6. SHAPES OF MOLECULES AND INTERMOLECULAR FORCES

Question 1

Electron pairs repel one another so…

Answer 1

that they are arranged as far apart as possible.
This minimises repulsion and thus holds the bonded atoms in a definite shape.

Question 2

Do lone pairs or bonded pairs have greater repulsion and why?

Answer 2

Lone pairs.

A lone pair of electrons is slightly closer to the central atom, and occupies more space than a bonded pair, this results in a lone pair repelling more strongly than a bonded pair

Question 3

2 bp
0 lp

Answer 3

Linear
180˚

Question 4

3 bp
0 lp

Answer 4

Trigonal planar
120˚

Question 5

4 bp
o lp

Answer 5

Tetrahedral
109.5˚

Question 6

5 bp
0 lp

Answer 6

Trigonal bipyramidal
120˚ 90˚

Question 7

6 bp
0 lp

Answer 7

Octahedral
90˚

Question 8

4 bp
1lp

Answer 8

Trigonal pyramidal
107˚

Question 9

4 bp
2 lp

Answer 9

Bent / Angular
104.5˚

Question 10

6 bp
4 lp

Answer 10

Linear
180˚

Question 11

What is electronegativity?

Answer 11

The ability of an atom to attract the bonding electrons in a covalent bond

Question 12

What are the most electronegative elements?

Answer 12

NOF

Question 13

What is the electronegativity difference for covalent bonds?

Answer 13

0

Question 14

What is the electronegativity difference for polar covalent bonds?

Answer 14

0 to 1.8

Question 15

What is the electronegativity difference for ionic bonds?

Answer 15

greater that 1.8

Question 16

When will a bond be non-polar?

Answer 16

Bonded electron pair is shared equally between two bonded atoms

• bonded atoms are the same
• bonded atoms have the same or similar electronegativity

Question 17

When will a bond be polar?

Answer 17

Bonded electron pair is shared unequally between two bonded atoms

• nodes atoms are different and have different electronegativity values

Question 18

How do you generally figure out if a molecule is polar or non-polar without electronegativity values?

Answer 18

1. Draw molecule, accurate shape
2. Add dipole charges
3. Draw direction of charges (+ve to -ve)
4. If dipoles cancel; non-polar, if overall dipole; polar

Question 19

What are intermolecular forces?

Answer 19

Weak interactions between dipoles of different molecules

Question 20

What are the different types of intermolecular forces?

Answer 20

• induced dipole-dipole interactions (london forces)
• permanent dipole-dipole interactions
• hydrogen bonding

Question 21

Order the types of intermolecular forces in order of increasing strength

Answer 21

• induced dipole-dipole interactions (london forces)
• permanent dipole-dipole interactions
• hydrogen bonding

Question 22

What are Induced dipole-dipole interactions (london forces) and where do they act?

Answer 22

London forces are weak intermolecular forces that exist between all molecules.

They act between induced dipoles in different molecules

Question 23

Where do permanent dipole-dipole interacts act?

Answer 23

They act between the permanent dipoles in different polar molecules

Question 24

What is the structure of a simple molecular lattice?

Answer 24

• molecules are held in place by weak intermolecular forces
• the atoms within each molecule are bonded together strongly by covalent bonds

Question 25

What are the properties of a simple molecular lattice and why?

Answer 25

Do not conduct electricity -> no mobile charge carriers Low melting and boiling points -> weak intermolecular forces (the covalent bonds don’t break) Non-polar simple molecular substances are soluble in non-polar solvents -> intermolecular forces form, weaken simple molecular substances forces Non-polar simple molecular substances are insoluble in polar solvents -> There is little interaction between molecules Polar simple molecular substances solubility is hard to predict

Question 26

What is Hydrogen bonding?

Answer 26

Intermolecular bonding between molecules containing N, O, or F and the H atom

Question 27

What are the anomalous properties of water?

Answer 27

- Ice is less dense than water - Water has high melting and boiling points

Question 28

Why is ice less dense than water?

Answer 28

Hydrogen bonds hold water molecules apart in an open lattice structure. The water molecules in ice are further apart than in water Solid ice is less dense than liquid water and floats

Question 29

Why does water have high melting and boiling points?

Answer 29

Water has london forces and hydrogen bonds Lots of energy is required to break the hydrogen bonds