Chlorine connects water treatment, polymers, and salt through different substances. Chlorine gas is reactive and poisonous, while chloride ions are essential components of biological fluids. Chlorine chemistry also contributes to PVC manufacture. Understanding these differences requires identifying the actual chemical species, not just the element name.
FROM ELEMENT TO APPLICATION
AN ELEMENT IN CONTEXT
How can one chlorine-containing polymer serve both pipes and flexible coverings?
Chlorine chemically bound in polyvinyl chloride
FOLLOW THIS RELATIONSHIP
Identify the polymer backbone
PVC contains chlorine chemically bound to a carbon-based polymer framework, so its behavior concerns a macromolecular material rather than free chlorine gas.
Explore the model (optional)
ClFORM → INTERACTION → CONSEQUENCE
Follow the explanation in either direction. These are authored steps, not a physical clock.
Scheele prepared chlorine in 1774, but the gas did not immediately fit a clear elemental category. Chemists interpreted it through theories that gave oxygen an essential role in acids. Davy argued in 1810 that chlorine was itself an element. A substance could therefore be observed accurately while its composition remained misunderstood: recognition required revising the explanatory framework.
1774
Gas prepared
Scheele described the colored gas and its chemical effects.
Chlorine occurs naturally mainly in compounds, including sodium chloride and potassium-bearing salt such as sylvite and carnallite. These sources contain chloride rather than stored chlorine gas. Mineral and salt chemistry therefore provide access to the element through chemical conversion, with properties changing substantially between the starting material and product.
Elemental chlorine is a reactive, colored gas that forms compounds with many other elements. Its reactions underpin bleaching and disinfection, but chloride salts represent a different chemical state. The behavior of a material containing chlorine depends on bonding and concentration, as well as on what other substances are present.
Each section links its supporting references. Descriptions and diagrams were authored for this atlas. Source checks completed. Source checks dated 2026-09-06.
CITE THIS PAGE
Family labels and the group-3 layout are teaching conventions. A table position does not establish an unknown bulk property. Electronic configurations refer to neutral atoms; ions and material environments require their own account.
Read each reference property together with its units, conditions and the reference information below.
Not yet recorded: electron affinity, second ionization energy, ground-state term symbol, van der waals radius, thermal conductivity, specific heat capacity, electrical resistivity, crystal structure, lattice parameter a, space group, abundance in seawater, abundance in the universe, annual production, supply-risk listing, hazard classification, biological role, cas registry number, pubchem cid, wikidata item. These families are declared and awaiting an ingestion run against the source each names; they are listed here rather than shown as empty rows.
Physical
Intended reference: CRC Handbook of Chemistry and Physics · CRC Press
Phase at 20 °C
gas
293.15 K, 101.325 kPa
Melting point in K
171.6 K
at standard pressure unless noted
Boiling point in K
239.11 K
101.325 kPa
Density in g/cm³
0.00321 g/cm³
solids and liquids at 293 K; gases at 273 K and 101.325 kPa
Atomic and electronic
Intended reference: Pauling electronegativity scale · Widely tabulated; original in The Nature of the Chemical Bond
Electronegativity in Pauling
3.16 Pauling
Pauling scale
First ionization energy in kJ/mol
1251 kJ/mol
gas-phase neutral atom, ground state
Covalent radius in pm
102 pm
single-bond covalent radius
Common oxidation states
-1, +1, +3, +5, +7
states met in ordinary compounds; not exhaustive
Occurrence and identity
Intended reference: CRC Handbook of Chemistry and Physics · CRC Press
Abundance in the crust in mg/kg
145 mg/kg
upper continental crust, mass fraction
Has stable isotopes
Yesderived
Discovery year in CE
1774 CEderived
WHERE IT SITS AMONG ITS NEIGHBORS
Electronegativity across period 3
Cl 3.16 Pauling · Chlorine
Electronegativity across period 3. Exact values.
Na
0.93
Mg
1.31
Al
1.61
Si
1.9
P
2.19
S
2.58
Cl
3.16
Electronegativity down group 17
Cl 3.16 Pauling · Chlorine
Electronegativity down group 17. Exact values.
F
3.98
Cl
3.16
Br
2.96
I
2.66
At
2.2
The trend uses the same reference-property values as the periodic table. Elements with no recorded value are left out of the line rather than drawn at zero.
