Ions Reference
Cations and anions you will meet constantly: how they form, how they are named, and where they appear.
Acetate ion (1-)
The acetate ion is the conjugate base of acetic acid, made of two carbons, three hydrogens, and two oxygens. It gives vinegar its chemistry and forms widely used salts and esters.
Aluminium ion (3+)
The aluminium ion carries a triple positive charge, formed when aluminium loses its three outer electrons. Small and highly charged, it pulls strongly on nearby negative ions and water molecules.
Ammonium ion (1+)
The ammonium ion is a polyatomic cation of one nitrogen bonded to four hydrogens. It is the main nitrogen form in fertilizers and a key part of the nitrogen cycle.
Bicarbonate ion (1-)
The bicarbonate ion is a carbonate ion carrying one hydrogen. It is the body's main blood buffer and the active ingredient in baking soda.
Bromide ion (1-)
The bromide ion is a bromine atom that has gained one electron. It occurs naturally in seawater and was once widely used in sedative medicines and photographic film.
Calcium ion (2+)
The calcium ion carries a double positive charge and forms when a calcium atom loses both of its outer electrons. It is vital for bones, teeth, muscle contraction, and cell signaling.
Carbonate ion (2-)
The carbonate ion is a flat, triangular anion of carbon and oxygen. It builds limestone, chalk, and marble, and controls the acidity of oceans and blood.
Chloride ion (1-)
The chloride ion is a chlorine atom that has gained one electron. It is abundant in seawater, table salt, and blood plasma, and essential for digestion as part of stomach acid.
Chromate ion (2-)
The chromate ion is a yellow tetrahedral anion of chromium and oxygen. In acidic solution it converts to orange dichromate, a classic equilibrium demonstration.
Copper(II) ion (2+)
The copper(II) ion is a doubly charged ion that colors water solutions a striking blue. It is the most common ion of copper and appears in many pigments and fungicides.
Cyanide ion (1-)
The cyanide ion is a polyatomic anion of carbon triple-bonded to nitrogen. It is extremely toxic because it blocks cells from using oxygen, and it is used industrially in metal extraction.
Hydride ion (1-)
The hydride ion is a hydrogen atom that has gained an extra electron, giving it a negative charge. It is a powerful reducing agent found in ionic metal hydrides.
Hydrogen ion (1+)
The hydrogen ion is a single proton: a hydrogen atom that has lost its only electron. Its concentration in water defines the pH scale and therefore the acidity of every aqueous solution.
Hydronium ion (1+)
The hydronium ion is a water molecule with an extra proton attached. It is the actual form of the hydrogen ion in water and the species whose concentration the pH scale measures.
Hydroxide ion (1-)
The hydroxide ion is a polyatomic anion made of one oxygen and one hydrogen atom. It defines basic solutions: any water solution with more hydroxide than hydrogen ions is a base.
Iodide ion (1-)
The iodide ion is an iodine atom that has gained one electron. It is the form of iodine the thyroid gland needs to make hormones, so it is added to table salt in many countries.
Iron(II) ion (2+)
The iron(II) ion forms when an iron atom loses two electrons. It is a pale green ion in solution and the form of iron carried by hemoglobin in the blood.
Iron(III) ion (3+)
The iron(III) ion forms when an iron atom loses three electrons. It gives a yellow-brown color to solutions and is the stable oxidation state of iron in rust.
Magnesium ion (2+)
The magnesium ion is a doubly charged positive ion formed when magnesium loses its two outer electrons. It sits at the center of every chlorophyll molecule and is essential for hundreds of enzymes.
Nitrate ion (1-)
The nitrate ion is a flat, triangular polyatomic anion of nitrogen and oxygen. It is the main nitrogen nutrient plants absorb and a powerful oxidizing agent in concentrated nitric acid.
Nitride ion (3-)
The nitride ion is a single nitrogen atom that has gained three electrons. It is found in ceramic nitrides such as boron nitride and silicon nitride, which are extremely hard materials.
Nitrite ion (1-)
The nitrite ion is a bent polyatomic anion of nitrogen and oxygen. It is used to preserve cured meats and also forms in the environment as bacteria convert ammonia to nitrate.
Oxide ion (2-)
The oxide ion is an oxygen atom that has gained two electrons. It is the building block of metal oxides, from rust and lime to the ceramics in electronics.
Permanganate ion (1-)
The permanganate ion is a deep purple anion of manganese and oxygen. It is a powerful oxidizing agent used in disinfectants, water treatment, and redox titrations.
Phosphate ion (3-)
The phosphate ion is a tetrahedral anion of phosphorus and oxygen. It forms the backbone of DNA, carries energy in ATP, and strengthens bones and teeth.
Potassium ion (1+)
The potassium ion is a singly charged positive ion formed when a potassium atom loses its outer electron. It is the main positive ion inside animal cells and an essential plant nutrient.
Silver ion (1+)
The silver ion is a singly charged positive ion of silver. It is strongly antibacterial and forms light-sensitive compounds used in traditional photography.
Sodium ion (1+)
The sodium ion is a single-charged positive ion formed when a sodium atom loses its outer electron. It is one of the most abundant ions in seawater and in the human body.
Sulfate ion (2-)
The sulfate ion is a tetrahedral polyatomic anion of sulfur and oxygen. It is one of the most common ions in minerals, seawater, and laboratory reagents.
Sulfide ion (2-)
The sulfide ion is a sulfur atom that has gained two electrons. It is responsible for the rotten-egg smell of hydrogen sulfide and gives deep colors to many metal sulfide ores.
Sulfite ion (2-)
The sulfite ion is a pyramid-shaped polyatomic anion of sulfur and oxygen. It is used as a preservative in dried fruit and wine, where it prevents browning and bacterial growth.
Zinc ion (2+)
The zinc ion is a doubly charged positive ion and the only common ion of zinc. It is colorless in solution and essential for enzymes, immune function, and wound healing.