Unit 8 - Covalent Bonding

Covalent bonds

formed when a non-metal shares electrons with another non-metal; can be solid, liquid, or gas

Ex: CO₂

Covalent compounds physical properties

• Solid, liquid, or gas at room temp

• Low melting points

• A few are network solids - substance made up of an array of repeating covalently bonded atoms (like a diamond or quartz)

• Non-electrolytes

When a covalent bond is put into water…

it dissolves; C₆H₁₂O₆(s) —> C₆H₁₂O₆(aq)

7 diatomic molecules

 H₂, N₂, F₂, O₂,  I₂, Cl₂, Br₂ (examples of non-polar covalent bonds)

Prefixes for naming

1. mono

2. di

3. tri

4. tetra

5. penta

6. hexa

7. hepta

8. octa

9. nona

10. deca

Common covalent compounds

•  CH₄ - methane

• H₂O - water

• NH₃ - ammonia

Double bonds just count as…

"1 bonding area"

HONC Rule

explains the number of times each atom is connected to other atoms

• Hydrogen and halogens form 1 bond

• Oxygen and sulfur form 2 bonds

• Nitrogen and Phosphorus form 3 bonds

• Carbon and silicon form 4 bonds

Intermolecular forces

• Dispersion - weakest, caused by temporary dipoles, both polar and nonpolar, found in gas at STP

• Dipole–Dipole - medium strength, formed due to permanent dipoles, polar molecules only, found in liquid at STP

• Hydrogen Bonding - strongest attraction and therefore highest boiling point, hydrogen bonded to F, O, or N, found in solid at STP

Electronegativity difference

The degree to which an atom attracts electrons in a chemical bond is described by electronegativity

• Non-polar covalent (0.0-0.4)

• Polar covalent (0.5-1.8)

• Ionic (>1.8)

VSEPR

Valence Shell Electron Pair Repulsion, electrons repel each other, predicts shape of molecule

Linear (no central atom)

• diatomic

• No angle bc no central atom

• non-polar if atoms are same (O₂, N₂, Br₂)

• polar if atoms are different (HCl)

Linear

• 2 shared, 0 unshared

• Double and triple bonds count as 1 shared pair

• 180˚

• Non-polar if bonded atoms are the same (CO₂)

• Polar if bonded atoms are different (HCN)

Trigonal planar

• 3 shared, 0 unshared

• 120˚

• Non-polar if bonded atoms are the same (BF₃)

• Polar if bonded atoms are different (HCOH)

Tetrahedral

• 4 shared, 0 unshared

• Bc molecule is 3D, angle is 109˚

• Non-polar if bonded atoms are the same (CH₄)

• Polar if bonded atoms are different (CH₃F)

Bent

• 2 shared, 2 unshared

• 105˚

• Not symmetrical so it is always polar (H₂O or H₂S)

Pyramidal

• 3 shared, 1 unshared

• 107˚

• Not symmetrical so it is always polar (NH₃ or PH₃)