Warm-Up What is a covalent bond? What types of elements form covalent bonds?

Nonmetals Join Together Covalent Bonding Nonmetals Join Together

Covalent Bonding Covalent Bond – a bond in which two nonmetals share one or more of their valence electrons Polar – unequal sharing of electrons Nonpolar – equal sharing of electrons Smallest unit is called a molecule Common Examples: (Know these!) Diatomic elements Water (H2O) Ammonia (NH3) Methane (CH4)

Bond Polarity Unequal sharing of electrons is due to a difference in electronegativity (ΔEN) of the two atoms Ionic Bond: ΔEN ≥ 1.7 Ex: NaCl Polar Covalent Bond: 0.4 < ΔEN < 1.7 Ex: H2O Nonpolar Covalent Bond: ΔEN ≤ 0.4 Ex: CH4

Calculating ΔEN ∆EN= EN Element 1 − EN Element 2

Covalent Bond Lengths Valence electron orbitals of each element overlap as electrons are shared More shared electrons creates a shorter and stronger bond

Covalent Properties Low melting and boiling points Many are liquids and gases at room temperature Soluble in water IF they are polar (like dissolves like) Do not conduct electricity

Lewis Dot Structures Show the symbols, valence electrons, and bonds in a covalent compound Dictated by The Octet Rule (all atoms want to have 8 valence electrons) Exception: Hydrogen only needs 2 Exception: Boron can only get 6

Steps to Draw Draw out each atom with its valence electrons Move electrons to share until all atoms have full outer shells Redraw

Drawing Hints Put the single atom in the middle of the dot structure Hydrogen is NEVER in the middle of the dot structure A dash connecting two atoms represents a pair of shared electrons Sometimes, more than one pair of electrons is shared Two pairs = double bond Three pairs = triple bond Don’t forget to re-draw non-bonding electrons!

Example 1 CH4

Example 2 PCl3

Example 3 H2S

Example 4 HCl

Example 5 CO2

Example 6 BH3