Properties of Transition Metals

Transition metals are a group of elements located in the d-block. They are placed between the main group elements and exhibit unique characteristics, such as electrical conductivity, colors, hardness, high melting points, and magnetism.

Many of these characteristics are attributed to the filling of d orbitals. Moving across the period, electrons are added following the Aufbau principle. However, the outermost s orbital is filled first, before the electron enters the (n − 1) d subshell, with some exceptions. Chromium and copper have a half-filled s orbital because it is energetically more favored to have a half-filled or full d subshell.

The atomic size of transition metals decreases slightly across a period. As the electrons enter the d subshell, the number of valence electrons in the outermost s orbital remains steady, leading to an overall constant nuclear charge. Down the column, the trend increases from the fourth to the fifth period, but not below.

The 6th period contains 14 additional elements of the lanthanide series, where electrons enter the (n − 2)f subshell before entering the (n − 1)d subshell. Electrons located in the f orbitals do not sufficiently shield the valence electrons in the outermost s orbital, resulting in an increased effective nuclear charge. Thus, the valence electrons are attracted more strongly, leading to smaller than expected atomic radii. This is known as the Lanthanide contraction.

Similarly, the transition elements’ electronegativity is influenced by its atomic size and nuclear charge. Moving across a period, it increases only slightly. Down the column, the electronegativity increases from the fourth to the fifth period but remains constant in the sixth period. This is attributed to a decrease in atomic size and an increase in the nuclear charge.

The ionization energy of transition metals increases slightly across a period. Interestingly, down the column, it is higher for the 6th period than the 4th and 5th periods. Here, the valence electrons are held more tightly as the nuclear charge increases with a negligible increase in atomic size.

Lastly, transition metals can have a range of stable oxidation states by losing outermost s orbital electrons before the unpaired d orbital electrons. The partially filled d orbitals enable oxidation states ranging from +7 to +1, characteristic colors, and magnetic properties.