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Group-13 Elements: Boron Family | Chemistry Class 12 - NEET PDF Download

What are Group 13 Elements?

The group 13 elements are the first group in the p-block of the periodic table. 

All the elements of group 13 are also called the boron family. The periodic table is segregated into s, p, d and f-blocks. This segregation is done based on the valence electron, if the valence electron falls on the p subshell, it comes in p-block and so on.

Group 13 ElementsGroup 13 Elements

The members of Group 13 elements are:

  • Boron
  • Aluminium
  • Gallium
  • Indium
  • Thallium

The general electronic configuration for the group 13 elements is ns2np1. Al is the most abundant metal and third most abundant element in the earth’s crust.

1. Electronic Configuration

  • Their valence shell electronic configuration of this group is ns2np1. Here is the detailed electronic configuration of all the elements.

    Group-13 Elements: Boron Family | Chemistry Class 12 - NEET

2. Atomic Radii and Ionic Radii

  • Group 13 elements have a smaller size than those of alkaline earth metals due to greater effective nuclear charge, Zeff’
    Group-13 Elements: Boron Family | Chemistry Class 12 - NEET
  • Atomic radii increase on going down the group with an anomaly at gallium (Ga). Atomic radius increases down the group (Tl has the largest atomic radius.) An unexpected decrease in the atomic size of Ga is due to the presence of electrons in d-orbitals which do not screen the attraction of the nucleus effectively. The ionic radii regularly increase from B3+ to TI3+.

3. Density


It increases regularly on moving down the group from B to Tl.

4. Melting and Boiling Points

  • The Melting point and boiling point of group 13 elements are much higher than those of group 2 elements.
    Group-13 Elements: Boron Family | Chemistry Class 12 - NEET
  • The melting point decreases from B to Ga and then increases, due to structural changes in the elements. Boron has a very high melting point because of its three-dimensional structure in which B atoms are held together by strong covalent bonds.
  • The low melting point of Ga is due to the fact that it consists of Ga2 molecules, and Ga remains liquid upto 2276 K. Hence, it is used in a high-temperature thermometer.
    Question for Group-13 Elements: Boron Family
    Try yourself:Which of the following element has the highest melting point?
    View Solution

5. Ionisation Enthalpy (IE)

  • The initial ionization enthalpy values of Group 13 elements are comparatively lower than those of the corresponding alkaline earth metals. This can be attributed to the ease of electron removal, especially considering the [ns2 np1 configuration]. 
  • The trend of decreasing ionization energy persists as one moves down the group. This is primarily due to the electrons being farther from the core, making them easier to remove. However, it's worth noting that thallium (Tl) does not conform to this trend.

Trends & Properties of Group 13 elementsTrends & Properties of Group 13 elements

  • Upon descending the group, the ionization enthalpy decreases from boron (B) to aluminum (Al). Nevertheless, gallium (Ga), the subsequent element, exhibits a slightly higher ionization enthalpy than Al. 
  • This anomaly can be attributed to the inefficient shielding provided by intervening d-electrons. The trend then resumes with a decrease in ionization enthalpy for indium (In) before concluding with an increase in the last element, thallium (Tl).

6. Oxidation States

  • B and Al show an oxidation state of +3 only while Ga, In and Tl exhibit oxidation states of both +1 and +3.
  • As we move down in group 13, due to the inert pair effect the tendency to exhibit +3 oxidation state decreases and the tendency to attain +1 oxidation state increases. Stability of +1 oxidation state follows the order Ga < In < Tl.
  • Inert pair effect is the reluctance of the s-electrons of the valence shell to take part in bonding. It occurs due to poor shielding of the ns2 – electrons by the intervening d and f – electrons. It increases down the group and thus, the lower elements of the group exhibit lower oxidation states.

7. Electropositive (Metallic) Character

  • These elements are less electropositive than the alkaline earth metals due to their smaller size and higher ionisation enthalpies.
  • On moving down the group, the electropositive character first increases from B to Al and then decreases from Ga to Tl, due to the presence of d and f-orbitals which causes poor shielding.

8. Reducing Character

  • It decreases down the group from Al to Tl because of the increase in electrode potential value for M3+ / M.
  • Therefore, it follows the order: AI > Ga > In > Tl

9. Complex Formation


Due to their smaller size and greater charge, these elements have a greater tendency to form complexes than the s-block elements.

