Chemistry GCSE types of structures

I got this question in a chemistry paper, and thought that substance B was graphite, because it conducts electriicty, high melting boiling point etc, however in the mark scheme it says it's metallic bonding but I was wondering how I would tell the difference only been given the info in this table?

Thanks for any help!

(edited 2 months ago)

Reply 1

TypicalNerd

Original post by lostwooloo

Thanks for any help!

Imo it’s a badly designed question, but I would agree with the MS as graphite doesn’t really melt - it sublimes at a much higher temperature (circa 3500°C iirc, assuming atmospheric pressure).

Metallic bonding on the other hand seems to be correct as the melting point is characteristically quite high (think strong attraction between the metal cations and delocalised electrons) and the conductivity is excellent in both the solid and liquid states (due to the delocalised electrons being able to carry an electrical current).

I suppose one way you could justify that graphite isn’t a possibility is that it is a giant covalent substance and so on melting you would have to break many strong covalent bonds - this would mean there would cease to be any delocalisation of electrons in the structure and it would lose its electrical conductivity when not in the solid state.

(edited 2 months ago)

Reply 2

Nitrotoluene

Original post by lostwooloo

Thanks for any help!

Hello lostwooloo!

My opinion on this is as follows:
Substance A:
Melting point: 1180°C
Conductivity: Poor in solid state, good in molten state.
Structure and bonding: For me it is an ionic compound like a salt as sodium chloride or strong hydroxide like sodium hydroxide.
High melting point = strong ionic bonds.
Poor conductivity in solid state = crystalline structure.
Good conductivity in the molten state = presence of free moving ions. Compounds that can be electrolysed in molten state.
Substance B:
Melting point: 1538°C
Conductivity: Good in both solid and molten state.
Structure and bonding:. High melting point and good conductivity in both states = metal (i.e.: chromium, nickel)
Substance C:
Melting point: 115°C
Conductivity: Poor in both solid and molten state.
Structure and bonding: For me is a molecular compound, most likely an organic compound.
Low melting point = weak intermolecular forces.
Poor conductivity in both states = ~~absence~~ lack of free moving charged particles.

Bye,
Sandro

(edited 2 months ago)