Variation in Atomic and Ionic Sizes of Transition Metals

The d-block of the periodic table lies from group-3 to group-12. d-block elements are also known transition elements. We define a transition element as one which contains incompletely filled d- orbitals in its ground state or any oxidation state.

We need to measure its radius, and the radius of an atom or ion can only be found by measuring the distance between two very close atoms and then halving that distance. Ionic size is also determined by this method.

Atomic Size of the Transition Metals

The atomic size is discovered with the help of the radius of the transition elements that are intermediate between those of s- and p-block elements.

The atomic radii of elements of a particular series decrease with an increase in atomic number, but this decrease in atomic radii becomes small after midway. For example, for the elements of the first transition series, the atomic radii decrease gradually from scandium to chromium, but from chromium to copper, it remains practically constant.

Ionic Size of the Transition Metals

The ionic size is calculated with the help of the ionic radius, and the ionic radius follows the same trend as the atomic radii. Since the metals exhibit different oxidation states, the radii of ions also differ. In general, the ionic size decreases with an increase in oxidation state. The ionic size generally decreases with an increase in the nuclear charge for the same oxidation state. For example, in the first transition series, the radii of bivalent metal ions decrease.

The ionic size of the transition metals is smaller than those of the main group metals.

Size Effect in an Ionic Bond 

Ionic bonds have an electrostatic force that helps ions to hold themselves together in an ionic compound. The strength of an ionic bond depends on the charge that an ion has and the distance between those charged particles. As we all know that the size of transition elements are large, thus the size of ions are also larger. Larger ions make a weaker ionic bond because of the greater distance between its electrons and the nucleus that have opposite charges.

Variation in Atomic and Ionic Sizes of Transition Metals

The addition of new shells increases the atomic and ionic size as the atomic number increases down the group. As a result, the atomic radii of elements in the second transition series are greater than those of the first transition series’ corresponding elements. The atomic and ionic sizes of elements of the second and third transition series are almost the same because of the intervention of the 4 f-orbitals which must be filled before the 5d series of elements begin. Due to lanthanide contraction, the filling of 4f before 5d orbital shows regular decreases in atomic and ionic size. Example: Zx and Hf have largely similar chemical properties and have nearly the same atomic and ionic size because of contraction in lanthanide. The lanthanide contraction is because of the imperfect shielding of one electron by another in the same set of orbitals. However, the shielding of one 4f electron by another is less than one d-electron by another, and as the nuclear charge increases along with the series, there are fairly regular decreases in the size of the entire 4f11.

Trends in Atomic and Ionic Size of the Transition Metals 

Atomic and ionic sizes of the transition series decrease from left to right due to an increase in nuclear charge. However, the decrease in atomic and ionic size is very small and non-uniform. It decreases from group-3 to group-10 and again increases towards the end of the series due to inter electronic repulsion among (n-1) d-electrons.

On moving down the group, atomic and ionic sizes of the transition elements increase. Third transition series elements (except first member La) have nearly the same atomic radii as that of second transition series elements, due to lanthanoid contraction.

The decrease in atomic and ionic size coupled with an increase in atomic mass results in a general increase in the density of these elements. Thus, from titanium (Z = 22) to copper (Z= overline 29 ), a significant increase in the density may be noted.

Conclusion

In books, we have considered the physical properties of transition metals as the main regularities of adsorption and catalysis.

Physical properties play an important role in identifying the transition elements from the list of elements and atomic and ionic size is one of the important physical properties.

Atomic and ionic size is an important physical property of the transition elements. They show a lot of variations in their trends, like the increase of size of the atoms and ions when we move downward in the group and decrease of size when we move upwards. This also affects the bonds present between atoms and ions.