10. Nature of Compounds


The tendency of the formation of ionic compounds increases from B to Tl. Boron forms only covalent compounds whereas Al can form both covalent as well as ionic compounds. Gallium forms mainly ionic compounds, although anhydrous GaCI3 is covalent.

Chemical Properties of Group 13 Elements

Group 13 elements, also known as the boron group, exhibit a variety of chemical properties that are influenced by their electronic configurations and position on the periodic table. Here are some notable chemical properties of Group 13 elements:

1. Action of Air 

  • Crystalline boron is unreactive whereas amorphous boron is reactive. It reacts with air at 700°C as follows-
    4B + 3O2 → 2B2O3
    2B + N2 → 2BN
  • Al is stable in air due to the formation of the protective oxide film.
    4Al + 3O2 → 2Al2O3
  • Thallium is more reactive than Ga and In due to the formation of unipositive ion, Tl+.
    4Tl + O2 → 2Tl20

2. Reaction with Nitrogen

The chemical reaction of boron and Aluminium with nitrogen at a high temperature is as follows :

3. Action of Water 

  • Both B and Al do not react with water but amalgamated aluminium reacts with H2O evolving H2.
    2Al(Hg) + 6H2O → 2AI(OH)3 + 3H2 + 2Hg
  • Ga and In do not react with pure cold or hot water but Tl forms an oxide layer on the surface.

4. Reaction with Alkalies 

  • Boron dissolves in alkalies and gives sodium borates.
    Group-13 Elements: Boron Family | Chemistry Class 12 - NEET
  • Aluminium also reacts with alkali and liberates hydrogen.Group-13 Elements: Boron Family | Chemistry Class 12 - NEET

5. Reaction with Carbon

Aluminium carbide is ionic and forms methane with water.

6. Hydrides 

  • Elements of group 13 do not combine directly with H2 to form hydrides, therefore their hydrides have been prepared by indirect methods, e.g
  • Group-13 Elements: Boron Family | Chemistry Class 12 - NEETBoron forms a number of hydrides, they are known as boranes. Boranes catch fire in the presence of oxygen.B2H6 + 3O2 → B2O3 + 3H2O; & ΔcH° = – 1976 kJ mol-l
  • Boranes are hydrolysed by water.
    B2H6 + 6H2O → 2H3BO3 + 6H2
  • Boranes are stable but the stability of hydrides of Al, Ga, In, and Tl decreases on moving down the group because the strength of the M-H bond decreases.

Structure of diborane: 

  • BH3 does not exist as such, but exists as a dimer, i.e; B2H6(diborane].

Group-13 Elements: Boron Family | Chemistry Class 12 - NEET

Diborane
  • In the above structure, B atoms are in sp3 – hybrid state. There are six B-H bonds out of which four B-H bonds are normal bonds present in the same plane while rest two B-H bonds behave as bridge bonds, ie; 3c – 2e (three centre-two electrons, also known as a banana bond) and present above and below the plane of the molecules which do not have a sufficient number of electrons to form covalent bonds.
  • Aluminium (Al) forms a polymeric hydride of general formula (AlH3)x which decomposes into its elements on heating.

Question for Group-13 Elements: Boron Family
Try yourself:Diborane is a ____________
View Solution

7. Oxides 

  • Except for Tl, all the elements of group 13 form oxides or general formula M2Oon heating with oxygen.
    Group-13 Elements: Boron Family | Chemistry Class 12 - NEET
  • Tl forms thallium (l) oxide. Tl2O is more stable than thallium (III) oxide TI2O3 due to the inert pair effect.

8. Nature of Oxides and Hydroxides 

  • B(OH)3 or H3BO3 is soluble in water, while other hydroxides are insoluble in water.
  • On moving down the group, there is a change from acidic to amphoteric and then to the basic character of oxides and hydroxides or group 13 elements.

