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Bond Polarity and Formal Charge: Concepts and Calculations, Study notes of Chemistry

An in-depth understanding of formal charge and bond polarity. It explains the concept of formal charge, its calculation using lone pair electrons and bonding electrons. The document also covers resonance structures and their impact on formal charge. Furthermore, it discusses electronegativity, bond polarity, and their relationship. examples of various molecules and their formal charges and bond polarities.

What you will learn

  • How does electronegativity affect bond polarity?
  • What is formal charge and how is it calculated?
  • What is the difference between polar covalent and ionic bonds?

Typology: Study notes

2021/2022

Uploaded on 09/12/2022

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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) H2O
ii) OH-
Hypochlorous acid: HOCl or HClO?
ClO-
Hydrogen cyanide: HNC or HCN?
CN-
Formal Charge
Formal Charge
Formal charge and resonance structures
i) NO3-
ii) CH3COO-
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
pf3
pf4
pf5

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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