Complex-Forming Tendency of Group 13

All group 13 elements are referred to as the boron family. The periodic table is divided into different groups: the s,p,d, and f blocks. This division is based on the number of valence electrons. For example, if the valence electron occurs in the d subshell, it is grouped under the d block, and so on. 

There are five members in the boron family – boron, gallium, aluminium, indium, and thallium. The electronic configuration of the boron family is Ns²np¹. Aluminium is considered the most abundant element in this group and the third-most abundant on Earth.

This article explains the complex-forming tendency of boron elements. 

General properties of the boron family 

Electronic configuration 

Ns²np¹ is the electronic configuration of Group 13 elements. 

Atomic radii

All the elements in this group have the smallest size due to their nuclear charge compared to the alkaline earth elements. Other than gallium, the atomic radius increases as we go down the group. Gallium has lower atomic radii because of its existing d orbitals, which do not effectively screen the nucleus’s attraction. From B³⁺ TI³⁺, the ionic radius increases in Group 13 elements. 

Density 

From boron to thallium, the density of the elements increases. 

Melting and boiling points 

Group 13 elements have a higher melting point compared to their Group 2 counterparts. But, the melting point decreases as we move down the group and suddenly increases due to structural changes.  

Boron, which is the first element, has a slightly higher melting point as compared to the other family members. This is because of the boron’s three-dimensional structure, in which covalent bonds strongly hold atoms.

Gallium has a lower melting point because it contains molecules of Ga₂ and Ga, which will remain in a liquid state even if the temperature is 2,276 K. Because of this property, gallium is used in high-temperature thermometers. 

Ionisation enthalpy 

The value of ionisation enthalpy is slightly lower in the boron family. The values are lower as compared to alkaline earth metals. Removing electrons from the shell is easy ( Ns²np¹ configuration). 

As we move from boron to aluminium, the ionisation enthalpy values decrease. But the next element, which is gallium, has a higher value than the rest as gallium has poor shielding of intervention of d electrons. This group has no consistency since the values increase as we move to thallium. 

Oxidation state

Gallium, indium, and thallium have oxidation states of +1 and +3, respectively. But, boron and aluminium possess an oxidation state of +3. 

As we move further down the boron family, the oxidation state decreases due to the inert pair effect. This effect doesn’t help the element to occupy the +3 electrons. All the elements after boron and aluminium possess a +1 oxidation state. 

Inert pair effect 

This effect is due to the reluctance of the elements with s electrons to take part in the bonding process. This effect is due to the poor shielding effect of ns². They intervene in the electrons d and f and stop them from forming bonds. 

The inert pair effect increases as we move down the group of 13 elements. That’s why all elements below possess lower oxidation state values.  

Electropositive elements 

Electropositive elements are metallic. Group 13 elements are less electropositive as compared to alkaline earth metals. These elements have smaller sizes and much higher ionisation enthalpy. 

Electropositivity increases as we move from boron to aluminium. But it decreases from gallium to thallium because of the presence of the d and f orbitals, which cause poor shielding. 

Reducing characteristic

Reducing characters decreases as we move down from aluminium to thallium due to an increase in the electrode potential values of M³⁺ and M. The order the group follows is Al > Ga > In > Tl.

Nature of compounds 

When we move downwards in the boron family, the tendency to form ionic bonds increases, boron forms covalent bonds, whereas aluminium forms both covalent and ionic compounds.

On the other hand, Gallium forms ionic compounds with GaCl3, which is anhydrous and forms covalent bonds. 

Complex formation

As the elements of group 13 are smaller in size, they possess stronger complex-forming tendencies as compared to s block elements. 

The complex-forming tendency of group 13 elements 

Elements of the first transition series fulfil all the required conditions for complex-forming tendencies. The cations present in the group have tendencies to form complexes with certain molecules. For example, CO, NO, NH₃.

All molecules and ions that form bonds are called ligands (L). They have more than one lone pair of electrons on their donor atom (the atom that is usually the central atom). They donate this atom to a metal ion or atom during the complex formation, which is done via M←L coordinate covalent bonds. 

This process happens because the electrons are deficient in metal ions in their oxidation state, and/or the atoms present are electron acceptors. 

Due to their small size and high charge density, the metal ions facilitate the formation of complexes. It also depends on the basicity of ligands. This tendency also increases as the positive oxidation state of the metal ion increases. 

The nature of complexes depends on the availability of the metal ions and atoms for bonding. S,p, and d are the types of orbitals. 

Complexes in the transition series are either in the shape of tetrahedral, square, planar, or octahedral structures. These shapes reveal that metal hydrides are hybridised before becoming bonds with ligand orbitals. 

Conclusion

This article explains the complex-forming tendency of group 13 elements. It also mentions examples of the complex-forming tendency. 

The group-13 is also known as the boron family. The elements of this group tend to form complexes. This is due to the presence of d-orbits that have a large number of vacant orbitals. This ultimately leads to variable oxidation states of these compounds. The shape of a complex can be square planar, tetrahedral or octahedral.