Group 4 is the 2nd cluster in the d Block and it contains a number of elements that are considered as transition metals. Altogether, it consists of four elements. The titanium family is another name for this group. Strong corrosion resistance may be attributed to its thick oxide coating. This group also contains rutherfordium, which is artificially synthesized. Group 4 elements have masked inherent reactivity. Their oxidation state is important. When in the highest oxidation state, they are strong oxidizing agents. Their oxidation state is generally less than +2 but they are more electropositive down the column. Elements of group 4 includes Titanium (Ti), Zirconium (Zr), Hafnium (Hf), and Rutherfordium (Rf) (Madelung, 2012).
1. Electronic configuration
General electronic configuration of group 4 is (n-1) ns²nd², while the electronic configuration of this group members is as follows (Xin, et al., 2015).
Ti  1s2 2s2 2p6 3s2 3p6 4s2 3d2 or [Ar] 4s2 3d2
Zr  1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d2 or [Kr] 5s24d2
Hf  1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d2 or [Xe] 4f14 6s²5d²
Rf  1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s24 d10 5p6 6s2 4f14 5d10 6p6 5f14 7s2 [Rn] 5f14 7s2 6d2
2. Trend in the physical properties
Most of the elements in Group 4 are hard, refractory metals. There is evidence of a new kind of metallic bonding based on the melted as well as boiled temperatures of certain metals. They also exhibit corrosion resistance (Clark, Pickard & Ouyang, 2018).
2.1. Atomic and ionic radii
Atomic and ionic radius of group 4 elements increase from top to bottom in group as the distance between nucleus and valence shell increases. But Rutherfordium is excluded in this regard which has larger size than the other member of its group (Madelung, 2012).
Similarly atomic radius group 4 is smaller than those of their group 3 counterparts (Xin, et al., 2015).
Figure 1: Atomic radius of Group 4 elements
Figure 2: Ionic radius of Group 4 elements
2.2. Ionization energy
Ionization energy of group 4 elements decrease from top to bottom in group with exception of hafnium .this decrease in ionization energy is due to increasing number of inner electrons which leads to increasing shielding effect (Clark, Pickard & Ouyang, 2018).
Ionization energy of group 4 elements in kilojoule per mole.
Figure 3: First Ionization Energy of the Group 4 elements
2.3. Melting and boiling point
Melting point of this group elements increase from top to bottom except Rutherfordium which has lower melting point than hafnium while boiling point gradually increase from titanium to Rutherfordium (Madelung, 2012).
Figure 4: Melting and Boiling Points of the Group 4 elements
3. Coordination chemistry of group 4
The coordination chemistry of group 4 elements is primarily based on Lewis acid-base interactions. Each complex has a central metal ion, which is coordinated to a group of ligands. The degree of coordinating complexes might be different according on the kinds of chemicals engaged. Some important coordination complexes of titanium and zirconium are bis(cyclopentadienyl)dichloro Zirconium (IV), TiCl4•2CO(NH2)2, TiCl4•CO(NHCH3)2, TiCl4•2CO(NHCH3)2, 2TiCl4•2NH2CON(C6H5)2.
4. Uses of group 4 elements
Despite their name, group 4 elements have little biological significance. They do not occur naturally as often as some of those others elements in the periodical chart. They have a wide range of applications in industry, such the manufacture of paints and sulfuric acid, both of which need their presence. In fact, sulfuric acid is the most important industrial chemical. Rutherfordium is a substitute for Aluminum with several aeronautical and aviation uses. They have been used in nuclear reactors. Some of them, like titanium, have been used in aircraft. Coordination compounds of group 4 are also used in analytical methods, including spectrophotometry. Moreover, these serve as effective catalytic towards the synthesis of organic molecules. There are a number of applications for coordination complexes, including the transport of oxygen in the blood and pharmaceutical use. In addition, coordination complexes can be used to precipitate metal ions as d complexes (Clark, Pickard & Ouyang, 2018).
Group 4 elements is one of the 18 groups that are naturally occurring hard, refractory metals with masked inherent reactivity. They are protected by a dense oxide layer, which protects them from attack by many acids. These particular substances are referred to as “typical ingredients.” Nearly eighty percent of the surface of the planet is composed of these components alone. They are the most abundant of the chemical elements, and are most widely produced.
He, C., Shi, X., Clark, S. J., Li, J., Pickard, C. J., Ouyang, T., … & Zhong, J. (2018). Complex low energy tetrahedral polymorphs of group IV elements from first principles. Physical Review Letters, 121(17), 175701.
Madelung, O. (Ed.). (2012). Semiconductors: group IV elements and III-V compounds. Springer Science & Business Media.
Tian, H., Xin, F., Wang, X., He, W., & Han, W. (2015). High-capacity group-IV elements (Si, Ge, Sn) based anodes for lithium-ion batteries. Journal of Materiomics, 1(3), 153-169.