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.

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.