Strontium (Sr)
Element 38 · alkaline earth metal · group 2, period 5
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
Strontium Lewis dot structure
Strontium has 2 valence electrons, so its Lewis symbol carries 2 dots: two single dots. The dots go one to a side before any of them pair up, so the unpaired ones show exactly how many bonds the atom tends to form. The ion has given those electrons away, which is why it is drawn in brackets with none.
Draw it in the Lewis structure generator →
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
What is the Lewis dot structure of strontium?
The symbol Sr with 2 dots, one for each valence electron: two single dots. Dots go one to a side before any pair up, the same way electrons fill separate orbitals before sharing one. The Sr2+ ion is drawn in brackets with no dots, because it has lost them.
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.
Nearby elements
See the ionic charge of every element →