Element identity
Atomic number, symbol, relative atomic mass display and periodic position are established reference data.
Atomic / electronic model
Ground-state electron configuration and atomic reference values are compiled/evaluated data; orbital graphics are teaching probability models, not photographs.
Material / molecular structure
The displayed ordinary structure is based on established material or molecular science; simplified viewers are labelled as teaching schematics where exact crystallographic coordinates are not rendered.
Temperature / phase path
Transition values are reference/evaluated values for the stated teaching path; pressure, purity and allotropy can matter.
Geography
Real pins use reviewed place/dataset context. Conceptual layers are used when country pins would imply false occurrence, unsafe inventory or an incomplete global distribution.
The lens describes evidence status, not confidence theatre. “Unknown” is kept unknown, and teaching schematics are not presented as direct measurements.
Chlorine (Cl)
Chlorine is a Group 17 halogen with seven valence electrons. Elemental chlorine is normally the diatomic molecule Cl₂, while chloride Cl⁻ is the much more familiar form in salts, seawater, biology and many materials.
Chlorine atomic number, mass, electron configuration and key properties
Chlorine: quick answers
How many protons, neutrons and electrons does chlorine have?
Chlorine’s atomic number is 17, so every chlorine atom has 17 protons, and a neutral atom also has 17 electrons. Its most common natural isotope, chlorine-35, has 18 neutrons (other isotopes have different neutron counts).
What is the symbol for chlorine?
The chemical symbol for chlorine is Cl.
Is chlorine a solid, liquid or gas at room temperature?
Chlorine is a gas at room temperature (about 25 °C).
What family (group) is chlorine in?
Chlorine is a halogen, in group 17, period 3 of the periodic table.
How many valence electrons does chlorine have?
Chlorine has 7 valence electrons, the electrons in its outer shell, which matches its position in group 17.
What is the electron configuration of chlorine?
The ground-state electron configuration of chlorine is [Ne] 3s² 3p⁵.
From atomic number to chemistry
Read these as a chain of causes, not as isolated facts. Each step links to the concept hub if you want the underlying idea explained.
Seventeen protons define chlorine; neutral Cl also has 17 electrons.
Seven valence electrons place chlorine one electron short of a closed outer shell.
Gaining one electron gives chloride, Cl-.
Chlorine is a halogen, between sulfur and argon across Period 3.
Two stable isotopes dominate natural chlorine and shape its standard atomic weight.
Chlorine in its period and family
Chlorine lies in Period 3, Group 17, directly below fluorine and above bromine. Its seven-valence-electron pattern makes gaining one electron to form chloride a common chemical outcome.
Chlorine Visual Lab
Decode chlorine’s tile, compare neutral Cl with Cl⁻ electron counts, inspect a ³⁵Cl teaching nucleus, 3s/3p probability models and a Cl₂ molecular view, then connect chlorine to chloride chemistry, water treatment and industrial materials.
Every mark points to one exact feature
The numbered markers explain the same information system used throughout Element Lookup. Unknown or predicted fields remain visibly labelled rather than being replaced with guesses.
Chlorine in one minute
Atomic number 17 means every chlorine nucleus has 17 protons.
The neutral configuration [Ne] 3s² 3p⁵ gives seven valence electrons.
Elemental chlorine at ordinary conditions is Cl₂, a green-yellow gas.
Natural chlorine is dominated by stable ³⁵Cl and ³⁷Cl.
Chloride ions are widespread in salts, seawater and biology and must not be confused with Cl₂ gas.
Shell rings organize electron counts. They are not electron trajectories or orbital shapes.
2 · 8 · 7 electrons
The 3s probability model has two radial nodes; the occupied 3p model has one radial node and a selectable p orientation. The buttons show representative atomic orbitals, while Cl₂ bonding requires molecular-orbital/bonding ideas beyond an isolated-atom picture.
Diatomic chlorine molecule at ordinary conditions; low-temperature solid chlorine is a molecular solid. The viewer is evidence-aware: measured structures are identified as such; unknown bulk structures stay unknown.
Teaching visualization; not a literal finite sample or thermal trajectory.What this model does—and does not—show
The 3s probability model has two radial nodes; the occupied 3p model has one radial node and a selectable p orientation. The buttons show representative atomic orbitals, while Cl₂ bonding requires molecular-orbital/bonding ideas beyond an isolated-atom picture.
Where do I meet chlorine?
Clickable learning cards connect the element to materials, environment, technology, biology or research - depending on what the evidence actually supports.
Water treatment
Controlled chlorine chemistry is widely used to disinfect drinking water and swimming-pool water.
Chlorine atom, Cl2 molecule and chloride ion are not interchangeable
Three closely related labels describe different chemical objects with very different behavior.
Neutral atom
The isolated atom has seven valence electrons and is not the ordinary elemental gas.
