What are Group 13 elements?

In the periodic table, group 13 elements exist in the first p-block. There are six elements present in group 13, which include boron (B), aluminum (Al), gallium (Ga), indium (In), thallium (Tl), and element 113 (ununtrium, (Uut)). Group 13 elements are also designated as the boron family.

What are the general trends in the atomic and physical characteristics of Group 13 elements?

Group 13 elements depict a wide difference in their properties. Boron is considered a nonmetal, aluminum is considered a soft, malleable metal, and gallium, indium, and thallium are referred to as metals. The atomic, as well as physical characteristics of group 13 elements, are discussed below.

Atomic radii

Generally, the atomic radii increase down the group. The increasing order of atomic radii of group 13 elements is B<Ga<Al<In<Tl.

Ionization Enthalpy

Ionization energy is the energy estimation needed to eliminate an electron from the orbital of an atom. In general, the ionization enthalpy decreases down the group. However, group 13 elements do not obey the general trend. The order of ionization enthalpy of group 13 elements is B>Tl>Ga>Al>In.


Electronegativity is the estimation of an atom’s ability to attract electrons during bond formation. Generally, the electronegativity decreases down the group. The order of electronegativity of group 13 elements is  B>Tl>In>Ga>Al. 

Oxidation states

The most general oxidation states represented by group 13 elements are +3 and +1. In this group, boron depicts a +3 oxidation state. The ability to exhibit a +1 oxidation state increases down the group due to the inert pair effect. The inert pair effect represents the potency of electrons to exist in an unshared state. The electrons of the outermost orbital display this phenomenon.

Physical Properties

Among group 13 elements, boron has the highest melting point whereas, gallium has the lowest melting point. The boiling point decreases from boron (B) to thallium (Tl). The density of group 13 elements increases from boron (B) to thallium (Tl).

Anomalous behavior of Boron

Boron depicts anomalous properties because it has a small size, high ionization enthalpy, high electronegativity, and absence of the d-orbital. Thus, boron possesses distinct properties from the other group 13 elements.

Chemical properties of Group 13 elements

The chemical characteristics of group 13 elements are discussed below.

Reactivity towards oxygen/air

The chemical reactivity of group 13 elements toward air/oxygen tends to increase down the group. These elements combine with oxygen at high temperatures and furnish trioxides.

The basic character of these trioxides tends to increase down the group. Boron trioxide is basically acidic in nature, aluminum and gallium are considered amphoteric, and indium and thallium are considered basic.

Reactivity toward Acids and Alkalis

Boron is unreactive toward non-oxidizing acids. At high temperatures, boron reacts with strong oxidizing acids and produces boric acid. Boron reacts with strong bases (alkalis) and liberates hydrogen gas. Aluminum and gallium react with alkalis and liberate hydrogen gas.

Reactivity towards Halogens

Group 13 elements combine with halogens and form their trihalides whereas thallium (Tl) combines with halogens and produces monohalides.

Reactivity towards Water

Boron at high temperatures reacts with steam to form boron trioxide. Aluminum decomposes cold water when the oxide layer is absent and liberates hydrogen gas. In the presence of oxygen gas, gallium and indium combine with water. Thallium reacts with moist air to form its hydroxide (TlOH).

Reactivity toward metals

Among all group 13 elements, boron exits as a nonmetal. Thus, only boron reacts with metals to produce borides.

Important compounds of Group 13 elements

The most common and useful compounds of boron are borax, orthoboric acid, and diborane. These compounds are discussed below.


Borax is basically a white crystalline solid and it is considered the most important compound. Borax gets dissolved in water and produces an alkaline solution.

Orthoboric acid

Orthoboric acid  is obtained by acidifying the aqueous solution of borax. 

Orthoboric acid possesses a layered structure. In the structure, BO units are planar and are joined through hydrogen bonds. The structure is shown below.

An image shows the layered structure of boric acid in which the dotted lines depict the hydrogen bonds.
Structure of boric acid


Diborane is basically considered the simplest boron hydride. The treatment of boron trifluoride with lithium aluminum hydride produces diborane. 

Diborane reacts with ammonia and forms a compound which on further heating produces borazine.

In the structure of diborane, both boron atoms are present in-plane; four H-atoms are present at the terminal position, and two H-atoms are at the bridging position. The total number of valence electrons in diborane is 12, and thus, it is electron-deficient. The structure of diborane is shown below.

An image shows the structure of diborane. In the structure, both the B-atoms are in-plane, four H-atoms are at the terminal position, and two H-atoms are at the bridging position.
Structure of diborane

In the structure of diborane, all the four B-H bonds are regular and show two-center two-electron bonding, whereas the two bridging B-H bonds are not regular and they show three-center two-electron bonding. These three-center two-electron bonds are also called banana bonds.

Uses of Boron, Aluminum, and their compounds

The uses of boron, aluminum, and their compounds are discussed below.

  • Boron fibers are basically used in preparing bullet-proof vests.
  • Borax and boric acid are used in the preparation of glass-wool and pyrex.
  • Aluminum and its alloys are used in making pipes, tubes, wires, plates, or foils.

Common Mistakes

Students may confuse group 13 elements with group 14 elements or alkali earth metals. They may compare the trends in the characteristics of group 13 elements with those in group 14 elements, which is incorrect. The characteristics of group 13 elements are distinct from those of group 14 elements.

  • Group 13 elements possess three valence electrons, whereas group 14 elements possess four valence electrons. Alkali earth metals possess two valence electrons.
  • Only the properties of aluminum and beryllium are similar due to the diagonal relationship between beryllium and aluminum.
  • All the elements of group 13 elements are not considered metals, whereas all the elements of alkali earth metals are considered as metal.

Context and Applications

This topic is applicable in the professional exams for both undergraduate and graduate courses, especially for:

Bachelors in Chemistry

Masters in Chemistry

Masters in Pure and Applied Chemistry

Masters in Inorganic Chemistry

Related Concepts

p-block elements

s-block elements


Chemical Bonding

Practice Problems

Q1: Identify the group 13 element that has the largest ionization energy.

(a) Indium

(b) Gallium

(c) Boron

(d) Thallium

Correct option: (c)

Q2: Predict the total number of valence electrons that group 13 elements possesses.

(a) Three

(b) Four

(c) Two

(d) Five

Correct option: (a)

Q3: Among the following, predict the number of non-metallic elements present in group 13.

(a) None

(b) Two

(c) Three

(d) One

Correct option: (d)

Q4: Predict the group 13 element that has the smallest size?

(a) Aluminum

(b) Boron

(c) Gallium

(d) Thallium

Correct option: (b)

Q5: What charge do group 13 elements tend to acquire as ions?

(a) +3

(b) +2

(c) +1

(d) +4

Correct option: (a)

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