Transition Metals - The Basics

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Transition Metals are Found in the d-Block

The b-block is the block of elements in the middle of the periodic table. Most of the elements in the d-block are transition metals (or transition elements).

You need to know about the ones in the first row, Titanium to Copper.

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Transition Metals have Partially Filled d Sub-levels in their Atoms or Ions

A transition metal is a metal that can form one or more stable ions with a partially filled d sub-level.

A d-orbital can contain up to 10 electrons. So transition metals must form at least one ion that has between 1 and 9 electrons in the d-orbital. All the period 4 d-block elements are transition metals except from Scandium and Zinc.

Ti - [Ar] 3d2 4s2

V - [Ar] 3d3 4s2

Cr - [Ar] 3d5 4s1

Mn - [Ar] 3d5 4s2

Fe - [Ar] 3d6 4s2

Co - [Ar] 3d7 4s2

Ni - [Ar] 3d8 4s2

Cu - [Ar] 3d10 4s1

It's the incomplete d sub-level that causes the special chemical properties of the transition metals.

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Sc and Zn Aren't Transition Metals

Scandium only forms one ion, Sc3+, which has an empty d sub-level. Scandium has the electron configuration [Ar] 3d1 4s2, so when it loses three electrons to from Sc3+, it ends up with the electron configuration [Ar].

Zinc only forms one ion, Zn2+, which has a full d sub-level. Zinc has the electron configuration [Ar] 3d10 4s2, so when it loses 2 electrons to form Zn2+, these are lost from the 4s sub-level, this means it keeps its full 3d sub-level.

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When Ions are Formed, the s Electrons are Removed First

Transition metals form positive ions. When this happens, the s electrons are removed first, then the d electrons.

EXAMPLE

Iron forms both Fe2+ and Fe3+ ions. What are the electron configurations of these ions?

When Iron forms 2+ ions, it loses both its 4s electrons. Fe = [Ar] 3d6 4s2 ------> Fe2+ = [Ar] 3d6

Only once the 4s electrons have been removed can a 3d electron be removed. Fe2+ = [Ar] 3d6 ------> Fe3+ = [Ar] 3d5

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The Transition Metals All Have Similar Physical Properties

The transition elements don't gradually change across the period table like you might expect.

They're all typical metals and have similar physical properties:

They all have a high density.

They all have high melting and high boiling points.

Their ionic radii are more or less the same.

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Transition Metals Have Special Chemical Properties

They can forms complex ions, e.g. Iron forms a complex ion with water - [Fe(H20)6]2+.

They form coloured ions, e.g. Fe2+ ions are pale green and Fe3+ ions are yellow.

They're good catalysts, e.g. Iron is the catalyst used in the Haber process.

They can exist in variable oxidation states, e.g. Iron can exist in the +2 oxidation state as Fe2+ and in the +3 oxidation state as Fe3+.

The coloured ions and oxidation states are shown below.

These elements show variable oxidation states because the energy levels of the 4s and 3d sub-levels are very close to one another. So different number of electron can be gained or lost using fairly similar amounts of energy.