Fluorine, chlorine and bromine
The halogens share seven valence electrons, but molecular size and intermolecular forces change strongly down the group, giving very different ordinary physical states.
| Valence | 2s² 2p⁵ |
|---|---|
| Ordinary form | F₂ gas |
| Valence | 3s² 3p⁵ |
|---|---|
| Ordinary form | Cl₂ gas |
| Common ion | Cl⁻ |
| Valence | 4s² 4p⁵ |
|---|---|
| Ordinary form | Br₂ liquid |
Chlorine properties: atomic, physical, thermal and chemical
Categories follow the science of this element rather than a fixed decorative template. Each row carries condition/provenance context and an evidence label; unknown values stay unknown.
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Atomic number | 17 | Source-reviewed; see Sources below | Evaluated |
| Relative atomic mass | 35.45 | Source-reviewed; see Sources below | Evaluated |
| Ground-state electron configuration | [Ne] 3s² 3p⁵ | Source-reviewed; see Sources below | Evaluated |
| Group / period / block | Group 17 · Period 3 · p-block | Periodic-table placement | Evaluated |
| Electronegativity | 3.16 | Source-reviewed; see Sources below | Evaluated |
| Reference isotope | ³⁵Cl | Source-reviewed; see Sources below | Evaluated |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| State context | Gas as Cl₂ at 20 °C | Source-reviewed; see Sources below | Evaluated |
| Density | 0.002898 g/cm³ | Source-reviewed; see Sources below | Evaluated |
| Material / molecular structure | Cl₂ molecule | Diatomic chlorine molecule at ordinary conditions; low-temperature solid chlorine is a molecular solid | Measured |
| Classification | Halogen · nonmetal | Periodic-table / chemistry classification | Evaluated |
| Structure-model scope | Diatomic chlorine molecule at ordinary conditions; low-temperature solid chlorine is a molecular solid | Teaching visualization; exact crystallographic coordinates are not implied unless stated. | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Melting / transition reference | 171.7 K | Source-reviewed; see Sources below | Evaluated |
| Boiling / gas reference | 239.11 K | Source-reviewed; see Sources below | Evaluated |
| Phase-path context | At approximately standard pressure, chlorine is solid below about 171.7 K, liquid from about 171.7 K to 239.11 K, and gaseous above about 239.11 K. | Shared phase registry drives the slider, regions and markers. | Evaluated |
| Condition warning | Temperature and pressure define phase behavior; purity/allotropy may matter. | Teaching condition statement | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Common oxidation states | −1 common; positive states in oxycompounds | Source-reviewed; see Sources below | Evaluated |
| Ion / common ion context | Cl⁻ | Source-reviewed; see Sources below | Evaluated |
| Periodic chemistry context | Chlorine lies in Period 3, Group 17, directly below fluorine and above bromine. Its seven-valence-electron pattern makes gaining one electron to form chloride a common chemical outcome. | Element-specific interpretation | Reviewed |
| Chemistry caution | Elemental form, ions and compounds are distinct chemical objects. | Interpretive teaching rule | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| ³⁵Cl | Stable · ≈75.77% natural abundance | The more abundant stable isotope; 17 protons and 18 neutrons. | Evaluated |
| ³⁷Cl | Stable · ≈24.23% natural abundance | The second stable natural isotope; its abundance contributes strongly to chlorine’s standard atomic weight. | Evaluated |
| Teaching nucleus | ³⁵Cl · 17 protons + 18 neutrons | Reference isotope used in the nucleus model | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Page evidence note | Atomic/isotope and phase data are measured/evaluated. Geography distinguishes natural chloride reservoirs from industrial chlorine networks. Elemental chlorine hazards are described at a high level only. | Evidence summary for this guide | Reviewed |
| Structure evidence | Diatomic chlorine molecule at ordinary conditions; low-temperature solid chlorine is a molecular solid | Measured structure, labelled schematic, prediction or explicit unknown as applicable. | Reviewed |
| Map evidence rule | Real pins are reviewed examples; conceptual layers are used when pins would mislead. | Geography Explorer 2.0 | Reviewed |
| Source set | 3 primary/reference links listed below | Open the Sources section for the actual references. | Reviewed |
Is Chlorine a solid, liquid or gas? State at temperature
At approximately standard pressure, chlorine is solid below about 171.7 K, liquid from about 171.7 K to 239.11 K, and gaseous above about 239.11 K.
Where on Earth is Chlorine found or produced?
Who discovered Chlorine, and when?
Carl Wilhelm Scheele prepared chlorine gas and described its properties, although he did not recognize it as an element.
Humphry Davy argued that the gas was an element and named it chlorine from the Greek chloros, referring to its greenish-yellow color.
Chlorine chemistry became important in bleaching, sanitation, water treatment and large-scale chemical manufacturing.
Chlorine is a major industrial chemical, while chloride chemistry is central to geochemistry and biology.
