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Name Boron
Atomic Number 5
Atomic Weight 10.811
Symbol B
Melting Point ( °C ) 2300
Boiling Point ( °C ) 2550
Density (g/cm3) 2.34
Earth crust (%)
Discovery (Year) 1808
Group 13
Electron configuration [He] 2s2 2p1
Ionization energy (eV) 8.298

Boron is the 1st element of group 13 on the periodic table with an atomic number of 5. Boron is also the first metalloid (semi-metal) of the periodic table. CITATION REQUIRED


The first mention of boron compounds is found in a book by Persian alchemist Rhazes (c. 865-c. 925). CITATION REQUIRED Alchemists studied the nature of matter before modern chemistry was born. Rhazes classified minerals into six classes, one of which was the boraces, which included borax.

Borax was widely used by crafts people. CITATION REQUIRED It reduces the melting point of materials used to make glass. It was also used to melt the ores of metals and to isolate the metals from those ores.

In 1808, English chemist Humphry Davy (1778-1829) had just learned how to isolate the most active metals, such as sodium and potassium. CITATION REQUIRED He was also working on a method to remove boron from its compounds. (See sidebar on Davy in the calcium entry.)

News of Davy's success had traveled to France, where emperor Napoleon Bonaparte (1769-1821) grew concerned about the scientific reputation of his country. CITATION REQUIRED He ordered larger and better equipment built for his scientists. He wanted them to surpass Davy in his work on metals. This equipment was designed especially for two French chemists, Louis Jacques Thênard (1777-1857) and Joseph Louis Gay-Lussac (1778-1850).

Thênard and Gay-Lussac found a new way to separate boron from its compounds. They heated boracic acid (also known as boric acid, H3BO3) with potassium metal to produce impure boron. Thênard and Gay-Lussac were given credit for discovering the new element. In 1892, French chemist Henri Moissan (1852-1907) produced boron that was 98 percent pure.

The names borax and boracic acid probably originated as far back as the time of Rhazes as buraq (in Arabic) or burah (in Persian). CITATION REQUIRED

Atomic Structure


Chemical Properties

Boron combines with oxygen in the air to form boron trioxide (B2O3). Boron trioxide forms a thin film on the surface that prevents further reaction with oxygen.

Boron is not soluble in water. It normally does not react with acids. In powder form, it reacts with hot nitric acid (HNO3) and hot sulfuric acid (H2SO4). It also dissolves in molten (melted) metals.

Physical Properties

One of the unusual properties of boron is the many physical forms, called allotropes, in which it occurs. CITATION REQUIRED Allotropes are forms of an element with different physical and chemical properties. One form of boron consists of clear red crystals with a density of 2.46 grams per cubic centimeter. A second form consists of black crystals with a metallic appearance and a density of 2.31 grams per cubic centimeter. Boron can also occur as a brown powder with no crystalline structure. The density of this powder is 2.350 grams per cubic centimeter.

All forms of boron have very high melting points, from 2,200 to 2,300°C (4,000 to 4,200°F). CITATION REQUIRED

One property of special importance is boron's ability to absorb neutrons. Neutrons are subatomic particles with no charge that occur in the nucleus of nearly all atoms. Boron atoms are able to absorb a large number of neutrons. This makes boron useful in the control rods of nuclear reactors.

Boron an element found in grains,nuts,leafy greens

Incorrect content

A nuclear reactor is a device for generating energy from nuclear fission reactions. Nuclear fission is the process in which large atoms are split, releasing large amounts of energy and smaller atoms. In a nuclear reactor, it is essential that just the right number of neutrons are present. Too many neutrons can cause a fission reaction to get out of control. Too few neutrons and a fission reaction stops.

Control rods are long tubes packed with boron (or some other element). The rods can be raised and lowered in the reactor. As the rods are lowered into the core, the boron absorbs neutrons, slowing the reaction.

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