AS 1.4 Bonding

Question 1

How does the VSEPR theory help us predict the shapes of molecules?

Answer 1

Count the number of lone pairs and bonding pairs around the central atom, this helps to provide the general shape of the molecule.

Question 2

2 electron pairs

Answer 2

Linear

180°

Question 3

3 electron pairs

Answer 3

Trigonal planar

120°

Question 4

4 electron pairs

Answer 4

Tetrahedral

109.5°

Question 5

5 electron pairs

Answer 5

Trigonal bipyramid

90°/120°

Question 6

6 electron pairs

Answer 6

Octahedral

90°

Question 7

How strong is hydrogen bonding?

Answer 7

The strongest of the intermolecular forces
Much stronger than Van der Waals forces
Much weaker that covalent or ionic bonds

Question 8

What elements are needed to form hydrogen bonds?

Answer 8

Fluorine, oxygen and nitrogen

-Atoms with high electronegativities and lone pairs

Question 9

Hydrogen bonding in water

Answer 9

There is attraction between the oxygen of one molecule and one of the hydrogens of two other molecules.
The small size of the hydrogen atom allows the two of them to closely approach the oxygen, forming strong bonds and a tetrahedral hydrogen-bonded structure.
The site of attraction to the oxygen atom are the two lone pairs.

Question 10

Effect of hydrogen bonding on boiling points

Answer 10

A general increase down a group as intermolecular forces increase.
Groups 5,6 and 7 the pattern is completely broken due to the presence of nitrogen, oxygen and fluorine at the top of these groups.
The hydrogen bonding within these molecules forces the boiling points to be far higher than would be expected with only van der Waals forces.