22.1: Periodic Trends in the Transition Elements

Transition Elements:



Transition Elements: those metallic elements that have an incompletely filled d subshell or easily give rise to common ions that have incompletely filled d subshells. Highlighted in the table above. They are the basis for Inorganic Chemistry (every other element except carbon).

Periodic Trends of the Transition Elements:

1. They are all metals.

2. Mostly have high melting points and high boiling points and are hard solids. This is due to metallic bonding.



The negatively charged electrons form an “electron sea” around the positively charged nuclei of the metal atoms and are shared as they move about the sea.

3. They have more than one oxidation state (exceptions: Cd²⁺, Ag⁺, Zn²⁺).

Example:

Fe²⁺, Fe³⁺; Mn²⁺, Mn³⁺, Mn⁴⁺, Mn⁷⁺.

4. Transition metal ion solutions have a color.




Atomic Radii:

For the main group elements, covalent radii decrease in size across a row due to effective nuclear charge: the positive pull of the nucleus on the negative electrons. This is the positive nuclear charge that acts on the covalent electrons to pull them in, diminished (shielded) by any electrons between them.



Going down from the fourth period to the fifth period, the atomic radii increase. Further down to the sixth period, atomic radii are approximately the same as they are in the fifth period.

This similarity is due to lanthanide contraction. The lanthanides are the first row of the inner transition elements (placed at the bottom of the table), from cerium to lutetium. Here, the 4f subshell is filled, and by the time we get back to this row of transition elements with hafnium, the covalent radius is practically the same as the elements in the row above it.