Selenium (Se)
Selenium's name comes from Selene, the Greek goddess of the Moon.
Selenium properties
- Atomic mass
- 78.971 u
- Category
- Reactive nonmetal
- Group
- 16
- Period
- 4
- Block
- p-block
- State at room temp.
- Solid
- Electronegativity
- 2.55
- Melting point
- 494 K (220.9 °C)
- Boiling point
- 958 K (684.8 °C)
- Density
- 4.81 g/cm³
- Oxidation states
- +6, +4, −2
- Atomic radius
- 190 pm
- Ionization energy
- 9.752 eV
- Electron affinity
- 2.021 eV
- Radioactive
- No, has stable isotopes
- Discovered
- 1817
Selenium electron configuration
- Electron configuration
- [Ar] 3d10 4s2 4p4
- Full electron configuration
- 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p4
- Electron shells
- 2 · 8 · 18 · 6
The electron configuration of Selenium (Se) is [Ar] 3d10 4s2 4p4. Its 34 electrons are arranged in shells as 2, 8, 18, 6.
Protons, neutrons and electrons in Selenium
A neutral Selenium atom has 34 protons and 34 electrons. Most Selenium atoms have about 45 neutrons: the atomic mass rounded to 79, minus the atomic number 34.
Neutrons are approximate: atoms of the same element can have different numbers of neutrons (isotopes). Atomic number and mass
How many valence electrons does Selenium have?
6
Selenium has 6 valence electrons in its outermost shell, shell 4. These are the electrons involved in chemical bonding.
Selenium orbital diagram
Each box is an orbital that holds up to two electrons with opposite spins (↑↓). The inner shells are the same as the noble gas in brackets. How to write electron configurations
Molar mass of Selenium
78.971 g/mol
One mole of Selenium atoms (6.022 × 10²³ atoms) has a mass of 78.971 grams. Use this value to convert between grams and moles.
Selenium facts
- Selenium's name comes from Selene, the Greek goddess of the Moon.
- Its electrical conductivity rises in light, which made it key to early photocopiers and light meters.
- Selenium (Se) has atomic number 34 and is a solid at room temperature. It was discovered in 1817.
Position in the periodic table
Selenium is element 34, in period 4 and group 16 of the periodic table, in the p-block.
Uses of Selenium
Selenium is used in glassmaking, both to cancel out the green tint caused by iron impurities and to give glass a red color. It is added to fertilizers and animal feed in regions with selenium-poor soils, and selenium sulfide is the active ingredient in some anti-dandruff shampoos. Selenium compounds are also used in some thin-film solar cells.
Who discovered Selenium?
Swedish chemists Jöns Jacob Berzelius and Johan Gottlieb Gahn discovered selenium in 1817 in a reddish sludge from a sulfuric acid works at Gripsholm, Sweden. Berzelius at first mistook it for tellurium.
Where does the name come from?
Selenium comes from the Greek selene, meaning 'Moon'. Jöns Jacob Berzelius named it in 1817 because it closely resembled tellurium, which had been named after the Earth (Latin tellus).
Same group
Compare Selenium
FAQ
What is the electron configuration of Selenium?
The electron configuration of Selenium (Se) is [Ar] 3d10 4s2 4p4. Its 34 electrons are arranged in shells as 2, 8, 18, 6.
How many protons, neutrons and electrons does Selenium have?
A neutral Selenium atom has 34 protons and 34 electrons. Most Selenium atoms have about 45 neutrons: the atomic mass rounded to 79, minus the atomic number 34.
How many valence electrons does Selenium have?
Selenium has 6 valence electrons in its outermost shell, shell 4. These are the electrons involved in chemical bonding.
What is the molar mass of Selenium?
The molar mass of Selenium is 78.971 g/mol. This is the same number as its atomic mass, 78.971 u.
Is Selenium a metal?
No. Selenium is a reactive nonmetal, so it is a nonmetal.
Is Selenium radioactive?
Ordinary Selenium is not radioactive: it has at least one stable isotope. Like every element, it also has radioactive isotopes, most of them made in laboratories.
Where is Selenium on the periodic table?
Selenium is element 34, in period 4 and group 16 of the periodic table, in the p-block.