electron.

Bonding electrons: Valence electrons shared between atoms in a covalent bond.
- Represented by a dash or dots between atoms; each dash represents 2 electrons, each dot represents 1 electron.
Non-bonding electrons (Lone pairs): Valence electrons not shared between atoms; also called unshared electron pairs.

Single Covalent Bond: Two atoms share one pair of electrons (e.g., H–H in H_2).
Double Covalent Bond: Two atoms share two pairs of electrons (e.g., O=C=O in CO_2).
Triple Covalent Bond: Two atoms share three pairs of electrons (e.g., N≡N in N_2).

Nonmetallic atoms tend to form a specific number of covalent bonds.
The number of bonds formed equals the number of electrons needed to achieve an octet (noble gas configuration).
- Oxygen (6 valence electrons) forms 2 bonds.
- Nitrogen (5 valence electrons) forms 3 bonds.
- Carbon (4 valence electrons) forms 4 bonds.

A covalent bond in which both electrons of a shared pair come from only one of the two atoms involved.
Allows an atom to share nonbonding electrons from another atom to achieve a full octet.
In a regular covalent bond, each atom supplies one electron to the bond.

Lewis Structure: Diagrams showing bonding between atoms and lone pairs of electrons.
Steps for Writing Lewis Structures:
1. Calculate total valence electrons: Sum valence electrons for all atoms.
2. Arrange atoms and place single bonds: Write chemical symbols, determine central atom (usually appears once or is Carbon), and place single covalent bonds (each 2 electrons) between bonded atoms.
3. Add nonbonding electron pairs to outer atoms: Give each outer atom a full octet (8 electrons), except Hydrogen (2 electrons).
4. Place any remaining electrons on the central atom.
5. Form multiple bonds if needed: If the central atom lacks an octet, use one or more nonbonding pairs from outer atoms to form double or triple bonds.
6. Final Checks:
  - Total number of electrons in the structure equals the calculated total valence electrons.
  - Each atom (except Hydrogen) in the structure has a stable octet.

Covalent bonding exists within the polyatomic ion.
Ionic bonding exists between the polyatomic ion and ions of opposite charge.
Polyatomic ion charge is associated with the ion as a whole, not localized on a particular atom.
Use brackets ([]) to enclose the polyatomic ion, with the ionic charge shown outside.