[4] It is an essential electrolyte located in all body fluids responsible for maintaining acid/base balance, transmitting nerve impulses and regulating liquid flow in and out of cells.

The chlorine atom's hold on the valence shell is weaker because the chloride anion has one more electron than it does.

In terms of its acid–base properties, chloride is a weak base as indicated by the negative value of the pKa of hydrochloric acid.

[10] Most chloride salts are soluble in water, thus, chloride-containing minerals are usually only found in abundance in dry climates or deep underground.

Chloride has a major physiological significance,[11] which includes regulation of osmotic pressure, electrolyte balance and acid-base homeostasis.

[13][14] Chloride is an essential electrolyte, playing a key role in maintaining cell homeostasis and transmitting action potentials in neurons.

Chloride is usually (though not always) at a higher extracellular concentration, causing it to have a negative reversal potential (around −61 mV at 37 °C in a mammalian cell).

[20] The presence of chlorides, such as in seawater, significantly worsens the conditions for pitting corrosion of most metals (including stainless steels, aluminum and high-alloyed materials).

[21] Increased concentrations of chloride can cause a number of ecological effects in both aquatic and terrestrial environments.

It may contribute to the acidification of streams, mobilize radioactive soil metals by ion exchange, affect the mortality and reproduction of aquatic plants and animals, promote the invasion of saltwater organisms into previously freshwater environments, and interfere with the natural mixing of lakes.

The process involves two parallel reactions: An example is table salt, which is sodium chloride with the chemical formula NaCl.

In addition, calcium chloride is widely used as a de-icer, since it is effective in lowering the melting point when applied to ice.