Bonding

Question 1

What are the ‘classic’ three bonding models? What are they useful for

Answer 1

1) VSEPR - Valence Shell Electron Pair Repulsion
Useful mostly for predicting/explaining geometries of elements

2) Hybridisation Theory
Useful mostly for predicting/explaining geometries of elements and understanding how bonds form

3) Group Theory/MO Theory
Useful for predicting/explaining geometries of elements and understanding how bonds form

Question 2

How to determine geometries using VSEPR?

Answer 2

1) Figure out the number of coordinated atoms and hence bonding pairs of electrons (BP)
2) Find the number of lone pairs (LP) of electrons
3) Figure out the effect of the repulsion
Order of effect: LP-LP > LP-BP > BP-BP
Multiple bond > Single bond

Question 3

VESPR: H2C=C(CH3)2 angles around the central C

Answer 3

124 between C=C and C-C, 111.5 between C-C and C-C

Question 4

Determine the expected geometry of SF4?

Answer 4

See-Saw, lone pair has the most space - repulsion minimised

Question 5

Where does VSEPR break down?

Answer 5

A good example is congeners
e.g. NH3 vs PH3
NH3 107, PH3 93.5
Implication of greater stereochemical activity from the P lone pair
Cant easily explain with VSEPR
aka VSEPR is a very general

Question 6

What is the fundamental theory of VSEPR

Answer 6

-Electron pairs repel each other electrostatically(bonding pair of electrons or lone pairs or electrons)
-The groups on the considered atom arrange themselves to minimise repulsion to form the most stable arrangement of electron groups resulting in a molecular structure with lowest energy