SL Chem - Unit #1: Covalent Bonding

Molecular Compounds

They’re made up of non-metals that are bonded together with a covalent bond where the electrons are shared between both atoms

• Have an electronegativity difference of <1.7

Molecules

The name for atoms in a covalent bond

Molecular Compounds form by the…

Electrostatic attraction between the nuclei and the shared electron pairs

Drawing Covalent Compounds

1. Draw the element with the lowest # of valence electrons (or lowest electronegativity) in the middle and the other atoms go around it

2. Make sure all atoms have a stable octet if not you can make double/triple bonds to make them stable

Relationship between # of bonds, their strength and their length

The more bonds between molecules the stronger the bond

• Stronger bonds are shorter and vice versa

Some examples…

1. Nitrogen₂: Triple bond - strongest- shortest

2. Oxygen₂: Double bond

3. Hydrogen₂: Single bond- weakest - shortest

Resonance

The actual structure of a molecule is a composite/ average (like a possibility) of the number (different variations) of lewis structures that can be drawn

Resonance Structures

Every single Lewis structure that can be drawn

• If you’re in a scenario where you can choose between multiple possibilities to make the stable octet it’s a resonance structure

Octet Rule

In some covalent bonds we can reach a stable octet with less/more than 8 electrons in the valence shell

Expanded Octet

• If there are more than 8 electrons in the third valence shell for elements in the 3rd or beyond periods

Common elements that follow the octet rule (4)

Boron, Phosphor, Sulfur and Beryllium

Coordinate (Dative) Covalent Bonds

A covalent bond where one molecule will share two of its own electrons to make a shared bond with the other molecule

• Shows using arrows rather than a line