Page 30 - Curriculum Visions Dynamic Book
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Boron (B)
Element 5. Boron is a metalloid
(with properties between a metal
and a non-metal) in group 3 in the Periodic Table. It is close to silicon
in its chemistry. For example, it is chemically inert and even resists strong acids. Because it is unreactive, it is difficult to isolate the element from its compounds. It is a very hard, black semiconductor.
Key facts...
Name: boron
Symbol: B
Atomic number: 5
Atomic weight: 10.81
Position in Periodic Table: group 3 (13) (boron
group); period 2
State at room temperature: solid
Colour: black
Density of solid: 2.34 g/cc
Melting point: 2,200°C
Boiling point: 2,550°C
Origin of name: from the Arabic word buraq,
meaning borax
Shell pattern of electrons: 2–3
Discovery
Boron compounds have been known since ancient times, but the element was only isolated in 1808 independently by Joseph- Louis Gay-Lussac and Louis-Jacques Thenard and also by Sir Humphry Davy. They did it by reacting boric acid with potassium.
Borosilicate glass bowl
Boron can increase hardness in steel. Borosilicate glass, the common heat-proof glass used for ovenware, is often found under the trade name Pyrex®. Borax is used as a flux in welding and as a water- softening agent in some washing powders. Boron compounds are used to make enamel. Boron produces a green colour
in fireworks.
Geology
Boron is not found as a native element. It commonly appears in the minerals borax (Na2B4O5(OH)4.8H2O) and in tourmaline.
Biology
Boron is needed by algae and plants.
It is probably not essential for animals. Boracic acid is an antiseptic, and in more concentrated form it is applied to control cockroaches and other insects.
Technology
It will scratch corundum (hardness 9 on Mohs’ scale of hardness) and so can be
used as an abrasive.
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