Selenium (Se)
Element 34 · reactive nonmetal · group 16, period 4
Selenium is element 34, a reactive nonmetal in group 16 and period 4. Its electron configuration is [Ar] 3d10 4s2 4p4. That leaves 6 valence electrons in the outer shell, with the shells filling 2, 8, 18, 6. It is 2 electrons short of a full octet, so it gains them and carries a charge of -2, +4, +6.
- 34 protons
- 6 valence e−
- -2, +4, +6
- p-block
Selenium Lewis dot structure
Selenium has 6 valence electrons, so its Lewis symbol carries 6 dots: two pairs and 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.
Draw it in the Lewis structure generator →
Properties
| Atomic number | 34 |
|---|---|
| Symbol | Se |
| Standard atomic weight | 78.971 u |
| Group | 16 |
| Period | 4 |
| Block | p-block |
| Category | reactive nonmetal |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p4 |
| Noble-gas notation | [Ar] 3d10 4s2 4p4 |
| Electrons per shell | 2, 8, 18, 6 |
| Valence electrons | 6 |
| Common ionic charge | -2, +4, +6 |
| Electronegativity (Pauling) | 2.55 |
| Protons / electrons | 34 / 34 |
Electron configuration of selenium
Orbitals fill from the lowest energy upward. Writing that out for selenium gives 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p4, which is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p4 in plain text.
Everything up to Ar is the same as in that noble gas, so it is usually abbreviated to [Ar] 3d10 4s2 4p4. 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 | 4 | 6 |
Selenium ion charge
Selenium commonly forms ions with a charge of -2, +4, +6.
It has 6 valence electrons, so it is 2 short of a full octet and 6 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 selenium?
The symbol Se with 6 dots, one for each valence electron: two pairs and two single dots. Dots go one to a side before any pair up, the same way electrons fill separate orbitals before sharing one.
How many valence electrons does selenium have?
Selenium has 6 valence electrons. For a main-group element the count is the group number minus 10, and selenium is in group 16.
What is the electron configuration of selenium?
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p4, or [Ar] 3d10 4s2 4p4 written from the previous noble gas. Orbitals fill lowest energy first.
What is the charge of selenium?
Selenium commonly forms ions with a charge of -2, +4, +6. With 6 valence electrons it is 2 short of an octet and 6 above an empty shell, so it takes whichever route is shorter.
How many protons, electrons and neutrons does selenium have?
A neutral selenium atom has 34 protons and 34 electrons. Its standard atomic weight is 78.971, so the most common isotope has about 45 neutrons.
Selenium in Lewis structures
What the configuration above means in practice. Selenium brings 6 valence electrons to each of these, and the working on every one of them starts by counting exactly that.
Nearby elements
See the ionic charge of every element →