2021 H2 Chem P1 Q30 — Transition elements Solution

The answer is D (both 1 and 2).

Property 1 (melting point 3180 °C) is typical of a transition element. A typical s-block metal has weak metallic bonding, because only 1 or 2 electrons per atom are delocalised and the cations are large, so it has a relatively low melting point (calcium melts at 842 °C). In a transition element both the 4s and 3d (here 6s and 5d) electrons can be delocalised and the cations are smaller, so the metallic bonding is much stronger and the melting point is high.

Property 2 (density 21 020 kg m\(^{-3}\) = 21.0 g cm\(^{-3}\)) is typical of a transition element. s-block metals have relatively low relative atomic mass and large metallic radius, so they have low densities (calcium 1.55 g cm\(^{-3}\)). Transition elements have higher relative atomic mass and smaller metallic radius, so they are much denser (typically above 5 g cm\(^{-3}\)).

• A is wrong: both properties are typical of a transition element, not neither.
• B is wrong: it leaves out property 2; the high density is also typical of a transition element.
• C is wrong: it leaves out property 1; the high melting point is also typical of a transition element.