Chemguide: Support for CIE A level Chemistry

This statement asks you to compare the melting point and density of a typical transition metal with a non-transition metal like calcium.

Before you go on, you should find and read the statement in your copy of the syllabus.

The syllabus quotes calcium for comparison purposes because it is immediately before the first transition series in the Periodic Table.

The syllabus actually compares calcium with the transition metals, but there are several cases where it is easier to compare it with the whole of the first row of d-block elements - especially for explanations.

Remember that the d-block elements include everything from scandium to zinc, but scandium and zinc themselves don't count as transition elements. (In fact the modern IUPAC definition of a transition element would include scandium, but that isn't what the CIE syllabus is using.)

Melting point

Calcium's melting point is variously quoted as 839°C or 842°C. All of the transition metals following it in the Periodic Table have higher melting points (apart from zinc, which doesn't count as a transition metal).

This is because one of the factors which control melting point is the number of electrons which are involved in the metallic bond. In calcium, only the 4s electrons are involved. With scandium and the transition metals, 3d electrons are involved as well. Zinc's 3d electrons aren't involved because the 3d level is then full.

Density

Calcium's density is quite low at 1.54 g cm^-3. The transition elements have higher densities than calcium.

Iron is fairly typical with a density of 7.89 g cm^-3.

There are two reasons for this:

As you go across the period, the atoms get heavier. The relative atomic mass of calcium is 40, but the RAM of iron is 56, for example.

Iron atoms are significantly smaller than calcium atoms. The radius of a calcium atom is 0.197 nm; the radius of an iron atom is only 0.126 nm.

That means that you can fit a lot more iron atoms into a given volume than calcium atoms. And those atoms are heavier as well. So the density is greater.

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