Boron group (Group 13)
Group 13 of the periodic table — boron, aluminium, gallium, indium, thallium and nihonium — a family with three valence electrons, varied bonding, important industrial uses and notable chemical trends.
Overview
The boron group, also referred to as Group 13 (or IIIA) on the periodic table, comprises six chemical elements that share a common outer-shell electron count of three. Members range from the nonmetallic or semimetallic boron to metallic aluminium, gallium, indium and thallium, and the synthetic element nihonium. Their chemistry reflects a blend of covalent and metallic behavior and supports many technological applications.
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Members and basic characteristics
- Boron (B) — a hard, covalently bonded metalloid that forms boranes and borides; behaves quite differently from the metals of the group. Boron is essential in some materials applications.
- Aluminium (Al) — a lightweight, abundant metal used structurally and in packaging.
- Gallium (Ga) — a soft metal notable for its low melting point and role in semiconductors.
- Indium (In) — used in electronics, notably transparent conductive coatings.
- Thallium (Tl) — a dense metal with historic applications but significant toxicity.
- Nihonium (Nh) — a short-lived, laboratory-produced element with no commercial uses.
Common chemical features include a preference for the +3 oxidation state, with heavier members increasingly exhibiting a +1 state because of the inert-pair effect. Reactivity and metallic character generally increase down the group, while atomic and ionic sizes also grow.
History and development
Discovery and isolation of these elements occurred over two centuries: boron and aluminium were isolated in the early 1800s; gallium, indium and thallium were identified in the mid- to late-1800s as spectroscopy and analytical chemistry advanced; nihonium was synthesized in the early 21st century. The group has been studied both for fundamental chemistry and for advancing materials science.
Uses, examples and notable facts
Applications exploit both chemical and physical diversity: boron compounds strengthen glass and ceramics and appear in advanced composites; aluminium is central to construction and transportation; gallium and indium are critical in electronic and optoelectronic devices (for example, gallium arsenide and indium tin oxide); thallium’s use is limited by toxicity; nihonium remains purely a subject of research. The group also illustrates important chemical concepts such as varied bonding types, the inert-pair effect and trends in electronegativity and ionization energy.
For concise element tables, comparative properties and further reading, see general references on groups of the periodic table and element-specific entries: group elements.
Occurrence
The earth's crust consists of 7.3 % elements of the boron group, which are mostly present as oxides. Aluminium, the most common metal in the earth's crust, accounts for 99.94 % of this. The other elements of the boron group are rare.
This 0.06% is broken down as follows:
- 51 % Boron
- 46 % Gallium
- 3 % Indium
- 0,2 % Thallium
Minerals containing aluminium:
· 
Bauxite (mineral mixture)
· 
Corundum (Al2O3)
· 
Ruby (form of corundum)
· 
Raw sapphire (form of corundum)
No element of the boron group makes a solid appearance.
Properties
The first element of the group, boron, differs substantially from the other elements of the boron group because of its semimetallic properties, all of which are metals and similar in properties to the alkaline earth metals.
Physical properties
With increasing atomic number, atomic mass, atomic radius and ionic radius increase. Boron has the highest melting point with 2076 °C, gallium the lowest with only 29.76 °C (body temperature: ~37 °C). In between are indium (156.6 °C), thallium (304 °C) and aluminum (660.32 °C). The boiling points decrease from top to bottom: Boron has the highest value at 3927 °C, followed by aluminium (2467 °C), gallium (2204 °C), indium (2072 °C) and finally thallium (1473 °C).
As the atomic number increases, the density increases, while the hardness decreases. Boron has the lowest density of 2.460 kg/dm3 and the highest Moh's hardness of 9.3. Thallium has exactly the opposite density of 11.850 kg/dm3 and a Moh's hardness of only 1.2.
Aluminium has the highest electrical conductivity at 37.7 MS/m (about one third less than copper (58 MS/m)), while boron has the lowest at 0.10 mS/m.
The 1st ionization energy decreases with increasing atomic number from 8.298 eV for boron to 5.786 eV for indium, but gallium is second with 5.999 eV (instead of aluminum with 5.968 eV). Thallium has an increased value of 6.108 eV.
The electronegativity is highest with boron at 2.0, reaches a temporary low point at 1.5 with aluminium and then rises again to 1.8, the value of gallium. In the further course, the electronegativity decreases again to the value 1.4 (thallium).
At very low temperatures, aluminium, gallium, indium and thallium conduct electric current without resistance. They become superconductors.
| Item | Melting point in K | boiling point in K | Density in kg/m3 | Mohs hardness | El. conductivity in S/m |
| Boron | 2349 | 4200 | 2460 | 9,3 | 1 · 10−4 |
| Aluminium | 933,47 | 2740 | 2700 | 2,75 | 37,7 · 106 |
| Gallium | 302,91 | 2477 | 5904 | 1,5 | 6,76 · 106 |
| Indium | 429,75 | 2345 | 7310 | 1,2 | 11,6 · 106 |
| Thallium | 577 | 1746 | 11850 | 1,2 | 6,17 · 106 |
Electron configuration
The electron configuration is [X] ys2yp1. The X stands for the electron configuration of the noble gas one period higher, and for the y the period in which the element is located must be inserted. Starting with gallium, there is also a (y-1)d10 orbital; and starting with thallium, there is also a (y-2)f14 orbital.
For the individual elements, the electron configurations are:
- Boron: [ He ] 2s22p1
- Aluminium: [ Ne ] 3s23p1
- Gallium: [ Ar ] 3d104s24p1
- Indium: [ Kr ] 4d105s25p1
- Thallium: [ Xe ] 4f145d106s26p1
- Nihonium (calculated): [ Rn ] 5f146d107s27p1
The oxidation state is +3. Only thallium and indium also occur with the oxidation state +1, which in the case of thallium is even more frequent than +3.
Chemical reactions
In the following equations the Me stands for an element from the third main group (boron group).
- Reaction with oxygen:
Thallium also forms Tl2O
- Reaction with hydrogen (not spontaneous):
Only boron and aluminium react to form (always covalent) hydrogen compounds. In the case of boron, the structurally diverse boranes with diborane (B2H6) as the simplest representative are formed by three-centre bonding; the hypothetical monomer BH3 does not exist. AlH3 molecules are connected by hydrogen bonds.
- Reaction with water:
Only aluminium releases hydrogen from water. On contact with air/oxygen, however, aluminium very quickly forms a passivation layer which protects the metal from reacting with water.
- Reaction in alkaline:
- 
- 
In the alkaline, no Al(OH)3 is formed, but the aluminate ion Al(OH)4-.
Thallium also forms TlCl.
Questions and answers
Q: What is the boron group?
A: The boron group, also known as Group III and Group 13, is a group of elements on the periodic table.
Q: Are most members of the boron group metals or non-metals?
A: Most of its members are poor metals, except for boron.
Q: What is the classification of boron in the boron group?
A: Boron is a semimetal.
Q: Are all elements in the boron group metals?
A: No, the rest of the elements are soft metals.
Q: Can boron be classified as a metal?
A: No, boron is not a metal but rather a semimetal.
Q: What is the main element in the boron group?
A: The main element in the boron group is boron.
Q: Is boron the only non-metal element in the boron group?
A: Yes, boron is the only non-metal element in the boron group.
Related articles
Author
AlegsaOnline.com Boron group (Group 13) Leandro Alegsa
URL: https://en.alegsaonline.com/art/13148