Fluorine (F): electron configuration, atomic mass and facts
Fluorine (F) is element 9 of the periodic table, a halogen in period 2, group 17. Its electron configuration is [He] 2s2 2p5, with electrons arranged in shells 2, 7, and its standard atomic weight is 18.998 u.
💡 The most electronegative element. Fluoride in toothpaste strengthens teeth.
▶ Watch Fluorine’s electrons orbit in the interactive periodic tableFluorine at a glance
| Symbol | F |
|---|---|
| Atomic number | 9 |
| Atomic mass | 18.998 u |
| Category | Halogen |
| Group | 17 |
| Period | 2 |
| Block | p-block |
| Electron configuration | 1s2 2s2 2p5 |
| Noble-gas shorthand | [He] 2s2 2p5 |
| Electrons per shell | 2, 7 |
| Outer-shell electrons | 7 |
| Electronegativity (Pauling) | 3.98 |
| State at 20 °C | gas |
Where is Fluorine on the periodic table?
Fluorine is in period 2, group 17, in the p-block. The period number matches its 2 electron shells, and the block names the subshell its last electrons fill. In the same group, Chlorine sits directly below it. Elements in one group have the same number of outer-shell electrons (7 here), which is why they react in similar ways.
How to work out the electron configuration of Fluorine
Put 9 electrons into subshells in order of rising energy, filling each before starting the next: 1s² (2), 2s² (4), 2p⁵ (9). In shorthand, [He] stands for the 2 electrons of helium, giving [He] 2s² 2p⁵.
How electronegative is Fluorine?
Fluorine has a Pauling electronegativity of 3.98, ranking 1 of the 100 elements with a known value (fluorine is highest at 3.98). That is high: it pulls shared electrons strongly towards itself in a bond.
Frequently asked questions
What is the electron configuration of Fluorine?
The electron configuration of Fluorine (F) is 1s2 2s2 2p5. In noble-gas shorthand it is written [He] 2s2 2p5.
How many electrons does Fluorine have in each shell?
Fluorine has 9 electrons arranged in shells as 2, 7. It has 7 electrons in its outer shell.
What is the atomic mass of Fluorine?
The standard atomic weight of Fluorine is 18.998 u, so one mole of Fluorine atoms has a mass of about 18.998 g.
Is Fluorine a metal?
No. Fluorine is a halogen.
Explore nearby elements
More halogens: Chlorine, Bromine, Iodine, Astatine, Tennessine. See all elements on the periodic table.