From chloride-rich brine to chlorine chemistry: high-level context
Natural chloride is abundant in seawater and salt deposits; elemental chlorine is not mined as a free gas resource.
Industrial chlor-alkali systems use purified brine and electrochemistry to make chlorine alongside other products.
Chlorine is converted into many compounds and materials or used under controlled conditions for disinfection.
Because Cl₂ is toxic and reactive, Element Lookup keeps this discussion conceptual and does not provide generation or handling instructions.
What is chlorine used for?
Water disinfection
Chlorine chemistry helps control disease-causing microorganisms in treated water.
Chemical manufacturing
Chlorine is a major feedstock/intermediate in a wide range of industrial chemistry.
PVC
Chlorine is incorporated into polyvinyl chloride, a major polymer used in construction and other applications.
Bleaching & sanitation
Chlorine-containing oxidants such as hypochlorites are widely used for bleaching and disinfection.
Chlorine isotopes and natural abundance
³⁵Cl
Stable · ≈75.77% natural abundanceThe more abundant stable isotope; 17 protons and 18 neutrons.
³⁷Cl
Stable · ≈24.23% natural abundanceThe second stable natural isotope; its abundance contributes strongly to chlorine’s standard atomic weight.
Five-question Chlorine check
How many valence electrons does neutral chlorine have?
What is the ordinary elemental form of chlorine?
Which statement is correct?
Which two stable isotopes dominate natural chlorine?
Where is chlorine placed in the periodic table?
Chlorine questions students commonly ask
Each answer starts with the direct fact, then explains the chemistry, evidence or material context so the result is understandable rather than merely memorized.
Is chlorine a metal or nonmetal?
Short answer: Chlorine is a nonmetal and a halogen in Group 17.
This guide classifies Chlorine as a halogen · nonmetal. Its periodic position is Period 3, p-block, Group 17. Chlorine lies in Period 3, Group 17, directly below fluorine and above bromine. Its seven-valence-electron pattern makes gaining one electron to form chloride a common chemical outcome.
Key point: Periodic-table classification describes recurring atomic/chemical behavior; it does not make every element in a column physically identical.
How many valence electrons does chlorine have?
Short answer: Seven. The neutral configuration ends 3s² 3p⁵.
The neutral-atom ground-state reference used on this page is [Ne] 3s² 3p⁵. This is an isolated-atom reference: bonding and ion formation can change which outer electrons are present or chemically active. The listed common oxidation-state context is −1 common; positive states in oxycompounds, which helps connect the atomic configuration to ordinary chemistry without treating electron counting as a single universal rule.
Key point: Electron configuration is a ground-state atomic reference, not a literal picture of every compound.
How many protons, neutrons and electrons does chlorine have?
Short answer: All chlorine atoms have 17 protons. A neutral atom has 17 electrons. The common isotope ³⁵Cl has 18 neutrons, while ³⁷Cl has 20.
Atomic number is defined by proton count, so 17 protons are what make an atom chlorine. A neutral chlorine atom also has 17 electrons, while isotopes can have different neutron counts without changing the element.
Key point: Atomic number = proton count.
What color is chlorine?
Short answer: Elemental chlorine gas is yellow-green. Chloride salts can be colorless or have colors determined by other ions; they should not be confused with Cl₂.
The ordinary elemental-material description used here is: Gas as Cl₂ at 20 °C. “Chlorine” and “chloride” are not interchangeable. Toxic green-yellow Cl₂ gas is elemental chlorine; chloride ions such as those in sodium chloride have very different properties.
Key point: Elemental appearance can differ from the colors of its ions, compounds, oxide films or host materials.
Is chlorine a gas?
Short answer: At ordinary room conditions elemental chlorine is a diatomic gas, Cl₂. It can be liquefied or frozen at sufficiently low temperatures.
Elemental chlorine at ordinary conditions is Cl₂, a green-yellow gas. Diatomic chlorine molecule at ordinary conditions; low-temperature solid chlorine is a molecular solid.
Key point: Use the direct answer together with the material, isotope and evidence context shown elsewhere on the page.
What is chlorine used for?
Short answer: Major uses include water disinfection and manufacture of many chemicals and materials, including PVC.
Water disinfection: Chlorine chemistry helps control disease-causing microorganisms in treated water. Chemical manufacturing: Chlorine is a major feedstock/intermediate in a wide range of industrial chemistry. “Chlorine” and “chloride” are not interchangeable. Toxic green-yellow Cl₂ gas is elemental chlorine; chloride ions such as those in sodium chloride have very different properties.
Key point: Always distinguish the pure element from the compound, alloy, isotope or device material that actually performs the application.
Scientific sources for Chlorine
- Royal Society of Chemistry - Chlorine
- NIST - Atomic Data for Chlorine
- CDC/ATSDR - Chlorine toxicological context
Questions to ask next about Chlorine
A good element lesson should lead to the next useful question, not end after a list of facts.
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