Unit 1.5 - Solid Structures

Question 1

How are ions held together in an ionic lattice?

Answer 1

Strong electrostatic forces of attraction between oppositely charged ions are greater than the electrostatic repulsion between ions with the same charge.

Question 2

What 2 factors determine the way a crystal is formed (ions in a lattice are arranged)?

Answer 2

Ratio of cations to anions and relative relationship between the sizes of ions involved (radius ratio).

Question 3

1) What is the coordination number of sodium chloride?

2) What does this mean?

Answer 3

1) 6:6

2) Each Na+ ion is surrounded by six Cl- ions and vice versa.

Question 4

1) What is the coordination number of caesium chloride?

2) What does this mean?

Answer 4

1) 8:8

2) Each Cs+ ion is surrounded by 8 Cl- ions and vice versa.

Question 5

Coordination number

Answer 5

Tells you the number of oppositely charged ions which surround that particular ion.

Question 6

1) Why are ionic substances said to be involatile?

2) State another property of ionic compounds.

Answer 6

1) High melting points - large amount of energy to break electrostatic attractions between oppositely charged ions
2) Hard but brittle - layers of ions slide over each other causing ions same charge to be next to each other, ions repel and crystal shatters.

Question 7

Involatile

Answer 7

Not easy to melt or boil.

Question 8

Why are ionic crystals hard to cut?

Answer 8

Displace one layer of ions relative to the next. As a result of displacement, ions of similar charge come close together and repel each other forcing apart the two portions of the crystal.

Question 9

1) Explain whether solid ionic substances conduct electricity.
2) Explain whether molten ionic substances conduct electricity.

Answer 9

1) Don’t - Ions fixed in position by ionic lattice held by ionic bonds and aren’t free to carry electric charge.
2) Molten/dissolved in water conduct electricity as are free to move to electrode and carry electric charge.

Question 10

Allotropes

Answer 10

Different forms of the same element in the same state e.g. allotropes of carbon are diamond and graphite.

Question 11

1) Describe the bonding in diamond.

2) State 2 properties.

Answer 11

1) Every carbon atoms forms 4 strong single covalent bonds to 4 other carbon atoms in a tetrahedral arrangement.
2) High melting temperature (sublimes, solid to gas -at 3500) and hard due to strength of covalent bonds.

Question 12

State 4 properties of macromolecular (giant covalent) structures.

Answer 12

1) Hard
2) Involatile
3) Insoluble
4) Non-conductor - no free (delocalised) electrons to conduct electricity.

Question 13

Delocalised

Answer 13

Electron isn’t attached to a particular atom, so can move between atoms.

Question 14

1) Describe the bonding in graphite.

2) What causes graphite to act as a lubricant?

Answer 14

1) Each carbon is covalently bonded to 3 other carbon atoms in a planar, hexagonal arrangement. 4th electron is delocalised within the layer.
2) Weak Van der Waals’ forces exist between layers, easily broken, layers can slide over each other.

Question 15

1) Why is graphite an electrical conductor?

2) Why does it have a higher melting point than diamond?

Answer 15

1) Pane of layers - one valence electron is left in orbital and so they delocalise over plane and are free to move.
2) C-C bonds are shorter and stronger.

Question 16

1) What is iodine made up of?
2) What forces are present in-between the layers?
3) What bond holds the two iodine molecules together?

Answer 16

1) Symmetrical, non-polar molecules.
2) Van der Waals’ forces/induced dipole-induced dipole interactions.
3) Covalent bonds.

Question 17

Why does solid iodine have a low melting/boiling point?

Answer 17

Van der Waals’ forces are weak, covalent bonds aren’t relevant as aren’t broken. Remains molecules as a solid, liquid and gas.

Question 18

1) What property does ice have?

2) What bonds does ice contain?

Answer 18

1) Ice is less dense than water.

2) Arranged in rings of 6 held by hydrogen bonds.

Question 19

1) Describe the volatility of simple molecular substances.
2) Describe the conductivity.
3) Describe the solubility.

Answer 19

1) Soft with low melting/boiling points.
2) Don’t conduct when molten or dissolved in water - no free moving electrons or ions in physical state.
3) Non polar are insoluble in polar solvents (water) and soluble in non-polar solvents (hexane) as can’t form dipole-dipole interactions or hydrogen bonds with water.

Question 20

Valence electrons

Answer 20

Outer shell electrons

Question 21

Using the ‘sea of electrons model’, explain why metals are good thermal and electrical conductors.

Answer 21

Electrons free to flow and carry charge, kinetic energy transferred form hotter part to cooler part because of the vibrations of the cations and free moving electrons.

Question 22

Why is aluminium more conductive than sodium?

Answer 22

Al more conductive than Na because 3 electrons are released into the sea rather than 1.

Question 23

Why are metals malleable and ductile?

Answer 23

When force is applied to a metal the layers of cations can slide over each other. However, the delocalised electrons move with the cations and prevent forces of repulsion forming between the layers.

Question 24

What is the relationship between volatility and hardness in metals?

Answer 24

Stronger bonding, higher melting point and stronger the metal.

Question 25

1) What happens to the metabolic bond strength and melting points of metals as you go down the group?
2) What happens to the cations?

Answer 25

1) Strength and meting points decrease.
2) Cations become larger so charge density becomes less. Larger cations are less attracted to lattice so metabolic bonding is weaker.

Question 26

Explain why there is a large difference in the volatility of Li and Cs.

Answer 26

Both group 1 - metallic bond strength of Cs is lower than Li due to increase in Cs cation. Therefore, there is a reduction in the charge-size ratio.

Question 27

Explain why there is a large difference in the volatility of Na and Al.

Answer 27

Both period 3 - similar size, Na = Na+, Al = Al 3+ - higher number of delocalised electrons resulting in a stronger metallic bond.