Formal Charge Formal Charge

What is it?
Hypochlorous acid: HOCl or HClO? Formal charge = Group number - [LPE+ ½ (BE)]
ClO - LPE: lone pair electrons BE: number of bonding electrons

Examples:
Hydrogen cyanide: HNC or HCN? i) H 2O

- ii) OH -
CN

Formal Charge Bond Polarity and Electronegativity

Formal charge and resonance structures

- i) NO 3

ii) CH COO - 3 i) Both men are equally strong ii) Both men are equally weak No one will win

iii) One is stronger than the other The stronger will win

1 Bond Polarity and Electronegativity Bond Polarity and Electronegativity

Bond polarity increase as the value of ∆χ increase
Covalent bonding between two identical atoms
∆χ : difference in electronegativity values between the H2 (χχχH = 2.2 ) Non-polar covalent bonded atoms ∆χ
Covalent bonding between two non- H2 0.0 non-polar covalent (∆χ = 0) identical atoms HF ( χχχH = 2.2, χχχF = 4.0 ) HF 1.8 polar covalent (0 < ∆χ <2.0)

Ionic bonding: LiF Polar covalent LF 3.0 ionic (∆χ >2.0)

χχχLi = 1.0, χχχF = 4.0

δ- : Partial negative charge
Bond polarity order for hydrogen halides: δ+ : Partial positive charge Ionic HF ( ∆χ = 1.8) > HCl ( ∆χ = 1.0) > HBr (∆χ = 0.8) > HI ( ∆χ = 0.5)

Bond Polarity Molecule Polarity

Use electronegativity values to classify the bonding
We can use the polarity of individual bonds to predict in the following molecules (ionic, polar covalent, or the polarity of overall molecules nonpolar covalent)
Polar Molecule = a molecule that contains
KF polarized bonds AND has the resulting partial charges distributed unsymmetrically

NO + δ δ− H O
SiCl δ+ 4 H

K O Polarity induces a dipole or a separation of 2 charge

2 Molecule Polarity and Dipole Moment Molecule Polarity
Nonpolar molecule = a molecule that has nonpolar bonds (like H 2 or I 2) or a molecule that has polarized bonds AND has the resulting partial charges distributed symmetrically δ- δ+ δ-
CO 2 O CO

- δδδ F

+
BF 3 δδδ+ δδδ
A quantitative measure of the degree of charge separation in a B δδδ- molecule. F δδδ+ F
Product of partial charges and the distance by which they are δδδ- separated.
Dipoles cancel out (point in opposite directions)
Unit : Debye (D); 1 D = 3.34 x 10 -30 C.m) resulting in a nonpolar molecule
A vector quantity, having both a magnitude and a direction

Molecule Polarity Molecule Polarity

Polar or non-polar? Polar or non-polar?

CO 2
BF 3

H O 2
NH 3

Trigonal planar Trigonal pyramidal

3 Molecule Polarity Molecule Polarity

More examples:
CS 2 – polar or nonpolar?

CCl 4 – polar or nonpolar?

SF 6 – polar or nonpolar?

Molecule Polarity Molecule Polarity

NH 3 – polar or nonpolar?
SCl 2 – polar or nonpolar?

SO 3 – polar or nonpolar?
SF 4 – polar or nonpolar?

SO 2Cl 2 – polar or nonpolar?
XeF 4 – polar or nonpolar?

4 Bond Order, Length, Energy Naming Covalent Molecules
General rules
Bond order
Make sure the compound qualifies as a covalent molecule (and not ionic)
Give the name of the least electronegative element first
Give the stem name of the more electronegative element, ending with “ide”
Indicate the number of each type of atom by the
Bond length prefixes, mono, di, tri, tetra, penta, etc.

PCl 5 phosphorus pentachloride

SO 2 sulfur dioxide

N2O dinitrogen monoxide
CO carbon monoxide

CO 2 carbon dioxide

Naming Covalent Molecules Naming Covalent Molecules

CCl 4
Diphosphorus pentoxide

NO
Sulfur trioxide

SeF 4
Silicon tetrachloride

S O 2 7
Trihydrogen nitride

CaCl 2
Dihydrogen monoxide

N2O4

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