Why does lead have a lower melting point than most other metals?

Answer 1

Unlike metals, pure elemental non-metals do not have the ability to share electron orbitals as easily. This means non-metals tend to have poor bond strength across the entire material. Because of these weak bonds, non-metals tend to be flaky and powder as well as brittle. This trend of weak bonds isn't entirely true for all non-metals; diamonds, an allotrope of carbon, have incredibly strong bonds and crystal structure. A substance's melting point is largely dependent on how much energy is necessary to tear a substance's atoms from their positions relative to their neighboring atoms. As sulfur is a non-metal it exhibits these properties and this is why its melting point is rather low compared to other substances, particularly metals.

Answer 2

Lead is not actually an exception to the trend of melting points in metals. As you go down the groups, the mpt of the metals decrease because there is more shielding around the nucleus and the electrons are not as attracted [to the nucleus]. Although the nuclear charge is greater in, for example Thallium than in aluminium, the increase in shielding in thallium overcomes the greater nuclear charge causing the metallic bonds are weaker and require less energy to break.

This trend is observed in every group of metals.