Shapes of molecules and ions (6)

Question 1

Electron repulsion

Answer 1

When you have a pair of electrons they will repel each other, but will also repel other electron pairs in the molecule so the bonded pairs will position themselves as far apart as possible which gives the molecule a specific shape

Question 2

Which repels more, bonded or lone pairs?

Answer 2

Lone pairs will repel a lot more than a bonded pair so they will push the bonded pairs further apart from it and they will be moved closer together

Question 3

Tetrahedral

Answer 3

4 bonded pairs, 0 lone pairs

109.5 angle

Question 4

Trigonal planar

Answer 4

3 bonded pairs 0 lone pairs

120 angle

Question 5

Linear

Answer 5

2 bonded pairs, 0 lone pairs

180 angle

Question 6

Pyramidal

Answer 6

3 bonded pairs, 1 lone pair

107 angle

Question 7

Non-Linear

Answer 7

2 bonded pairs, 2 lone pairs

104.5 angle

Question 8

Trigonal Bipyramidal

Answer 8

5 bonded pairs, 0 lone pairs

120 and 90 angles

Question 9

Octahedral

Answer 9

6 bonded pairs, 0 lone pairs

90 angle

Question 10

T-shaped

Answer 10

3 bonded pairs, 2 lone

<90 angle

Question 11

Umbrella

Answer 11

5 bonded pair, 1 lone pair

90, <90 angle

Question 12

What is electronegativity?

Answer 12

The ability of an nuclei of an atom in a covalent bond to attract the shared pair of electrons

Question 13

What affects the electronegativity of an atom?

Answer 13

How big the nuclear charge is and how big the atomic radius is

Question 14

How is electronegativity measured?

Answer 14

The Pauling Scale

Question 15

What are the most electronegative elements?

Answer 15

Fluorine, nitrogen, oxygen and chlorine

Question 16

How do you know if it’s an ionic or covalent bond using the Pauling scale?

Answer 16

If it’s 0 its a pure covalent which means atoms of the same element are bonded together.
If it’s 0-1.8 its a polar covalent which means the shared pair of electrons are closer to one atom than the other
If it’s more than 1.8 it’s ionic because the shared pair of electrons is a lot closer to one of the atoms than the other until they become accepted by it to form ions.

Question 17

When will a bond be non-polar?

Answer 17

When the two atoms in a covalent bond are the same or have very similar electronegativities

Question 18

When will a bond be polar?

Answer 18

When both of the atoms have different electronegativity values which means the electronegative atom will have a stronger attraction to the shared pair of electrons and so will create a partially positive and negative dipole.

Question 19

Is water a polar molecule, why?

Answer 19

Water is a polar molecule because O-H is a polar bond. The oxygen is far more electronegative than hydrogen so attracts the pair of electrons and becomes partially negative while hydrogen becomes partially positive. Because water is a non-linear molecule, the two polar bonds don’t cancel.

Question 20

Is CO2 a polar molecule, why?

Answer 20

CO2 is not a polar molecule. This is because even though C=O is polar, the molecule is linear so the dipoles act in opposite directions and get cancelled out.

Question 21

Why are ionic lattices soluble in polar solvents?

Answer 21

Because the partial charges on the dipole can attract the ions in the lattice and break it apart. E.g NaCl will dissolve in water because the partially positive H will attract the Cl- and the partially negative O will attract the Na+

Question 22

What is an intermolecular force?

Answer 22

Weak interactions between dipoles of different molecules. These could be London forces, permanent dipole-dipole interactions and hydrogen bonding

Question 23

What are London forces?

Answer 23

They are induced dipole-dipole interactions and weak intermolecular forces that occur between all molecules

Question 24

How are London forces created?

Answer 24

Electrons are constantly moving around so instantaneous dipoles are being created in molecules. This then triggers instantaneous dipoles in other molecules and they attract each other. In the next instant, the dipole may disappear.

Question 25

How strong are London forces?

Answer 25

The more electrons there are in the molecules that are interacting, the more instantaneous dipoles are formed, the more induced dipole and the stronger the intermolecular forces will be. They are very easily broken however so don’t have a high boiling point compared to any other bond.

Question 26

What are van der Waals forces?

Answer 26

Something that describes both induced and permanent dipole-dipole interactions. This isn’t used anymore as we have refined it.

Question 27

Permanent dipole-dipole interactions

Answer 27

The intermolecular forces between a partially positive dipole on one molecule and a partially negative dipole on another molecule.

Question 28

What is a simple molecular substance?

Answer 28

A substance made up of simple molecules with small numbers of atoms like H2O and CO2

Question 29

What do simple molecular substances look like in solid state?

Answer 29

They exist as simple molecular lattices which have weak intermolecular forces between molecules that can be broken easily and strong forces between the atoms in the molecules.

Question 30

What is the melting and boiling point of a simple molecular substance?

Answer 30

It has a low melting and boiling point because it doesn’t take a lot of energy to overcome the weak intermolecular forces.

Question 31

What happens when a simple molecular substance is added to a non-polar solvent?

Answer 31

If the simple molecular substance is non-polar, it will dissolve in the non-polar solvent because there will be intermolecular forces formed between the solvent and substance which will weaken the intermolecular forces in holding the lattice together, so the simple molecular substance will dissolve. If the simple molecular substance is polar, it will not interact with the solvent so won’t dissolve in it

Question 32

What happens when a simple molecular substance is added to a polar solvent?

Answer 32

It will only dissolve in the solvent if it is polar as the solute and solvent molecules attract each other so the intermolecular forces will break. The solubility always depends on how strong the dipole is.

Question 33

Can simple molecular solvents carry electricity?

Answer 33

No, because there are no mobile charges that can move around to conduct electricity.

Question 34

What is hydrogen bonding?

Answer 34

A hydrogen bond is an electrostatic attraction between partially negative oxygen on one molecule and partially positive hydrogen on another molecule. They are the strongest type of intermolecular force.

Question 35

What are some anomalous properties of water?

Answer 35

• Ice is less dense than water

- Water has a very high specific heat capacity

Question 36

Why is ice less dense than water?

Answer 36

Because when water freezes, the water molecule forms 4 hydrogen bonds and the molecules extend outwards and further apart which creates large tetrahedral holes in the structure. This makes ice a lot less dense than water so it can float on top.

Question 37

Why does water have such high specific heat capacity?

Answer 37

Because it has hydrogen bonds between the water molecules which require energy to break and water also have London forces between them which requires additional energy to overcome.