Chlorine is a yellow-green gas.
Chlorine gas and chlorine in salt
Elemental chlorine is a yellow-green gas. Table salt is a white solid, and the chlorine in it is present as chloride ions. Saying that something contains chlorine does not tell us which substance it is.
Distinguishing elements, ions and compounds is an important starting point in chemistry. An element identifies an atom type; a substance depends on how atoms or ions are combined.
Salt is different from its elements

SodiumChlorineSalt
Sodium metal, chlorine gas and table salt have different properties. Salt is a compound containing sodium and chlorine.Positive and negative ions in a crystal
A chloride ion has one more electron than a neutral chlorine atom. In salt, negative chloride ions and positive sodium ions form a regular crystal. The diagram shows only a flat section of a three-dimensional structure.
When salt dissolves, its ions spread through the water. They do not simply turn back into elemental chlorine gas. Thinking about the particles helps explain changes that are invisible to our eyes.
Sodium ions (Na⁺) and chloride ions (Cl⁻) form a regular crystal.
A flat section is shown; the real structure extends in three dimensions. This is not an experimental procedure.
Schematic diagram based on reference sourcesSimilar names do not mean identical substances
Chlorine is part of many substances besides salt. Different chlorine-containing compounds are used in water treatment and manufacturing. Their behavior depends on the particular compound and its structure.
Separating the question “which element?” from “which substance?” is useful throughout chemistry. We can apply the same reasoning to diamond and carbon dioxide, or to elemental silicon and quartz.
Temperature and state
25°C: Gas
Illustrative particle motion: sizes, distances and speeds are not to scale. Particles represent atoms or molecules.
← CoolHeat →
Melting point -101.5°C / Boiling point -34.04°C
Pure element at 1 atmosphere. Image conditions are explained in captions. Pictures do not change with temperature.