9. Halides

  • All the elements of the boron family (except Tl) form trihalides of type MX3.
    Group-13 Elements: Boron Family | Chemistry Class 12 - NEET
  • All the boron trihalides [(BX3) and aluminium trihalides AlX3 (except AIF3 which is ionic) are covalent compounds. AlX3 exists as a dimer while BX3 is a monomer because the boron atom is too small to coordinate with four large halide ions. 
  • The energy released during the formation of the bridge structure is not sufficient for the cleavage of the typical pπ – pπ bond in BF3.
    Group-13 Elements: Boron Family | Chemistry Class 12 - NEET
  • BF3 is a colourless gas, BCl3 and BBr3 are colourless fuming liquids and BI3 is a white solid at room temperature.
  • Trihalides of group 13 elements behave as Lewis acids because of their strong tendency to accept a pair of electrons. The relative strength of Lewis acids of boron trihalides is: BF3 < BCI3, < BBr3, < BI3.
    This is due to pπ – pπ back bonding in BF3 which makes it less electron deficient.
  • The halides of group 13 elements behave as Lewis acids and the acidic character is BX3 > AIX3 > GaX3 > InX3 (where, X = Cl, Br or I)
    TICI3 decomposes to TICl and Cl2 and hence acts as an oxidising agent.Group-13 Elements: Boron Family | Chemistry Class 12 - NEET

Anomalous Behaviour of Boron

Boron shows anomalous behaviour with the other members of the group, due to the following reasons:

  • The smallest size in the group.
  • High ionisation energy.
  • Highest electronegativity in the group.
  • Absence of vacant d-orbital.

Few Points of Difference

  • It is non-metal while other members of the group are metallic.
  • It shows allotropy while other members do not.
  • It has the highest melting point and boiling point in group 13.
  • It forms only covalent compounds while other members form both ionic and covalent compounds.
  • The halides of boron exist as monomers while AlCl3 exists as a dimer.
  • The oxides and hydroxides of boron are weakly acidic while those of aluminium are amphoteric and those of other elements are basic.
  • It can be oxidised by concentrated HNO3 while aluminium becomes passive due to the formation of an oxide layer on the surface.
    Group-13 Elements: Boron Family | Chemistry Class 12 - NEET

Diagonal Relationship between Boron and Silicon

Boron exhibit resemblance with its diagonal element silicon of group 14.

Diagonal RelationshipDiagonal Relationship

  • Both Band Si are non-metals.
  • Both are semi-conductors.
  • Both Band Si form covalent hydrides, i.e.. boranes and silanes respectively.
  • Both form covalent, and volatile halides which fume in moist air due to the release of HCI gas.
    BCI3 + 3H2O → H3 BO3 + 3HCl
    SiCl4 + 4H2O → Si(OH)4 + 4HCl
    Question for Group-13 Elements: Boron Family
    Try yourself:Which of the following property is not a similarity between Boron and silicon?
    View Solution
  • Both form solid oxides which get dissolve in alkalies forming borates and silicates respectively.
  • Both react with electropositive metals and give binary compounds, which yield a mixture of boranes and silanes on hydrolysis.
    Question for Group-13 Elements: Boron Family
    Try yourself: Boron shows a diagonal relationship with ____________
    View Solution

Metallurgy of Boron

Occurrence


It does not occur in a free state. Its important minerals are

  • Borax (or Tineal), Na2B4O7 * 1OH2O
  • Kernite, Na2B4O7 * 4H2O
  • Orthoboric acid, H3BO3

Isolation


Elemental boron is obtained by the following methods:

  • By reduction of boric oxide with highly electropositive metals like K, Mg, AI, Na etc, in the absence of air.
    Group-13 Elements: Boron Family | Chemistry Class 12 - NEET
  • By the reaction of boron halides with hydrogen.
    Group-13 Elements: Boron Family | Chemistry Class 12 - NEET

Uses of Boron

  • As a semi-conductor.
  • Boron steel rods are used to control nuclear reactions.
    5B10 + 0n15B11

    Question for Group-13 Elements: Boron Family
    Try yourself:Which of the following is not a use of Boron?
    View Solution

Compounds of Boron

1. Borax or Sodium Tetraborate Decahydrate[Na2B4O7.1OH2O]


Preparation
It occurs naturally as tineal in dried up lakes. It is obtained by boiling mineral colemanite with a solution of Na2CO3.
Group-13 Elements: Boron Family | Chemistry Class 12 - NEETNaBO2 can be removed by passing CO2 through it.
4NaBO2 + CO2 → Na2CO3 + Na2B4O7
Properties
(i) Its aqueous solution is basic in nature.
Na2B4O7 + 7H2O → 2NaOH + 4H3BO3
(ii) On heating with ethyl alcohol and conc. H2SO4. It gives volatile vapours of triethyl borate which burn with a green flame.
Group-13 Elements: Boron Family | Chemistry Class 12 - NEET
(iii) Action of heat:
Group-13 Elements: Boron Family | Chemistry Class 12 - NEETBorax bead is used for the detection of coloured basic radicals under the name borax bead test e.g.,
Group-13 Elements: Boron Family | Chemistry Class 12 - NEET

