Question

Why are d and f block elements called transition elements?

Answer 1

They lie between the `s`-block (metals with low electronegativity) and the `p`-block (non-metals with high electronegativity) - representing the transition between the two.

They typically are considered to be the titanium family through the copper family.

Explanation:

Transition metals typically have a medium electronegativity, and as such a unique set of behaviours that vary from the `s`-block metals.

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For example, gold and some of the other "noble metals" are highly resistant to corrosion and tend to remain in their elemental state rather than becoming oxidized, but the `s`-block metals often favor the oxidized state (like sodium for example).

[This is due to the high electronegativity values (gold is `2.4`), whereas `s`-block metals would have values ranging from just below, to just above `1.0`).]

Not all transition metals exhibit this property, but as electronegativity increases during the transition from metal to non-metal, the properties & behaviours begin to vary.

From an electronic point of view, the transition metal have valence electrons that include their `ns` electrons, while additional electrons are available in the partially-occupied `(n-1)d` orbitals. From left to right, the `d` electrons become less and less available for bonding.