Boron group

The boron group is a specific family of chemical elements located in group 13 of the periodic table.

This group is found within the p-block and includes six distinct elements. These are boron (B), aluminium (Al), gallium (Ga), indium (In), thallium (Tl), and the synthetic element nihonium (Nh). Scientists often refer to this group as the triels. This name comes from the Latin prefix "tri-", which means three. It describes the three valence electrons found in the outermost shells of every element in this group. These electrons are essential because they dictate how these elements behave during chemical reactions.

Chemical behavior in the boron group is driven by electron configuration. Each element has a specific number of electrons per shell. For example, boron has 2 electrons in its first shell and 3 in its second. As you move down the group, the number of electrons increases significantly. Aluminium has 13 electrons, while thallium has 113. This structure leads to important trends in physical properties. As you move from boron to thallium, the boiling points of the elements decrease. Meanwhile, the density of the elements tends to rise. Boron has a density of 2.46 g/cm³, but thallium is much denser at 11.85 g/cm³.

While the group shares many traits, the members are quite different in their physical states. Boron is a metalloid, meaning it has properties of both metals and non-metals. It is an insulator of heat and electricity at room temperature. However, it becomes a good conductor when it is heated. Boron is also incredibly hard, second only to diamond. Most other group members are metals and conduct electricity under normal conditions. These metals are generally soft, unlike the very hard boron. Boron also has an extremely high melting point of 2076 °C. This is much higher than aluminium, which melts at 660 °C.

Reactivity also follows specific patterns within the group. Most elements show increasing reactivity as they get heavier in atomic mass. Boron is generally unreactive at most temperatures, but it can form compounds called boranes when it reacts with hydrogen. The simplest borane is diborane, which has the formula B2H6. As you move down the group, the ability to form stable hydrides changes. Aluminium and gallium can form AlH3 and GaH3. However, indium does not form many hydrides, and thallium has no known stable hydrogen compounds synthesized in a laboratory.

Oxidation states, which describe the charge an atom takes in a compound, also change predictably. This is due to the inert s-pair effect, which is especially strong in heavier elements like thallium. In lighter elements, the +3 oxidation state is the most stable. As the atomic number increases, the +1 state becomes more common. For thallium, the +1 state is actually the most stable. All elements in the group can also form oxides by bonding with oxygen. These oxides show a trend in pH. Boron oxide is slightly acidic, while thallium oxide acts as a Lewis base, meaning it dissolves in acids to form salts.

History shows that discovering these elements required great scientific effort. Boron was known to ancient Egyptians as the mineral borax. In 1808, Humphry Davy used electrolysis to extract pure boron. He originally called it boracium. Aluminium was also known in minerals before it was extracted from alum. Hans Christian Ørsted prepared an impure form of aluminium in 1825. Later, Henri Etienne Deville produced the first pure sample. Today, we use a method developed by Charles Martin Hall and Paul Héroult. This method involves the electrolysis of aluminium oxide dissolved in cryolite.

These elements play very different roles in the world and in biology. Boron is a trace element in humans and is essential for some plants. However, too much or too little boron can inhibit plant growth. Aluminium has no biological role and is considered safe. Gallium is used in technology, such as in blue LEDs.

Indium is often found in minerals like sphalerite.

Thallium is highly toxic because it interferes with vital enzymes. Because of this toxicity, it was once used as a pesticide. Finally, nihonium is a synthetic element that is highly radioactive and must be created artificially.