Chlorine vs Fluorine
Both are diatomic non-metals, so they share the same broad chemistry.
The differences in plain English
- They sit in the same column, group 17, so they have the same number of outer electrons and react in similar ways; the heavier one, Chlorine, is usually the more reactive of the two if they are metals, and the less reactive if they are non-metals.
- Both are gass at room temperature.
- Chlorine is denser, about 89 per cent more than Fluorine (3.2 against 1.696 g/L).
- Chlorine melts at -102 °C, Fluorine at -220 °C.
- An atom of Chlorine is about 87 per cent heavier than an atom of Fluorine (35.45 u against 19.00 u).
- Fluorine pulls electrons more strongly in a bond (electronegativity 3.98 against 3.16).
Side by side
| Chlorine | Fluorine | |
|---|---|---|
| Atomic number | 17 | 9 |
| Symbol | Cl | F |
| Family | Diatomic non-metal | Diatomic non-metal |
| Group / period | 17 / 3 | 17 / 2 |
| State at room temperature | Gas | Gas |
| Atomic mass | 35.450 u | 18.998 u |
| Density | 3.2 g/L | 1.696 g/L |
| Melting point | -102 °C | -220 °C |
| Boiling point | -34 °C | -188 °C |
| Electronegativity | 3.16 | 3.98 |
| First ionisation energy | 1251.2 kJ/mol | 1681 kJ/mol |
| Electron configuration | [Ne] 3s2 3p5 | [He] 2s2 2p5 |
| Discovered by | Carl Wilhelm Scheele | André-Marie Ampère |
Chlorine
Chlorine has two faces. As a free gas it is greenish-yellow, heavier than air and dangerous to breathe, and it was used as a weapon in the First World War. Combined with sodium it is the harmless white crystal you sprinkle on chips. The difference between the two is a single electron, and that electron is the whole story of chlorine.
- Chlorine was the first chemical agent used on a large scale in war, released from cylinders at Ypres in April 1915.
- The swimming pool smell most people call chlorine is mostly chloramines, formed when chlorine reacts with sweat and urine; a well-kept pool smells of very little.
Fluorine
Fluorine is the element that attacks almost everything. It is a pale yellow gas that reacts with glass, sets fire to steel wool and even combines with some of the noble gases. Its pull on electrons is the strongest of any element. For more than seventy years chemists tried to isolate it, and several were injured or killed in the attempt.
- Fluorine is the most electronegative element, with a Pauling value of 3.98.
- Henri Moissan, who first isolated fluorine in 1886, won the Nobel Prize in Chemistry for it in 1906.
Colour the bubbles by density or melting point and the difference jumps out.
More comparisons
Data from Periodic-Table-JSON (CC BY-SA); temperatures rounded to the nearest degree. Written by Anthony.