Chapter 6

Question 1

What is the electron-pair repulsion theory?

Answer 1

Electron pairs around a central atom determine the shape of the molecule/ion.

Electron pairs repel to be as far apart as possible, the arrangement therefore minimises repulsion.

Question 2

What does the solid line show?

Answer 2

A bond in the plane of the paper

Question 3

What does the solid wedge show?

Answer 3

A bond that comes out of the plane of the paper

Question 4

What does the dotted wedge show?

Answer 4

A bond that goes into the plane of the paper

Question 5

Why do lone pairs repel more strongly then bonded pairs?

Answer 5

A lone pair of electrons is slightly closes to the central atom and occupies more space.

Question 6

By how much does a lone pair reduce a bond angle?

Answer 6

2.5 degrees

Question 7

What is a tetrahedral shape like?

Answer 7

4 bonded pairs, 0 lone pairs

2 solid lines next to each other, 1 dotted wedge and one solid wedge.

109.5 degrees

Question 8

What is a pyramidal shape like?

Answer 8

3 bonded pairs, 1 lone pair

1 of each, solid/dashed/line

107 degrees

Question 9

What is a non-linear shape like?

Answer 9

2 bonded pairs, 2 lone pairs.

1 straight line and one solid wedge.

104.5 degrees

Question 10

What is a linear shape like?

Answer 10

2 electron pairs, O lone pairs

2 double bonds

180 degrees

Question 11

What is a trigonal planar shape like?

Answer 11

3 electron pairs, 0 lone pairs

3 straight lines

120 degrees

Question 12

What is an octahedral shape like?

Answer 12

6 electron pairs, 0 lone pairs.

2 of each type of line/wedge. the solid wedges at bottom left and right, dotted at top left and right, straight lines at top and bottom.

90 degrees

Question 13

What is electronegativity?

Answer 13

The attraction of a bonded atom for the pair of electrons in a covalent bond.

The shared pair of electrons may experience more attraction from one of the bonded atoms than the other.

Question 14

How is electronegativity measured?

Answer 14

The Pauling scale is used.

Question 15

In which direction does the electronegativity values increase?

Answer 15

Across and up (the most electronegative is Florine)

Question 16

What is the bond type if the electronegativity difference is 0?

Answer 16

Covalent

Question 17

What is the bond type if the electronegativity difference is 0-1.8?

Answer 17

Polar covalent

Question 18

What is the bond type if the electronegativity difference is greater then 1.8?

Answer 18

ionic

Question 19

How is the bonded electron pair shared in a non-polar bond?

Answer 19

Its shared equally between the bonded atoms.

This normally occur when the bonded atoms are the same eg H-H

Question 20

How is the bonded electron pair shared in a polar bond?

Answer 20

Its shared unequally between the bonded atoms.

Polar bonds occur when there is a difference in electronegativity values between atoms.

Question 21

Is the more electronegative atom going to have a delta positive or negative charge?

Answer 21

Delta negative

Question 22

What is a dipole?

Answer 22

The separation of two opposite charges

Question 23

What is a permanent dipole?

Answer 23

A dipole in a polar covalent bond that doesn’t change.

Question 24

How is a molecule polar when there is electronegativity difference?

Answer 24

H2O is polar. Both of the O-H bonds have a permanent dipole and act in different directions, they dont oppose each other so the dipoles dont cancel out.

Question 25

How is a molecule non-polar when there is electronegativity difference?

Answer 25

CO2 is non-polar. Despite them each having a permanent dipole, they act in opposite directions so the dipoles cancel C=O

Question 26

What are intermolecular forces?

Answer 26

Weak interactions between dipole of different molecules.

Question 27

What are the 3 types of intermolecular forces?

Answer 27

-London forces (induced dipole-dipole interactions) -permanent dipole-dipole interactions -hydrogen bonding

Question 28

What are intermolecular forces responsible for?

Answer 28

physical properties like melting/boiling points.

Question 29

What are London forces?

Answer 29

Weak intermolecular forces between all molecules, the movement of electrons produces a changing dipole in a molecule. At any instant an instantaneous dipole will exist and this induces a dipole on a neighbouring molecule which then induces further dipoles on neighbouring molecules. So they all attract one another.

Question 30

How does a molecule having more electrons impact its London forces?

Answer 30

- larger the instantaneous and induced dipoles - greater the induced dipole-dipole interactions - Stronger attractive forces between molecules so they have larger boiling points since more energy is needed to overcome the intermolecular forces.

Question 31

What is a simple molecular substance?

Answer 31

Made up of simple molecules (small units with a definite number of atoms with a definite molecular formula).

Question 32

What is the structure of a simple molecular substance?

Answer 32

Simple molecular lattice. They are held in place by weak intermolecular forces. But the atoms in the molecules are bonded together strongly by covalent bonds.

Question 33

Describe the melting/boiling point of a simple molecular substance?

Answer 33

Weak intermolecular forces are broken with not much energy, they are weak. So simple molecular substances have low mp/bp. But only the weak intermolecular forces holding the lattice together break, not the strong covalent bonds between atoms.

Question 34

Describe the solubility of a simple molecular substance? (NON-POLAR ADDED TO POLAR)

Answer 34

When a non-polar simple molecular substance is added to a polar solvent there is little interaction between the molecules in the lattice and the solvent molecules. So the intermolecular bonding in the polar solvent is too strong to be broken. So non-polar simple molecular substances are insoluble in polar solvents.

Question 35

Describe the solubility of a simple molecular substance? (NON-POLAR ADDED TO NON-POLAR)

Answer 35

When a simple molecular compound is added to a non-polar solvent intermolecular forces form between them. The interactions weaken the intermolecular forces in the simple molecular lattice so they break and the compound dissolves. So non-polar simple molecular substances are soluble in non polar substances.

Question 36

Describe the solubility of a simple molecular substance? (Polar added to polar)

Answer 36

The polar molecules attract each other so they dissolve. The solubility depends on the strength of the dipole.

Question 37

Describe the electrical conductivity of a simple molecular substance?

Answer 37

There are no mobile charged particles in simple molecular structures so there is nothing to complete an electrical circuit. Therefore simple molecular structures are non-conductors of electricity.

Question 38

What is a hydrogen bond?

Answer 38

Permanent dipole-dipole integration between molecules with an electronegative atom with a lone pair of electrons or a hydrogen atom. It acts between a lone pair of electrons on an electronegative atom in one molecule and a hydrogen atom in a different molecule