Group-13 Elements: Boron Family | Chemistry Class 12 - NEET2. Boric Acid or Orthoboric Acid [H3BO3 or B(OH)3]


Preparation
By treating borax with dil. HCl or dil. H2SO4.
Na2B4O7 + 2HCl + 5H2O → 2NaCI + 4H3BO3
Properties
(i) It is a weak monobasic acid (Lewis acid).
H3BO3 + 2H2O → [B(OH)4]– + H3O+
(ii) With C2H5OH and cone H2SO4, it gives triethyl borate.
Group-13 Elements: Boron Family | Chemistry Class 12 - NEET(iii) Heating Effect:
Group-13 Elements: Boron Family | Chemistry Class 12 - NEETUses
It is used as an antiseptic and eye lotion under the name ‘boric lotion’, and as a food preservative.3. Borazine or Borazole, [B3N3H6]It is a colourless liquid having a six-membered ring of alternating B and N atoms. It is also called ‘inorganic benzene’. It is prepared by B2H6 as follows:
Group-13 Elements: Boron Family | Chemistry Class 12 - NEETThe π electrons in borazine are only partially delocalised. It is more reactive than benzene.

Compounds of Aluminium

1. Anhydrous Aluminium Chloride [AlCl3 or Al2Cl6]


Preparation


(i) It cannot be prepared by heating AICI3. 6H2O.Group-13 Elements: Boron Family | Chemistry Class 12 - NEET(ii) By passing dry chlorine or HCl gas over heated Al.Group-13 Elements: Boron Family | Chemistry Class 12 - NEET(iii) By heating a mixture of alumina and carbon in a current of dry chlorine.Group-13 Elements: Boron Family | Chemistry Class 12 - NEET

Properties


(i) AlC13 fumes in moist air due to hydrolysis.
AlC13 + 3H2O → Al(OH)3 + 3HCI
(ii) It behaves as Lewis acid.

Uses


It is used as a catalyst in Friedel-Craft reaction and as a mordant dye.

2. Aluminium Oxide or Alumina [AI2O3]

It is the most stable compound of aluminium and occurs in nature as colourless corundum and several coloured oxides, (it present in combination with different metal oxides) like ruby (red), topaz (yellow), sapphire (blue), and emerald (green), which are used as precious stones (gems).

Alum:

The term alum is given to double sulphates of the type X2SO4 * Y2(SO4)3 * 24H2O where, X represents a monovalent cation such as Na+, K+ and NH+4, while Y is a trivalent cation such a Al3,Cr3+, Fe3+ and Co3+(Li+ does not form alum).

Potash AlumPotash Alum

Question for Group-13 Elements: Boron Family
Try yourself:What is the chemical formula of alumina and anhydrous aluminium chloride?
View Solution

Some important alums are:

(i) Potash alum K2SO4 * Al2(SO4)3 * 24H2O

(ii) Sodium alum Na2SO4 * A12(SO4)3. 24H2O

(iii) Ammonium alum (NH4)2SO4 * AI2(SO4)3 24H2O

(iv) Ferric alum (NH4)2SO4 * Fe2(SO4)3 24H2O

Potash alum is prepared in the laboratory by mixing hot equimolar quantities of K2SO4 and Al2(SO4)3. The resulting solution on concentration and crystallisation gives potash alum.

Note:

(i) A mixture of Al powder NH4NO3 is called ammonal and is lUed in bombs.

(ii) Al is the chief constituent of silver paints.

(iii) A12(SO4)3 1.8 used for making fireproof clothes.

Question for Group-13 Elements: Boron Family
Try yourself:Which of the following is used as a catalyst in Friedel craft reaction?
View Solution

3. Thermite


A mixture of aluminium powder and ferric oxide in the ratio 1: 3.

4. Aluminium Sulphate, Al2(SO4)3


It is used for obtaining H2S in pure form and for making fireproof clothes.

