Element 38 · Strontium (Sr)

Strontium Bohr model: diagram and electrons per shell

The strontium Bohr model shows a strontium atom (Sr) as a small nucleus with its electrons circling it in 5 shells: 2 in shell K, 8 in shell L, 18 in shell M, 8 in shell N and 2 in shell O. This page has a rotating 3D strontium Bohr model, a flat diagram, a table of the electrons in each shell and the steps to draw it yourself.

Rotate the strontium Bohr model in 3D

Drag to orbit, scroll to zoom.

This is a Bohr model of strontium (Sr), a simplified picture of a single strontium atom. Its nucleus holds 38 protons, and a neutral strontium atom has 38 electrons, arranged around it in 5 shells (2 in shell K, 8 in shell L, 18 in shell M, 8 in shell N and 2 in shell O).

Sr K · 21s² L · 82s² 2p⁶ M · 183s² 3p⁶ 3d¹⁰ N · 84s² 4p⁶ O · 25s²

Strontium Bohr model diagram

Bohr model diagram of strontium: a nucleus of 38 protons with 38 electrons on 5 shells, 2 in shell K, 8 in shell L, 18 in shell M, 8 in shell N and 2 in shell O, each ring labelled with its shell letter. — The strontium 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, 8 in shell N and 2 in shell O).

Strontium electrons per shell

A neutral strontium atom has 38 electrons, one for each of its 38 protons. They fill the shells from the nucleus outwards: 2 in shell K, 8 in shell L, 18 in shell M, 8 in shell N and 2 in shell O.

Electrons in each shell of the strontium 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	8	32	4s² 4p⁶
O	5	2	50	5s²

How the strontium Bohr model builds up, shell by shell

Watch the strontium 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, 8 in shell N and 2 in shell O) as it forms.

Animation of the strontium Bohr model being built: a nucleus of 38 protons appears first, then each shell grows in around it and takes its electrons, giving 38 electrons on 5 shells (2 in shell K, 8 in shell L, 18 in shell M, 8 in shell N and 2 in shell O). — The strontium 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, 8 in shell N and 2 in shell O. Protons are red, neutrons yellow and electrons blue.

How to draw the strontium Bohr model

Find the atomic number. Strontium has atomic number 38, so a neutral atom has 38 protons and 38 electrons.
Draw the nucleus. Put a circle in the centre and write Sr in it. The 38 protons sit there with the neutrons.
Draw the shells. Sketch 5 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, 8 in shell N and 2 in shell O.
Check the total. 2 + 8 + 18 + 8 + 2 = 38, the atomic number, so every electron is accounted for.

Atomic data for the strontium Bohr model

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

Identity

Symbol: Sr
Atomic number: 38
Atomic mass: 87.621 u
Family: Alkaline Earth Metals
Position: group 2, period 5
Block: s-block

Electron configuration

Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s²
Shorthand: [Kr] 5s²
Electrons per shell: 2, 8, 18, 8, 2
Outer-shell electrons: 2 in shell O

Ionisation energies

I₁: 549.5
I₂: 1064.2
I₃: 4138
I₄: 5500
I₅: 6910
I₆: 8760
I₇: 10230
I₈: 11800

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): 219
Empirical (pm): 200
Covalent (pm): 185
Van der Waals (pm): 249

Electronegativity and electron affinity

Electronegativity (Pauling): 0.95
Electron affinity (kJ/mol): 5.023

Oxidation states

Charges the element commonly takes in compounds.

Physical properties, abundance and history of strontium

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

Physical properties

Phase at room conditions: Solid
Melting point: 776.85°C (1050 K)
Boiling point: 1376.85°C (1650 K)
Density: 2.64 g/cm³
Specific heat (J/g·K): 0.306
Molar heat capacity (J/mol·K): 26.4
Heat of fusion (kJ/mol): 9.2
Heat of vaporisation (kJ/mol): 144

Abundance

Earth's crust (mg/kg): 370
Oceans (mg/L): 7.9

Discovery

Discovered by: William Cruickshank (chemist)
Year: 1790

Common compounds

Strontium Chromate CrO4Sr
Strontium carbonate CO3Sr
Strontium Sr
Strontium-90 Sr
Strontium nitrate N2O6Sr
Strontium bromide Br2Sr
Strontium Chloride Cl2Sr
Strontium dichloride hexahydrate Cl2H12O6Sr

Compounds listed in the PubChem database.

Main isotopes of strontium

Isotopes of strontium share the same 38 protons but differ in neutrons. Natural isotopes come first, then the longest-lived others.

Main isotopes of strontium: mass number, abundance, half-life and decay
Mass number	Natural abundance	Half-life	Decay
84	0.56 %	stable	2β⁺
85	–	64.846 d	EC
86	9.86 %	stable	–
87	7 %	stable	–
88	82.58 %	stable	–
90	–	28.91 y	β⁻

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

More about strontium

Strontium on the periodic table – properties, isotopes, uses and the full strontium page.
Alkaline Earth Metals – all alkaline earth metal elements and their trends.
Bohr model of every element – the Bohr model of all 118 elements.