1.5 Solid Structures

Question 1

Describe the properties of giant ionic lattices

Answer 1

• high M+B point due to strong forces of attraction between ions
• conduct when molten/dissolved as ions can move and carry a charge
• dissolve in polar solvent as have 2 opposite charges so the solvent infiltrates and breaks the lattice apart

Question 2

Shape + coord number of NaCl

Answer 2

6:6
Cubic

Question 3

Shape and coord number of CsCl

Answer 3

8:8
Body centred cubic

Question 4

Describe the properties of simple molecular structures

Answer 4

• weak VdW forces and strong covalent bonds between atoms
• low M+B points: weak attraction and weak VdW
• do not conduct: no delocalised electrons
• soluble in non-polar solvents: same intermolecular forces so essentially intertwine as VdW interact
  —> 114BP is iodine

Question 5

Describe the properties of giant covalent structures

Answer 5

• high M+B point: strong covalent bonds between atoms
• don’t conduct (expect graphite): no free delocalised electrons
• insoluble in polar and non-polar solvents: don’t interact as no VdW
• very hard (except graphite): only covalent bonds present
  —> graphite soft as layers able to slide due to VdW

Question 6

Describe metallic bonding

Answer 6

• force of attraction between a positive ion and a delocalised electron
  —> bonding within a metal atom

Question 7

Describe properties of metallic bonding

Answer 7

• high M+B point: strong metallic bonds
• conduct electricity: all have delocalised electrons
  —> more outer electrons = better conductor
• malleable and ductile: able to bend as delocalised electrons move to form new metallic bonds

Question 8

Explain why iodine can be converted to a gas at a much lower temp than diamond

Answer 8

• Van der Waals need to be broken betwene molecules to make iodine gas
• covalent bonds need to be broken between molecules to make gas form diamond
• VdW much weaker than covalent

Question 9

Why is MP of Na lower than that of Mg

Answer 9

• both metallic bonds
• more energy to break in Mg as 2 electrons involved in delocalisation

Question 10

Why is chlorine a gas but iodine is solid at room temp and pressure?

Answer 10

• van der waals strong in iodine than chorine as iodine has more electrons and therefore more energy is needed to overcome the forces, so there’s a higher boiling point

Question 11

Why does sodium have a lower melting temp than aluminium?

Answer 11

Aluminium has more valence electrons than sodium and therefore stronger metallic bonds

Question 12

Why does silicon have a higher melting temp than phosphorus?

Answer 12

Silicon has giant molecular structure whereas phosphorous only has weak forces between molecules

Question 13

Why is the melting temp of sodium iodide lower than that of sodium chloride?

Answer 13

Iodine ion is larger than chlorine so there’s less attraction to the sodium ion

Question 14

Why is the boiling temp of iodine mono chloride higher than chlorine?

Answer 14

ICl is larger than Cl2 so there’s more electrons and therefore greater VdW between molecules