S-Cool Revision Summary

S-Cool Revision Summary

Definition: An element that has its 'd' orbitals partly filled, in some of its compounds.

They are hard, lustrous, weakly electropositive metals with high melting and boiling points.

The high melting points are due to the 3d and 4s electrons being available for delocalisation, hence the large electrostatic attraction.

Density increases across period as nuclear charge increases.

The 3d orbital has a higher energy than the 4s - hence electrons fill the 4s before the 3d.

On ionisation, the 4s empties before the 3d due to repulsion between 3d and 4s electrons. Therefore, the 4s are pushed to a higher energy level than 3d.

They have variable oxidation states due to the ability to lose electrons from 4s and 3d relatively easily.

The increase in stability of +2 oxidation state is explained by the greater difficulty of removing a third electron as the nuclear charge increases. However, Fe3+ is more stable than Fe2+ due to stability of 3d5 arrangement.

They form coloured compounds. Compounds that are coloured have electrons promoted from a ground state to an excited state. This is made possible due to the splitting of the d-orbitals into respective higher and lower energy levels. When the excited electron 'drops' back to a ground state a photon of light energy is released.

They form complexes - a complex is formed when a central metal atom or ion is surrounded by species that donate lone pairs of electrons.

A ligand is a species that donates a lone pair of electrons to a central metal atom or ion. The ligands make co-ordinate (or dative) bonds with the central atom/ion.

Ligand exchange may occur if the complex ion produced is more stable.

The addition of aqueous solutions of sodium hydroxide or ammonia may cause the production of coloured hydroxide precipitates. Some of these precipitates dissolve in excess alkali, while others dissolve in ammonia.