- LEWIS STRUCTURES AND BONDS - BONDING THEORIES

Lewis Structures and Bonding

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Use NASB to draw dot diagrams. N – electrons needed to fill valence (8 or 2) A- electrons available in atom S – electrons shared = N – A B – formed bonds (S divided by 2)

    

In Cl 2 , the total number of unshared pairs of electrons is 6.

Cl + Cl



Cl―Cl or Cl:Cl The diatomic molecule N covalent bond.

N + N



N

≡

2 contains a triple N or N

⋮⋮

N In the N 2 molecule, there is only one unshared pair of electrons in each nitrogen atom.



The HI molecule contains only one single covalent bond.



H• + I



H―I or H:I



There are 2 double covalent bonds in a molecule of CO 2 .



C 2 O



O ═ C ═ O or O::C::O



Carbon monoxide has a triple covalent bond. C O



C ≡ O OR C

⋮⋮

O

Bonding Theories



According to VSEPR theory, molecules adjust their shapes to keep pairs of valence electrons as far apart as possible.

 VSEPR –  Valence Shell Electron Pair Repulsion 

A stereoactive set is a shared pair or an unshared pair of electrons around the central atom.

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The shape of a molecule of CO 2 is linear.

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The shape of a molecule of HCN is linear.

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The shape of a molecule of CH 4 tetrahedral.

is



The shape of a molecule of NH 3 pyramidal.

is trigonal



The shape of a molecule of H 2 O is bent.



According to VSEPR theory repulsive forces between unshared pairs of electrons causes water molecules to have their shape.

Bond angle = 109.5 degrees Example: CH 4 Bond angle = 106.5 degrees Example: NH 3

Bond angle = 104.5 degrees Example: H 2 O Bond angle = 120 degrees Example: CO 3 2-

Bond angle = 118.6 degrees Example: O 3 Bond angle = 180 degrees Example: CO 2

Intermolecular Forces

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Intermolecular forces – forces between 2 molecules Van der Waals forces - weakest attractions between molecules

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Dipole interactions – polar molecules attracted to one another Dispersion forces – caused by the motion of electrons

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Hydrogen bonds – strongest intermolecular forces Hydrogen covalently bonded to a very electronegative atom is also bonded to an unshared electron pair of another electronegative atom.

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H 2 O is a polar molecule.



2 H• + O



H:O:H