Periodic Table

Chlorine

Halogen

Quick Facts about Chlorine

S
  • gas- state of matter at room temperature
  • Stable- has at least one stable isotope
  • +7, +5, +1, -1- common oxidation states in compounds
  • ORC- crystal structure, atomic arrangement in solid form
Ar

Chlorine (Cl) is element 17 on the periodic table. Atomic mass of Cl: 35.4500 u. Cl is in period 3, group 17. Melting point of Cl: 171.60 K.Density of Cl: 0.00 g/cm³.

Why Chlorine Matters

The element that purifies your water and seasons your food

In Your Home

  • Table salt (the chloride in sodium chloride)
  • Bleach for cleaning and disinfecting
  • PVC pipes and vinyl flooring
  • Swimming pool sanitizer

Industry Uses

Water TreatmentChlorination has saved millions of lives from waterborne disease
PlasticsPVC (polyvinyl chloride) is the 3rd most produced plastic
Pharmaceuticals25% of medicines contain chlorine
PaperChlorine bleaches wood pulp white

In Your Body

✓ Essential for life

Chloride ions essential for stomach acid (HCl), nerve function, and fluid balance. Your body contains about 95g of chlorine as chloride.

Safety: Chlorine gas is highly toxic (used as WWI weapon). Chloride in salt is safe. Strong chlorine bleach causes burns.

Discovery of Chlorine

Discovered by Carl Wilhelm Scheele in Sweden, 1774

Name origin: Greek: chlôros (greenish yellow).

History & Events

1774
Discovery
Carl Wilhelm Scheele produced chlorine gas, thinking it was a compound containing oxygen
1915
Chemical Warfare
Germany released chlorine gas at Ypres, the first large-scale chemical weapon attack
1908
Water Chlorination
Jersey City became first US city to chlorinate water supply, dramatically reducing disease

About Chlorine

Halogen element. Poisonous greenish-yellow gas. Occurs widely in nature as sodium chloride in seawater. Reacts directly with many elements and compounds, strong oxidizing agent. Discovered by Karl Scheele in 1774. Humphrey David confirmed it as an element in 1810.

Atomic Properties of Cl

Atomic Number of Cl
17
Atomic Mass of Cl
35.4500 u
Electron Configuration
[Ne] 3s2 3p5
Electronegativity
3.16
Block
p-block
Group
17
Period
3

Physical Properties of Cl

Phase (STP)
gas
Melting Point of Cl
171.60 K
Boiling Point of Cl
239.11 K
Density of Cl
0.0032 g/cm3

Thermal Properties

Heat of Fusion
6.41 kJ/mol
Heat of Vaporization
20.41 kJ/mol
Specific Heat
0.48 J/g·K
Molar Heat Capacity
33.95 J/mol·K
Thermal Conductivity
0.01 W/m·K

Atomic Radii

Calculated
100 pm
Covalent
99 pm
Van der Waals
175 pm

Common Misconceptions

Wrong:Pool smell is chlorine.
Correct:That smell is chloramines—chlorine reacting with urine, sweat, and skin oils. A clean pool doesn't smell.
Wrong:Chlorine in pools causes red eyes.
Correct:Red eyes are caused by chloramines and improper pH, not chlorine itself.
Wrong:Chlorine bleach and ammonia make a better cleaner.
Correct:NEVER mix them! This creates toxic chloramine gas. The combination can be fatal.

Isotopes of Chlorine

Chlorine has 2 naturally occurring isotopes, plus 1 notable radioactive isotope.

IsotopeAtomic Mass (u)AbundanceHalf-LifeDecay Mode
3517Cl (Cl-35)Chlorine-35 isotope34.9688526875.76%
3617Cl (Cl-36)Chlorine-36 isotope35.968306810%301,000 yearsβ⁻, β⁺, EC
3717Cl (Cl-37)Chlorine-37 isotope36.965902624.24%

Data source: NIH PubChem (aggregated from IUPAC, NIST)

Isotope Applications

Isotopes of Chlorine have important real-world applications in science and industry.

Geochronology & Dating

Radioactive 36Cl provides a useful tool to determine ages in geology and hydrology. Some radioactive 36Cl is cosmogenic and enters the terrestrial environment in precipitation. Because of its long half-life of 3.01×105 years, the level of 36Cl in aquifers can be measured and used to estimate ages (on the order of 105 to 106 years) of old meteoric groundwater (water that was originally precipitation) [155]. Thermonuclear bomb tests in the ocean produced large amounts of 36Cl by neutron reactions with 35Cl in seawater. This was especially prevalent in the late 1950s. Large amounts of this anthropogenic 36Cl were distributed throughout the atmosphere, deposited with precipitation, and incorporated into terrestrial soils and groundwater. This enriched 36Cl has been used as a tracer of meteoric water from that era [156].

Abundance

Earth's Crust
145.0 mg/kg
Seawater
19.4 g/kg

Uses

Used in water purification, bleaches, acids and many, many other compounds such as chlorofluorocarbons (CFC).

Sources

Salt (sodium chloride, NaCl) is its most common compound. Commercial quantities are produced by electrolysis of aqueous sodium chloride (seawater or brine from salt mines).

Geochemistry

Goldschmidt
litophile
Geochemical Class
semi-volatile

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