Strontium (Sr)
Strontium is element 38, an alkaline earth metal in group 2, period 5. A neutral atom has 38 protons, 50 neutrons and 38 electrons, 2 of them valence electrons.
Alkaline earth metal- Atomic number
- 38
- Atomic mass
- 87.62 u
- Valence electrons
- 2
- Protons · neutrons
- 38 · 50
- Electrons per shell
- 2, 8, 18, 8, 2
- At room temperature
- solid
Bohr model of strontium
The Bohr model draws strontium as a nucleus of 38 protons and 50 neutrons, with its 38 electrons on 5 circular shells: 2 in shell 1, 8 in shell 2, 18 in shell 3, 8 in shell 4, 2 in shell 5. Press Build the atom to watch the shells fill from the inside out. The outer ring (the O shell) is dashed: the electrons there are the ones that take part in chemistry.
Real electrons don't travel in neat circles. They live in fuzzy orbitals, shown below, but the Bohr picture is the quickest way to count shells and valence electrons.
Electron configuration of strontium
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s²
Short form (noble gas notation): [Kr] 5s². The [Kr] stands for the electrons of krypton, the noble gas before it.
How many valence electrons does strontium have?
Strontium has 2 valence electrons.
Strontium is in group 2, so it has 2 valence electrons. It tends to lose them and form a +2 ion.
Protons, neutrons and electrons
| Protons | 38 | equal to the atomic number |
|---|---|---|
| Electrons | 38 | equal to the protons in a neutral atom |
| Neutrons | 50 | mass number 88 − 38 protons |
Atoms of the same element can have different numbers of neutrons (isotopes). The count above uses the rounded atomic mass, the way it's taught in class.
Strontium properties
| Symbol | Sr |
|---|---|
| Category | Alkaline earth metal |
| Group · period · block | 2 · 5 · s |
| Atomic mass | 87.62 u |
| State at 25 °C | solid |
| Melting point | 1,050 K (777 °C, 1,430 °F) |
| Boiling point | 1,655 K (1,380 °C, 2,520 °F) |
| Density | 2.64 g/cm³ |
| Electronegativity (Pauling) | 0.95 |
| Atomic radius | 249 pm |
| First ionization energy | 5.695 eV |
| Electron affinity | — |
| Oxidation states | +2 |
| Common ion charge | +2 |
| Discovered | 1790 by William Cruickshank (chemist) |
Where strontium sits on the periodic table
Group 2: Beryllium, Magnesium, Calcium, Barium, Radium.
Questions about strontium
How many valence electrons does strontium have?
Strontium has 2 valence electrons.
How many protons, neutrons and electrons does strontium have?
A neutral strontium atom has 38 protons and 38 electrons. Its most common form has about 50 neutrons (mass number 88 − 38 protons).
What is the electron configuration of strontium?
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s², written in short form as [Kr] 5s².
What does the Bohr model of strontium look like?
A nucleus of 38 protons and 50 neutrons, circled by 5 electron shells holding 2, 8, 18, 8, 2 electrons.
What is the atomic number of strontium?
38. The atomic number is the number of protons in the nucleus, and it is what makes an atom strontium.