Transcript - Lewis structures and bonds
- 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 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.
The shape of a molecule of CO 2 is linear.
The shape of a molecule of HCN is linear.
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
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.
H 2 O is a polar molecule.
2 H• + O
H:O:H