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Formal Charge
What is it?
Formal charge = Group number - [LPE+ ½ (BE)]
LPE: lone pair electrons BE: number of bonding electrons
Examples:
i) H 2 O
ii) OH-
Hypochlorous acid: HOCl or HClO?
ClO-
Hydrogen cyanide: HNC or HCN?
CN-
Formal Charge
Formal Charge
Formal charge and resonance structures
i) NO 3 -
ii) CH 3 COO- i) Both men are equally strong ii) Both men are equally weak
iii) One is stronger than the other
No one will win
The stronger will win
Bond Polarity and Electronegativity
Bond Polarity and Electronegativity
Covalent bonding between two identical atoms H 2 ( χχχχ H = 2.2)
Covalent bonding between two non- identical atoms HF ( χχχχ H = 2.2, χχχχ F = 4.0)
δ-^ : Partial negative charge δ+^ : Partial positive charge
Ionic bonding: LiF
χχχχ Li = 1.0, χχχχ F = 4.
Non-polar covalent
Polar covalent
Ionic
Bond polarity increase as the value of ∆χ increase
∆χ : difference in electronegativity values between the bonded atoms ∆χ H 2 0.0 non-polar covalent (∆χ = 0)
HF 1.8 polar covalent (0 <∆χ <2.0)
LF 3.0 ionic (∆χ >2.0)
Bond polarity order for hydrogen halides: HF (∆χ = 1.8) > HCl (∆χ = 1.0) > HBr (∆χ = 0.8) > HI (∆χ = 0.5)
Bond Polarity and Electronegativity
Bond Polarity
Use electronegativity values to classify the bonding in the following molecules (ionic, polar covalent, or nonpolar covalent) KF
NO
SiCl 4
K 2 O
Molecule Polarity
We can use the polarity of individual bonds to predict the polarity of overall molecules Polar Molecule = a molecule that contains polarized bonds AND has the resulting partial charges distributed unsymmetrically
Polarity induces a dipole or a separation of charge
H
H
O
δ+^ δ−
δ+
More examples:
Molecule Polarity Molecule Polarity
CS 2 – polar or nonpolar?
CCl 4 – polar or nonpolar?
SF 6 – polar or nonpolar?
Molecule Polarity
NH 3 – polar or nonpolar?
SO 3 – polar or nonpolar?
SO 2 Cl 2 – polar or nonpolar?
Molecule Polarity
SCl 2 – polar or nonpolar?
SF 4 – polar or nonpolar?
XeF 4 – polar or nonpolar?
Bond Order, Length, Energy
Bond order
Bond length
Naming Covalent Molecules
General rules 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 prefixes, mono, di, tri, tetra, penta, etc. PCl 5 phosphorus pentachloride SO 2 sulfur dioxide N 2 O dinitrogen monoxide CO carbon monoxide CO 2 carbon dioxide
Naming Covalent Molecules
CCl 4
NO
SeF 4
S 2 O 7
CaCl 2
N 2 O 4
Naming Covalent Molecules
Diphosphorus pentoxide
Sulfur trioxide
Silicon tetrachloride
Trihydrogen nitride
Dihydrogen monoxide
