The Boron Family in the Periodic Table

Group 13 Boiling point 4000oC, 4273K, 7232oF
Period 2 Melting point 2077oC, 2350K, 3771oF
Block p Relative atomic mass 10.81
Atomic number 5 Density (g cm-3) 2.34
State at 20oC Solid Key isotopes 11B
Electronic configuration [He] 2s2 2p1 CAS number 7440-42-8

Let us know something about boron family

Boron 1

Boron got its name from the Arabic word ‘buraq’ which is the name of borax. It belongs to the 13th group of the p block element. The elements of the 13th group are boron, aluminium, gallium, indium, and thallium. They all are metallic in nature except boron which is a metalloid. All of them have 3 electrons in the outermost shell which has the electronic configuration of ns2np1. There are two oxidation states (+3 and +1) of boron family.

Boron is a non-metal but the second element is aluminium which is a metal. Gallium, indium, and titanium are almost metallic in nature. Aluminium is also one of the most important members of the boron family which has an atomic number of 13 and chemical symbol is Al. It is very expensive to produce aluminium because for electrolysis of one mole of aluminium, we require 3 moles of electron and thus a huge amount of energy is used.

Table of Content

Electronic Configuration of Boron Family

The general electronic configuration of Boron family is ns2np1

Element Atomic Number Electronic Configuration
Boron (B) 5 [He] 2s22p1
Aluminium (Al) 13 [Ne] 3s23p1
Gallium (Ga)  31 [Ar] 3d104s24p1
Indium (In) 49 [Kr] 4d105s25p1
Thallium (Tl) 81 [Xe] 4f14 5d106s26p1

Atomic and Ionic Radii of Boron Family

Element Atomic Radius/pm Ionic Radius(M3+)/pm
Boron (B) 85 27
Aluminium (Al) 143 53.5
Gallium (Ga)  135 62.0
Indium (In) 167 80.0
Thallium (Tl) 170 88.5

As we move from top to bottom in the periodic table the atomic and ionic radius increase because down the group number of new shells are added as a result  the magnitude of screening effect increases which decreases the attraction between valence electrons and nucleus of the atom.

Note: Some anomalies observed:

There is a sharp increase in atomic and Ionic radius from Boron to Aluminium

In case of Al(2,8,3)  there is a greater Screening effect by the 8 electrons present in the penultimate shell resulting in decreased effective nuclear charge. Therefore, the atomic radius is more than the expected value. However there is no such effect observed for B atom (2,3) since it has only two shells. 

The atomic radius of Gallium is less than that of  Aluminium.

In the Gallium the atomic radius decreases as compared to the Aluminum because of the presence of 3d elements. Since d-orbitals have less shielding effect, it increases the effective nuclear charge of Ga. However in such cases it is not observed in the case of  ionic radius. It increases regularly.

Ionisation Enthalpy of Boron Family

Elements Ionisation enthalpy(△H1)/kJ mol-1 
Boron (B) 800
Aluminium (Al) 577
Gallium (Ga)  578
Indium (In) 558
Thallium (Tl) 590

The ionisation value from B to Al decreases sharply because of the bigger size of the Al atom. But the element Ga ten electrons present in the 3d subshell which do not screen as much as is done by s and p electrons, therefore, there is an unexpected increase in the magnitude of effective nuclear charge resulting in increased value. The same explanation can be offered in moving from In to Tl. The latter has fourteen 4f electrons with very poor shielding effect. This also results in an unexpected increase in the effective nuclear charge of Tl 

Oxidation State of  Boron Family

The following trends are observed in the oxidation states of Boron Family

  1. The first two elements Boron and Aluminium show +3 oxidation state.
  2.  The remaining elements Gallium, Indium and Thallium show both +1 and +3 oxidation states.
  3. The stability of +3 oxidation state decreases from Aluminium onwards and the last element Thallium, +1 oxidation is more stable than +3. 
  4. So that TlCl is more stable than TlCl3.

The above trend is explained with the help of the Inert pair effect.

Inert pair effect: 

As a result  of the inert pair effect,  the electron pair representing the valence s- electrons is more exposed to the nucleus than the p-electrons. In other words, these are held tightly by the nucleus and are not readily available for the bond formation. However, valence p-electrons are available for the same. The inert pair effect becomes more predominant as we go down the group as a result the valence p-electrons will be more available accounting for the +1 oxidation state. The inert pair effect is maximum in the last element thallium (Tl) in the boron family. Therefore TlCl is more stable than TlCl3.

Chemical Properties of Boron Family

Formation of Hydrides: The elements present in group 13 do not combine directly with hydrogen to form hydrides. However, a number of hydrides of these have been prepared indirectly. Boron, the first member of the family, forms a number of hydrides called Boranes.
These are two types, 

BnHn+4  :  B2H6 ,B3H7,  B4H8 etc. 

BnHn+6  : B4H10, B5H11, B6H12 etc.

Out of the boranes, the most important is diborane is prepared following way:

By the reduction of boron trifluoride with LiAlH4 in diethyl ether as

            4BF +  3LiAlH4 → 2 B2H6  + 3LiF  + 3AlF3

To learn more about the chemical properties of Boron family you may visit the following link:  Chemical Properties of  The Borane Family 

Do you know why aluminium does not react with water?

A protected layer of Al2O3 is formed due to which it does not react with water. This process is also called as anodising.

Gallium which has chemical formula Ga and atomic number 31 and has the second-lowest melting point after mercury and it can persist in a liquid phase at larger temperature than any other substance. Gallium is very important industrially as it forms Gallium arsenide which converts light directly into electricity.

Indium is also one of the p block element with atomic number 49. Indium is also soft malleable metal just like gallium. In the acids indium is soluble but at room temperature, it does not react with oxygen. Indium is used for increasing the strength of metals and is also used in making alloys.

Thallium which has chemical formula Tl is a heavy element and is also very stable in +1 oxidation state. Even though it’s poisonous then also it is used in high-temperature superconductors.

There is a diagonal relationship between beryllium and aluminium which is that when it reacts with water both of these compounds produce hydronium ions, and one more similarity between these two is that both of them are amphoteric in nature.

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Frequently Asked Questions-FAQs


1. Why is Group 13 called the boron family?

Boron is the first element of the group-13 elements. So that group 13 is named as Boron Family. The remaining elements of the Boron family are Aluminium (Al), Gallium (Ga), Indium (In) and Thallium (Tl).


2. How does boron differ from other members of Group 13 elements?

Due to its smaller size and unavailability of d-electrons boron is found to exhibit properties which are in contrast to the other elements of the boron family. These properties are known as anomalous properties of boron. Some of these are the maximum covalency of boron is 4 due to the absence of d orbitals. The boron oxides and hydroxides are acidic in nature, whereas the other elements in the family form oxides and hydroxides which are amphoteric in nature.


3. Which element shows diagonal relationship with boron?

Boron and silicon are diagonally related with each other.


4. What is the reason for the inert pair effect?

The electron pair representing the valence s- electrons is more exposed to the nucleus than the p-electrons. In other words, these are held tightly by the nucleus and are not readily available for the bond formation. However, valence p-electrons are available for the same. This effect is called the inert pair effect.

Recommended Video

p-Block Elements Chemistry – Boron Family

Test your knowledge on boron family in the periodic table


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