Melting points of two substances, A and B, and the abilities of the substances to conduct an electric current when solid and when molten. One of the substances has an ionic structure and one has a simple molecular, covalent structure. Explain, in terms of bonding and the forces between the particles, the relative melting points and abilities to conduct the electric current of substances A and B – 9010.

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1. Substance A has a simple molecular (covalent) structure:

   Composed of separate molecules held together by weak intermolecular forces (London dispersion, possibly dipole–dipole).

   This gives low melting point because little energy is needed to overcome these weak forces.

   It does not conduct electricity in solid or molten state—no free electrons or ions.

   Substance B has an ionic structure:

   Made of a giant lattice of positively and negatively charged ions held by strong electrostatic attractions.

   It has a high melting point because a lot of energy is needed to break these strong ionic bonds.

   Electrical conductivity:

   Solid: ions are fixed → does not conduct.

   Molten: ions become mobile → conducts electricity.

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