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Element 5 · Boron (B)

Boron Bohr model: diagram and electrons per shell

The boron Bohr model shows a boron atom (B) as a small nucleus with its electrons circling it in 2 shells: 2 in shell K and 3 in shell L. This page has a rotating 3D boron Bohr model, a flat diagram, a table of the electrons in each shell and the steps to draw it yourself.

Rotate the boron Bohr model in 3D

Drag to orbit, scroll to zoom.

This is a Bohr model of boron (B), a simplified picture of a single boron atom. Its nucleus holds 5 protons, and a neutral boron atom has 5 electrons, arranged around it in 2 shells (2 in shell K and 3 in shell L).

B K · 21s2 L · 32s2 2p1

Boron Bohr model diagram

Bohr model diagram of boron: a nucleus of 5 protons with 5 electrons on 2 shells, 2 in shell K and 3 in shell L, each ring labelled with its shell letter.
The boron Bohr model drawn flat: each ring is a shell, labelled with its letter, and every dot is an electron (2 in shell K and 3 in shell L).

Boron electrons per shell

A neutral boron atom has 5 electrons, one for each of its 5 protons. They fill the shells from the nucleus outwards: 2 in shell K and 3 in shell L.

Electrons in each shell of the boron Bohr model
ShellShell number (n)ElectronsMost it can hold (2n²)Subshells
K1221s2
L2382s2 2p1

How the boron Bohr model builds up, shell by shell

Watch the boron Bohr model come together: the nucleus first, then each shell in turn, from the innermost outwards, with its electrons joining the ring. The legend names every shell and counts its electrons, so you can read off the arrangement (2 in shell K and 3 in shell L) as it forms.

Animation of the boron Bohr model being built: a nucleus of 5 protons appears first, then each shell grows in around it and takes its electrons, giving 5 electrons on 2 shells (2 in shell K and 3 in shell L).
The boron Bohr model built up in six seconds: the nucleus first, then each shell with its electrons, ending with 2 in shell K and 3 in shell L. Protons are red, neutrons yellow and electrons blue.

How to draw the boron Bohr model

  1. Find the atomic number. Boron has atomic number 5, so a neutral atom has 5 protons and 5 electrons.
  2. Draw the nucleus. Put a circle in the centre and write B in it. The 5 protons sit there with the neutrons.
  3. Draw the shells. Sketch 2 shells as rings around the nucleus. A shell holds at most 2n² electrons: 2 in the first, 8 in the second, 18 in the third and 32 in the fourth.
  4. Place the electrons. Fill from the inside out: 2 in shell K and 3 in shell L.
  5. Check the total. 2 + 3 = 5, the atomic number, so every electron is accounted for.

Atomic data for the boron Bohr model

The numbers behind the boron Bohr model, grouped by topic. Radii are in picometres (pm) and energies in kilojoules per mole (kJ/mol).

Identity

Symbol
B
Atomic number
5
Atomic mass
10.81 u
Family
Metalloids
Position
group 13, period 2
Block
p-block

Electron configuration

Full
1s2 2s2 2p1
Shorthand
[He] 2s2 2p1
Electrons per shell
2, 3
Outer-shell electrons
3 in shell L

Ionisation energies

I₁
800.6
I₂
2427.1
I₃
3659.7
I₄
25025.8
I₅
32826.7

Energy to remove each electron in turn (kJ/mol). A sharp jump means the next electron comes from an inner shell.

Atomic radii

Calculated (pm)
87
Empirical (pm)
85
Covalent (pm)
85
Van der Waals (pm)
192

Electronegativity and electron affinity

Electronegativity (Pauling)
2.04
Electron affinity (kJ/mol)
26.989

Oxidation states

+3

Charges the element commonly takes in compounds.

Physical properties, abundance and history of boron

Bulk properties of boron, how common it is, who discovered it and some of its compounds.

Physical properties

Phase at room conditions
Solid
Appearance
Black-brown
Melting point
2075.85°C (2349 K)
Boiling point
3926.85°C (4200 K)
Density
2.08 g/cm³
Thermal conductivity (W/m·K)
27.4
Specific heat (J/g·K)
1.026
Molar heat capacity (J/mol·K)
11.087
Heat of fusion (kJ/mol)
23.6
Heat of vaporisation (kJ/mol)
504.5

Abundance

Earth's crust (mg/kg)
10
Oceans (mg/L)
4.44

Discovery

Discovered by
Joseph Louis Gay-Lussac
Year
1808

Common compounds

  • Boric Acid BH3O3
  • Bortezomib C19H25BN4O4
  • Crisaborole C14H10BNO3
  • Phenylboronic Acid C6H7BO2
  • Tavaborole C7H6BFO2
  • Ixazomib C14H19BCl2N2O4
  • Sodium Perborate BNaO3
  • Boron B

Compounds listed in the PubChem database.

Main isotopes of boron

Isotopes of boron share the same 5 protons but differ in neutrons. Natural isotopes come first, then the longest-lived others.

Main isotopes of boron: mass number, abundance, half-life and decay
Mass numberNatural abundanceHalf-lifeDecay
8–771.9 msβ⁺, β⁺α
1019.65 %stable–
1180.35 %stable–
12–20.2 msβ⁻, β⁻α
13–17.16 msβ⁻, β⁻n
14–12.36 msβ⁻, β⁻n, 2n

α = alpha decay, β⁻ = beta-minus, β⁺ = beta-plus, EC = electron capture, SF = spontaneous fission, p / n = proton / neutron emission.

More about boron