MDCAT Chemistry · Chemistry · Transition elements. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
The d-block elements lie between the s and p blocks. A transition element has a partly filled d subshell in its atom or in one of its common ions. In the 3d series the 4s orbital fills before 3d, but when ions form the 4s electrons are lost first.
The 3d and 4s electrons are very close in energy, so different numbers of them can be used in bonding. This gives variable oxidation states.
Most special properties come from the partly filled d subshell. Unpaired d electrons make the substances paramagnetic. Electrons moving between d orbitals give colour. The ability to change oxidation state, and to hold molecules on the metal surface, makes good catalysts.
Students remove 3d electrons first when writing an ion. The 4s electrons always go first: Fe is [Ar] 3d6 4s2, so Fe2+ is [Ar] 3d6, not [Ar] 3d4 4s2.
Answer: Three unpaired electrons, so Co2+ is paramagnetic (and coloured).
Type what you are stuck on. The helper finds the explanation, worked examples and the notes to read, free and instant.