Strontium (Sr)

Element 38 · alkaline earth metal · group 2, period 5

Electron shells, 2 + 8 + 18 + 8 + 2. The outer shell is highlighted - it is the only one that takes part in bonding.

Strontium is element 38, a alkaline earth metal in group 2 and period 5. Its electron configuration is [Kr] 5s2. That leaves 2 valence electrons in the outer shell, with the shells filling 2, 8, 18, 8, 2. Losing its 2 valence electrons is the shorter route to a full shell, so it carries a charge of +2.

38 protons
2 valence e−
+2
s-block

Properties

Atomic number	38
Symbol	Sr
Standard atomic weight	87.62 u
Group	2
Period	5
Block	s-block
Category	alkaline earth metal
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 5s²
Noble-gas notation	[Kr] 5s²
Electrons per shell	2, 8, 18, 8, 2
Valence electrons	2
Common ionic charge	+2
Electronegativity (Pauling)	0.95
Protons / electrons	38 / 38

Electron configuration of strontium

Orbitals fill from the lowest energy upward. Writing that out for strontium gives 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 5s², which is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 5s2 in plain text.

Everything up to Kr is the same as in that noble gas, so it is usually abbreviated to [Kr] 5s². The part outside the bracket is what does the chemistry.

Subshell	Electrons	Capacity
1s	2	2
2s	2	2
2p	6	6
3s	2	2
3p	6	6
3d	10	10
4s	2	2
4p	6	6
5s	2	2

Strontium ion charge

Strontium commonly forms ions with a charge of +2.

It has 2 valence electrons, so it is 6 short of a full octet and 2 above an empty outer shell. An atom takes whichever route is shorter, which is why the charge comes out as it does.

Common questions

How many valence electrons does strontium have?

Strontium has 2 valence electrons. For groups 1 and 2 the count is the group number, and strontium is in group 2.

What is the electron configuration of strontium?

1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 5s2, or [Kr] 5s2 written from the previous noble gas. Orbitals fill lowest energy first.

What is the charge of strontium?

Strontium commonly forms ions with a charge of +2. With 2 valence electrons it is 6 short of an octet and 2 above an empty shell, so it takes whichever route is shorter.

How many protons, electrons and neutrons does strontium have?

A neutral strontium atom has 38 protons and 38 electrons. Its standard atomic weight is 87.62, so the most common isotope has about 50 neutrons.

See the ionic charge of every element →

How this page was produced. The configuration was built by filling orbitals in energy order from atomic number 38 alone, not looked up. The shell counts, the valence count and the charge all follow from it. Nothing on this page is written per element.