Deducing structure from the evidence

By the end of this lesson

By the end you can deduce a substance's structure and bonding from data such as melting point, conductivity and solubility.

The evidence table

Data questions hand you properties and ask for the structure. Here is how to read each clue:

clue	points to	because
high melting point, does not conduct as solid, conducts when molten or aqueous	giant ionic	ions locked in lattice; free when molten/dissolved
low melting point, does not conduct in any state	simple molecular	weak forces between molecules; no mobile charges
very high melting point, does not conduct (except graphite)	giant molecular	covalent network; electrons locked in bonds
very high melting point, conducts as a solid	graphite (giant molecular)	delocalised electrons within layers
high melting point, conducts as a solid, malleable	giant metallic	delocalised electrons; sliding layers
dissolves in water, not in a non-polar solvent	ionic	polar water can attract the ions
dissolves in a non-polar solvent, not in water	simple molecular (non-polar)	like dissolves like

Definition

Deduction template

Three sentences that always work:

"The data shows [clue]."
"This is typical of a [structure], because [reason from the table]."
"So the bonding is [ionic / covalent / metallic / intermolecular]."

Worked example: Substance A

Substance A melts at $801\ ^\circ\text{C}$ . It does not conduct electricity as a solid, but it does conduct when molten and when dissolved in water. Deduce its structure and bonding.

Have a go first?

Worked example: Substance B

Substance B melts at $114\ ^\circ\text{C}$ , does not conduct electricity in any state, and dissolves in hexane but not in water. Deduce its structure and bonding.

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Your turn

Multiple choiceQuestion 1 · Apply

Short answerQuestion 2 · Stretch

Multiple choiceQuestion 3 · Recall

Answer the 3 questions above to continue.