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Bonding and Structure

Topic 6 of 6

Work backwards from the evidence

Use melting point and conductivity together to identify and explain a likely structure.

O-Level 2026 SEC G3 2027. Extensions are labelled Pure only.

Work backwards from the evidence

Use several properties together, then explain the particles, attractions and charge carriers.

Worked example

Identify a likely structure

An unknown solid melts at a high temperature. It does not conduct when solid, but conducts after melting. What structure is most likely?

  1. The high melting point suggests strong attractions extending through the solid.
  2. The molten material has mobile charged particles.
  3. The solid lacks mobile charge carriers. That makes a metal unlikely.
  4. An ionic lattice fits both observations: fixed ions in the solid, mobile ions after melting.
Answer

A giant ionic structure. Strong electrostatic attractions require much energy to overcome; ions carry charge only when free to move.

Pure only

Worked example

Predict a compound from electron arrangement

Element X has electron arrangement 2,8,2. Predict its bonding and formula when it reacts with chlorine.

  1. X can lose two outer electrons to form X2+, with a full outer shell.
  2. Each chlorine atom gains one electron to form Cl-.
  3. Two chloride ions balance one X2+ ion.
Answer

XCl2, with ionic bonding between X2+ and Cl-. The electron arrangement helps predict chemical behaviour as well as physical properties.

Check your understandingA pure substance melts at a low temperature and does not conduct as a solid or liquid. Suggest a structure and explain the low melting point.Think it through, then reveal the answer
A simple molecular structure is likely. Relatively little energy is needed to overcome weak intermolecular forces. The covalent bonds within the molecules remain intact during melting.