Boron (B)

Boron properties

Atomic number

5

Atomic mass

10.81 u

Category

Metalloid

Group

13

Period

2

Block

p-block

State at room temp.

Solid

Electronegativity

2.04

Melting point

2,349 K (2,075.8 °C)

Boiling point

4,200 K (3,926.8 °C)

Density

2.34 g/cm³

Valence electrons

3

Common charges

+3

Oxidation states

+3

Atomic radius

192 pm

Ionization energy

8.298 eV

Electron affinity

0.277 eV

Radioactive

No, has stable isotopes

Discovered

1808

Boron electron configuration

The electron configuration of Boron (B) is [He] 2s2 2p1. Its 5 electrons are arranged in shells as 2, 3.

Protons, neutrons and electrons in Boron

A neutral Boron atom has 5 protons and 5 electrons. Most Boron atoms have about 6 neutrons: the atomic mass rounded to 11, minus the atomic number 5.

Neutrons are approximate: atoms of the same element can have different numbers of neutrons (isotopes). Atomic number and mass

How many valence electrons does Boron have?

3

Boron has 3 valence electrons in its outermost shell, shell 2. These are the electrons involved in chemical bonding.

See every element: Periodic table with valence electrons

Boron orbital diagram

Each box is an orbital that holds up to two electrons with opposite spins (↑↓). The inner shells are the same as the noble gas in brackets. How to write electron configurations

Molar mass of Boron

10.81 g/mol

One mole of Boron atoms (6.022 × 10²³ atoms) has a mass of 10.81 grams. Use this value to convert between grams and moles.

Compounds containing Boron

Boron facts

• Most of the boron in the universe was made not inside stars but by cosmic rays smashing into carbon and oxygen atoms in space.
• Plants need small amounts of boron to build strong cell walls, so boron is added to some fertilizers.
• Boron (B) has atomic number 5 and is a solid at room temperature. It was discovered in 1808.

Position in the periodic table

Boron is element 5, in period 2 and group 13 of the periodic table, in the p-block.

All metalloids

Uses of Boron

Boron, mostly in the form of borates, is used to make fiberglass insulation and borosilicate glass, the heat-resistant glass in laboratory glassware and ovenware. Borax is found in detergents and cleaning products, and very hard boron carbide is used in body armor and tank armor. Boron is also a key ingredient of powerful neodymium magnets, and boron-10 absorbs neutrons in nuclear reactor control systems.

Who discovered Boron?

Boron was first isolated, in impure form, in 1808 by the French chemists Joseph Louis Gay-Lussac and Louis Jacques Thénard and, independently, by Humphry Davy in London, all working from boric acid. Very pure boron was not produced until the early 20th century.

Where does the name come from?

Boron is named after borax, a boron-rich mineral, with an ending borrowed from carbon, an element it resembles. Borax reached English through Medieval Latin from the Arabic buraq, which in turn comes from Persian.

Discovery timeline