Element 34 · Selenium (Se)

Selenium Bohr model: diagram and electrons per shell

The selenium Bohr model shows a selenium atom (Se) as a small nucleus with its electrons circling it in 4 shells: 2 in shell K, 8 in shell L, 18 in shell M and 6 in shell N. This page has a rotating 3D selenium Bohr model, a flat diagram, a table of the electrons in each shell and the steps to draw it yourself.

Rotate the selenium Bohr model in 3D

Drag to orbit, scroll to zoom.

This is a Bohr model of selenium (Se), a simplified picture of a single selenium atom. Its nucleus holds 34 protons, and a neutral selenium atom has 34 electrons, arranged around it in 4 shells (2 in shell K, 8 in shell L, 18 in shell M and 6 in shell N).

Se K · 21s² L · 82s² 2p⁶ M · 183s² 3p⁶ 3d¹⁰ N · 64s² 4p⁴

Selenium Bohr model diagram

Bohr model diagram of selenium: a nucleus of 34 protons with 34 electrons on 4 shells, 2 in shell K, 8 in shell L, 18 in shell M and 6 in shell N, each ring labelled with its shell letter. — The selenium Bohr model drawn flat: each ring is a shell, labelled with its letter, and every dot is an electron (2 in shell K, 8 in shell L, 18 in shell M and 6 in shell N).

Selenium electrons per shell

A neutral selenium atom has 34 electrons, one for each of its 34 protons. They fill the shells from the nucleus outwards: 2 in shell K, 8 in shell L, 18 in shell M and 6 in shell N.

Electrons in each shell of the selenium Bohr model
Shell	Shell number (n)	Electrons	Most it can hold (2n²)	Subshells
K	1	2	2	1s²
L	2	8	8	2s² 2p⁶
M	3	18	18	3s² 3p⁶ 3d¹⁰
N	4	6	32	4s² 4p⁴

How the selenium Bohr model builds up, shell by shell

Watch the selenium 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, 8 in shell L, 18 in shell M and 6 in shell N) as it forms.

Animation of the selenium Bohr model being built: a nucleus of 34 protons appears first, then each shell grows in around it and takes its electrons, giving 34 electrons on 4 shells (2 in shell K, 8 in shell L, 18 in shell M and 6 in shell N). — The selenium Bohr model built up in six seconds: the nucleus first, then each shell with its electrons, ending with 2 in shell K, 8 in shell L, 18 in shell M and 6 in shell N. Protons are red, neutrons yellow and electrons blue.

How to draw the selenium Bohr model

Find the atomic number. Selenium has atomic number 34, so a neutral atom has 34 protons and 34 electrons.
Draw the nucleus. Put a circle in the centre and write Se in it. The 34 protons sit there with the neutrons.
Draw the shells. Sketch 4 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.
Place the electrons. Fill from the inside out: 2 in shell K, 8 in shell L, 18 in shell M and 6 in shell N.
Check the total. 2 + 8 + 18 + 6 = 34, the atomic number, so every electron is accounted for.

Atomic data for the selenium Bohr model

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

Identity

Symbol: Se
Atomic number: 34
Atomic mass: 78.9718 u
Family: Reactive Nonmetals
Position: group 16, period 4
Block: p-block

Electron configuration

Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁴
Shorthand: [Ar] 3d¹⁰ 4s² 4p⁴
Electrons per shell: 2, 8, 18, 6
Outer-shell electrons: 6 in shell N

Ionisation energies

I₁: 941
I₂: 2045
I₃: 2973.7
I₄: 4144
I₅: 6590
I₆: 7880
I₇: 14990

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): 103
Empirical (pm): 115
Covalent (pm): 116
Van der Waals (pm): 190

Electronegativity and electron affinity

Electronegativity (Pauling): 2.55
Electron affinity (kJ/mol): 194.959

Oxidation states

−2 +2 +4 +6

Charges the element commonly takes in compounds.

Physical properties, abundance and history of selenium

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

Physical properties

Phase at room conditions: Solid
Appearance: Black, red, and gray (not pictured) allotropes
Melting point: 220.85°C (494 K)
Boiling point: 684.85°C (958 K)
Density: 4.81 g/cm³
Thermal conductivity (W/m·K): 0.52
Specific heat (J/g·K): 0.321
Molar heat capacity (J/mol·K): 25.363
Heat of fusion (kJ/mol): 5.23
Heat of vaporisation (kJ/mol): 59.7

Abundance

Earth's crust (mg/kg): 0.05
Oceans (mg/L): 0

Discovery

Discovered by: Jöns Jakob Berzelius
Year: 1817

Common compounds

Selenious Acid H2O3Se
DL-selenomethionine C5H11NO2Se
Methylselenocysteine C4H9NO2Se
Selenium Se
L-Selenomethionine C5H11NO2Se
Sodium Selenite Na2O3Se
Ebselen C13H9NOSe
Selenium Dioxide O2Se

Compounds listed in the PubChem database.

Main isotopes of selenium

Isotopes of selenium share the same 34 protons but differ in neutrons. Natural isotopes come first, then the longest-lived others.

Main isotopes of selenium: mass number, abundance, half-life and decay
Mass number	Natural abundance	Half-life	Decay
74	0.86 %	stable	2β⁺
76	9.23 %	stable	–
77	7.6 %	stable	–
78	23.69 %	stable	–
80	49.8 %	stable	2β⁻
82	8.82 %	87.6 Ey	2β⁻

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

More about selenium

Selenium on the periodic table – properties, isotopes, uses and the full selenium page.
Reactive Nonmetals – all reactive nonmetal elements and their trends.
Bohr model of every element – the Bohr model of all 118 elements.