Boron (B)

Boron-10 has an enormous appetite for slow neutrons, absorbing them roughly 200,000 times more readily than most nuclei, which is why it lines reactor control rods and why boric acid is dumped into a reactor coolant loop in an emergency. Boron carbide is the third-hardest material in bulk production, behind diamond and cubic boron nitride. Almost all of the world's commercial boron comes from a handful of dried-up lake beds, mostly in Turkey and the Mojave Desert in California.

Properties

Atomic number

5

Symbol

B

Standard atomic weight

10.81 u

Category

Metalloid

Group

13

Period

2

Block

p-block

Electron configuration

[He] 2s² 2p¹

Electrons per shell

2, 3

Melting point

2,348 K — 2074.8 °C — 3766.7 °F

Boiling point

4,273 K — 3999.8 °C — 7231.7 °F

Density

2.37 g/cm³

Electronegativity

2.04 (Pauling)

Oxidation states

+3

Discovered

1808 by Joseph Louis Gay-Lussac, Louis Jacques Thénard and Humphry Davy

Electron configuration

Full

1s² 2s² 2p¹

Noble gas shorthand

[He] 2s² 2p¹

Shells

K: 2 · L: 3

What it is used for

• Borosilicate glass for laboratory ware and oven dishes
• Boron carbide in body armour and tank plating
• Control rods and shielding in nuclear reactors
• Borax in laundry detergent and as a metalworking flux
• A micronutrient in fertiliser — plants cannot set fruit without it

IUPAC publishes an interval, [10.806, 10.821]; 10.81 is the conventional value. The variation is real and useful — the boron-10 fraction differs enough between mineral deposits to fingerprint their origin.

Neighbours in the table

Group 13

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Boron sits in group 13 with aluminum, gallium, indium, thallium, nihonium.