# - Lewis structures and bonds - bonding theories

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- Lewis structures and bonds - bonding theories

Lewis Structures and Bonding
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 Cl2, the total number of unshared pairs of electrons is 6.
Cl Cl  Cl―Cl or Cl:Cl The diatomic molecule N2 contains a triple covalent bond. N N  N≡N or N⋮⋮N In the N2 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 CO2. C 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.

The shape of a molecule of CO2 is linear.

The shape of a molecule of HCN is linear.

The shape of a molecule of CH4 is tetrahedral.

The shape of a molecule of NH3 is trigonal pyramidal.

The shape of a molecule of H2O 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: CH4 Bond angle = 106.5 degrees Example: NH3

Bond angle = 104.5 degrees Example: H2O Bond angle = 120 degrees Example: CO32-

Bond angle = 118.6 degrees Example: O3 Bond angle = 180 degrees Example: CO2

Intermolecular Forces
Intermolecular forces – forces between 2 molecules Van der Waals forces - weakest attractions between molecules Dipole interactions – polar molecules attracted to one another Dispersion forces – caused by the motion of electrons

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. H2O is a polar molecule. 2 H• O  H:O:H