Chlorine

Reactive nonmetal · atomic number 17

1735.45ClChlorineGasReactive nonmetal

Chlorine is a chemical element with symbol Cl and atomic number 17. It also has a relative atomic mass of 35.5. Chlorine is in the halogen group (17) and is the second lightest halogen following fluorine.

Properties of Chlorine

Element category	Reactive nonmetal
Atomic number	17
Atomic mass	35.45 u
Phase at STP	Gas
Group	17
Period	3
Block	p
Electron configuration	[Ne] 3s2 3p5
Electrons per shell	2, 8, 7
Electronegativity (Pauling)	3.16
Melting point	171.6 K (-102 °C)
Boiling point	239.11 K (-34 °C)
Density	3.2 g/L
Discovered by	Carl Wilhelm Scheele

← Sulfur · Periodic table · Argon → Ar

About the reactive nonmetal group

Elements that readily gain or share electrons — the building blocks of water, air, living tissue and most organic chemistry.

Data: Periodic-Table-JSON (CC BY-SA 3.0) · stored statically on our server. https://en.wikipedia.org/wiki/Chlorine

Explore by category — Periodic Table /unsur

⚛️ Full periodic table

All 118 chemical elements on one interactive, colour-coded table, each linking to a fact file and plain-language summary.

🧪 Reactive nonmetal

11 elements: Elements that readily gain or share electrons — the building blocks of water, air, living tissue and most organic chemistry.

🧪 Noble gas

6 elements: Full outer electron shells make these gases almost inert: they barely react, glow in discharge lamps and are used to create unreactive atmospheres.

🧪 Alkali metal

6 elements: Soft, wildly reactive metals of group 1 — they fizz in water and never occur pure in nature. Lithium, sodium, potassium and friends.

🧪 Alkaline earth metal

6 elements: Reactive group-2 metals a step calmer than the alkalis: magnesium, calcium and the structural and biological workhorses among them.

🧪 Transition metal

35 elements: The dense, strong, catalytic heart of the table — iron, copper, gold, titanium — responsible for most of metallurgy, jewellery and industry.

🧪 Post-transition metal

9 elements: Softer, lower-melting metals beside the transition block — aluminium, tin, lead — abundant in cans, foils, solders and pigments.

🧪 Metalloid

7 elements: In-between elements that behave as semiconductors: silicon, germanium and boron underpin electronics, glass and solar cells.

🧪 Lanthanide

15 elements: The rare-earth “inner transition” metals that give strong permanent magnets, screen phosphors and catalyst polish.

🧪 Actinide

15 elements: Mostly radioactive, heavy metals — several made only in reactors — whose fission powers nuclear energy and weapons.

🧪 Unknown properties

8 elements: Superheavy synthetic elements made atom-by-atom, existing for fractions of a second; their true chemistry is still unmeasured.