5. Alloys of Aluminium


Alums

The term alum is given to double sulphates of the type X2SO4, Y2(SO4)3. 24H2where X represents a monovalent cation such as Na+,K+ and NH Rb+, Cs+, Ag+ while Y is a trivalent cation such a Al3+, Cr3+ and Fe3+, Co3+, Ga3+, V3+, Ti3+. (Li+ is too small to be accommodated in the lattice).

General formula
Group-13 Elements: Boron Family | Chemistry Class 12 - NEET or Group-13 Elements: Boron Family | Chemistry Class 12 - NEET
Some important alums are:
1. Potash alum K2SO4. Al2(SO4)3. 24H2O
2. Sodium alum Na2SO4. Al2(SO4)3. 24H2O
3. Ammonium alum (NH4)2SO4. Al2(SO4)3. 24H2O
4. Ferric alum (NH4)2SO4. Fe2(SO4)3. 24H2O
5. Chrome alum K2SO4. Cr2(SO4)3. 24H2O

Out of these, potash alum is the most important which is prepared in the laboratory by mixing hot solutions of equimolar quantities of K2SO4 and Al2(SO4)3. The resulting solution on concentration and crystallization gives potash alum (emperical formula is KAl(SO4)2.12H2O). 

Pseudo Alums

When monovalent element of ordinary alums is replaced by a bivalent element eg. Mn2+, Fe2+, Mg2+, Cu2+ or Zn2+the alums are called pseudo alums.
Examples: 
1. FeSO4.Al2(SO4)3.24H2→ Ferrous aluminium pseudo alum 
2. MnSO4.Al2(SO4)3.24H2O → Manganese aluminium pseudo alum

Properties

  • Potash alum is a white crystalline compound. 
  • The aqueous solution of all alums is acidic due to hydrolysis of Al2(SO4)3, Cr2(SO4)3 or Fe2(SO4)as given below
Al2(SO4)3 + 6H2O → 2Al(OH)3 + 3H2SO4
  • On heating all alums lose water of crystallization 
    and swell up. The anhydrous alum is known as burnt alum.
  • Ionisation of aqueous solution of a double salt is as
K2SO4. Al2(SO4)2. 24H2O → K+ + 2Al3+ + 3SO + 24H2O

Uses

  • In purification of water.
  • For sizing of paper.
  • As a styptic to stop bleeding.
  • As a mordant in dyeing and tanning of leather.
The document Group-13 Elements: Boron Family | Chemistry Class 12 - NEET is a part of the NEET Course Chemistry Class 12.
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FAQs on Group-13 Elements: Boron Family - Chemistry Class 12 - NEET

1. What are the physical properties of Group 13 elements?
Ans. Group 13 elements, also known as the Boron family, include Boron (B), Aluminum (Al), Gallium (Ga), Indium (In), and Thallium (Tl). They exhibit some common physical properties such as having low melting and boiling points, except for Thallium which has a relatively higher melting point. These elements are generally poor conductors of electricity and have metallic luster. They also possess low densities and are relatively soft metals.
2. What are the trends in physical properties of Group 13 elements?
Ans. The physical properties of Group 13 elements show some trends as we move down the group. The atomic radius and metallic character increase down the group, while ionization energy and electronegativity decrease. This trend can be attributed to the increase in the number of energy levels and shielding effect provided by inner electrons.
3. What are the chemical properties of Group 13 elements?
Ans. Group 13 elements exhibit both metallic and non-metallic behavior in their chemical properties. They have a tendency to lose three valence electrons to form +3 cations. These elements react with non-metals to form binary compounds. Boron, however, shows some unique chemical properties due to its small size and electron deficiency. It often forms covalent compounds instead of ionic compounds.
4. What is the anomalous behavior of Boron?
Ans. Boron exhibits some anomalous behavior compared to other elements in Group 13. It is a non-metal, unlike the rest of the group which are metals. Boron has a higher melting point, lower density, and is a poor conductor of electricity. These differences arise due to its small size, electron deficiency, and unique bonding characteristics.
5. What is the diagonal relationship between Boron and Silicon?
Ans. Boron and Silicon show a diagonal relationship in their properties due to their similar atomic size and electronic configurations. Both elements tend to form covalent compounds instead of ionic compounds. They also exhibit similarities in their oxides, hydrides, and acid-base behavior. This diagonal relationship is often explained by the concept of effective nuclear charge and the importance of size and electron configuration in determining chemical properties.
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