VSEPR Theory, Polarity, and using Electronegativity Ch. 16 Covalent Bonding VSEPR Theory, Polarity, and using Electronegativity

Covalent Bonds F F F F F F A. Types of Covalent Bonds Forms when 2 atoms share a pair of valence e- A. Types of Covalent Bonds 1. Single Covalent Bond – two atoms share one pair of electrons Ex: F2 Unshared pair – e- not shared between atoms ● ● ● ● ● ● ● ● ● ● ● ● F F F F ● ● ● ● ● ● F F ● ● ● ● ● ● ● ● or ● ● ● ● ● ● ● ● ● ● ● ● ● ● What makes this bonding work? Atoms have 8 e- in their outer level to make them stable

Covalent Bonds (cont.) H H H H H H Ex: H2 ● H H H ● ● or ● Why does H2 only need 2 e- to be stable? first energy level only contains 2 e-

Covalent Bonds (cont.) O O O O O O 2. Double Covalent Bond – 2 pairs of electrons are shared between atoms Ex: O2 ● ● ● ● ● ● ● ● O O O O O O ● ● ● ● ● ● or ● ● ● ● ● ● ● ● ● ●

Covalent Bonds (cont.) N N N N N N 3. Triple Covalent Bond – 3 pairs of electrons are shared between atoms Ex: N2 ● ● ● ● N N N ● ● N N N ● ● ● ● ● ● ● ● ● ● or ● ● ● ● ● ● ● ●

Covalent Lewis Dot Structures 1. Determine the # of valence e- in each atom in the molecule (# valence e- = roman numeral for group A atoms) 2. The central atom is often the first atom written & is usually the atom with the least # of e-. (Exception – H can’t be the central atom). This is going to be the atom that needs to share the most electrons.

Lewis Dot Structures for Compounds 3. Place the electrons around the atoms so each is stable (8 around it, except H – only 2) Examples: 1. Br2 ● ● ● ● ● ● ● Br Br Br Br ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ●

N N H H H H H H O C O C O O 2. NH3 3. CO2 ● ● ● ● ● ● ● ● ● ● ● ● ● ●

C C Cl Cl Cl Cl Cl Cl Cl Cl H H O O H H 4. CCl4 5. H2O ● ● ● ● ● ● ● ●

Covalent Bond Practice Problems: 1. CH4 4. OF2 2. H2 5. CHI3 3. PH3 6. CO2

VSEPR Theory Explains the shapes of molecules. The VSEPR theory states: b/c electrons repel each other, molecules adjust their shapes so that the valence e- pairs are as far apart from each other as possible.

Shape Formula Bond Angle Electrons Linear AX2 180o 4 shared 0 unshared Bent 105o 2 shared 2 unshared Trigonal Pyramidal AX3 107o 3 shared 1 unshared Tetrahedral AX4 109.5o Trigonal Planar 120o Contains a double bond

Bond Polarity Polar Covalent Bond – when 2 atoms are joined by a covalent bond and the bonding electrons are not shared equally

Bond Polarity (cont.) Nonpolar Covalent Bond – when 2 atoms are joined by a covalent bond and the bonding electrons are shared equally

Differences between polar, nonpolar, and ionic bonds

How do you determine if a bond is polar, nonpolar, or ionic? Subtract the electronegativities of the bonding atoms (p. 405 in textbook)

Electronegativity Differences & Bond Type Type of Bond Electronegativity Difference Range Nonpolar Covalent Bond 0.0 – 0.4 Polar Covalent Bond 0.5 – 2.0 Ionic Bond greater than 2.0

3. Potassium and Chlorine 4. Fluorine and Fluorine Tell if the bonds between the following atoms are polar, nonpolar, or ionic: 1. Hydrogen and Carbon 2. Oxygen and Carbon 3. Potassium and Chlorine 4. Fluorine and Fluorine 5. Nitrogen and Oxygen H 2.1 C 2.5 0.4 Nonpolar O 3.5 C 2.5 1.0 Polar K 0.8 Cl 3.0 2.2 Ionic F 4.0 0.0 Nonpolar N 3.0 O 3.5 0.5 Polar

Polarity of Molecule Polar Molecule – a molecule with a positive and negative end. Polar bonds must be present.

Polarity of Molecule (cont.) It is possible to have polar bonds but not a polar molecule! Carbon dioxide has 2 polar bonds and is linear. Bond polarities cancel out b/c they are in opposite directions. Carbon Oxygen Oxygen

Practice: Write the dot structure of the following molecules – then predict the shape and polarity I2 PCl3 H2S CHI3 SiO2 CH2O