Fluorine
Fluorine (F) is a reactive nonmetal with atomic number 9 and an atomic mass of 18.998. Its electron configuration is [He] 2s2 2p5, which gives it 7 valence electrons.
Fluorine key data
| Symbol | F |
|---|---|
| Atomic number | 9 |
| Atomic mass (standard atomic weight) | 18.998 |
| Molar mass | 18.998 g/mol |
| Protons | 9 |
| Neutrons (most abundant isotope, fluorine-19) | 10 |
| Electrons (neutral atom) | 9 |
| Valence electrons | 7 |
| Category | Reactive nonmetal |
| Period | 2 |
| Group | 17 |
| Block | p-block |
| Noble gas notation | [He] 2s2 2p5 |
| Full electron configuration | 1s2 2s2 2p5 |
| Electrons per shell | 2, 7 |
Atomic mass: IUPAC CIAAW abridged standard atomic weights, 2024. Most abundant isotope: NIST Atomic Weights and Isotopic Compositions.
The values are facts and free to use; this page’s selection and presentation are © 2026 ScienceQuest.
Measured properties of fluorine
From PubChem, the US National Institutes of Health. Public domain. The discovery year is the year fluorine was first isolated, from Wikipedia’s timeline of chemical element discoveries, in place of PubChem’s 1670. The electron affinity is the measured value for fluorine, from Wikipedia’s electron affinity data page, in place of PubChem’s 3.339 eV.
| Melting point | 53.53 K (−219.62 °C), 100th of 103 by melting point |
|---|---|
| Boiling point | 85.03 K (−188.12 °C), 89th of 93 by boiling point |
| Density | 0.001696 g/cm³, 91st of 96 by density |
| State at room temperature | Gas |
| Electronegativity | 3.98 (Pauling), 1st of 95 by electronegativity |
| Van der Waals radius | 135 pm, 98th of 99 by atomic radius |
| First ionisation energy | 17.423 eV (1681.1 kJ/mol), 3rd of 102 by first ionisation energy |
| Electron affinity | 3.40119 eV (328.165 kJ/mol), 2nd of 57 by electron affinity |
| Common oxidation states | −1 |
| Discovered | 1886 |
Each rank counts down from the highest value, among the elements PubChem’s table gives one for, and links to that property ranked across the whole table. All of them are collected under periodic trends.
Fluorine electron configuration
The full electron configuration of fluorine is 1s2 2s2 2p5. With the noble-gas core collapsed it is [He] 2s2 2p5, and the outermost subshell is 2p5.
Why group and block follow from this is set out in how the periodic table maps electron configuration, and the electron configuration of every element is listed on one page.
Mass of one fluorine atom
A molar mass is grams per mole, so dividing by the Avogadro constant gives the mass of a single atom, or for an element with more than one natural isotope the average mass of its atoms, and the reciprocal gives how many atoms sit in a gram.
Mass of one atom
- one atom = 18.998 / (6.02214076 × 10²³)
- = 3.1547 × 10⁻²³ g
Atoms in one gram
- atoms per gram = 6.02214076 × 10²³ / 18.998
- = 3.1699 × 10²² atoms
Fluorine on the periodic table
Fluorine is in period 2, group 17, in the p-block.
The other elements of group 17 are chlorine, bromine, iodine, astatine and tennessine.