Element Name: Chlorine
- Element Symbol: Cl
- Atomic Number: 17
- Group: Group 17
- Classification: Reactive Nonmetal
- Block: p-block
- Electron Configuration: [Ne]3s2 3p5
- Phase at STP: Gas
- Melting Point: 171.6 K (−101.5 °C, −150.7 °F)
- Boiling Point: 239.11 K (−34.04 °C, −29.27 °F)
- Density at STP: 3.2 g/L
- Oxidation States: +7, +6, +5, +4, +3, +2, +1, -1
- Electronegativity (Pauling Scale): 3.16
- Crystal Structure: Orthorhombic
- Magnetic Ordering: Diamagnetic
- Discovery & First Isolation: Carl Wilhelm Scheele (1774)
Atomic Number: 17
"Chlorine is a chemical element with symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is a yellow-green gas at room temperature. It is an extremely reactive element and a strong oxidising agent: among the elements, it has the highest electron affinity and the third-highest electronegativity, behind only oxygen and fluorine."
A Paler Shade of Green
"The most common compound of chlorine, sodium chloride (common salt), has been known since ancient times. Around 1630, chlorine gas was first synthesised in a chemical reaction, but not recognised as a fundamentally important substance. Carl Wilhelm Scheele wrote a description of chlorine gas in 1774, supposing it to be an oxide of a new element. In 1809, chemists suggested that the gas might be a pure element, and this was confirmed by Sir Humphry Davy in 1810, who named it from Ancient Greek khlôros, 'pale green' based on its colour."