Science, Tech, Math › Science Common Anions Table and Formulas List An anion is an ion that has a negative charge Share Flipboard Email Print Anions are chemical species that carry a negative electrical charge. Comstock/Getty Images Science Chemistry Periodic Table Basics Chemical Laws Molecules Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate by Anne Marie Helmenstine, Ph.D. Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. Updated February 04, 2019 An anion is an ion that has a negative charge. Here is a table listing common anions and their formulas: Table of Common Anions Simple Anions Formula Hydride H- Oxide O2- Fluoride F- Sulfide S2- Chloride Cl- Nitride N3- Bromide Br- Iodide I- Oxoanions Formula Arsenate AsO43- Phosphate PO43- Arsenite AsO33- Hydrogen Phosphate HPO42- Dihydrogen Phosphate H2PO4- Sulfate SO42- Nitrate NO3- Hydrogen Sulfate HSO4- Nitrite NO2- Thiosulfate S2O32- Sulfite SO32- Perchlorate ClO4- Iodate IO3- Chlorate ClO3- Bromate BrO3- Chlorite ClO2- Hypochlorite OCl- Hypobromite OBr- Carbonate CO32- Chromate CrO42- Hydrogen Carbonate or Bicarbonate HCO3- Dichromate Cr2O72- Anions from Organic Acids Formula Acetate CH3COO- Formate HCOO- Other Anions Formula Cyanide CN- Amide NH2- Cyanate OCN- Peroxide O22- Thiocyanate SCN- Oxalate C2O42- Hydroxide OH- Permanganate MnO4- Writing Formulas of Salts Salts are compounds composed of cations bonded to anions. The resulting compound carries a neutral electrical charge. For example, table salt, or sodium chloride, consists of the Na+ cation bonded to the Cl- anion to form NaCl. Salts are hygroscopic, or tend to pick up water. This water is called water of hydration. By convention, the cation name and formula are listed before the anion name and formula. In other words, write the cation on the left and the anion on the right. The formula of a salt is: (cation)m(anion)n·(#)H2O where the H2O is omitted if the # is zero, m is the oxidation state of the anion, and n is the oxidation state of the anion. If m or n is 1, then no subscript is written in the formula. The name of a salt is given by: (cation)(anion) (prefix)(hydrate) where the hydrate is omitted if there is no water. Prefixes indicate the number of water molecules or can be used in front of the cation and anion names in cases where the cation (usually) can have multiple oxidation states. Common prefixes are: Number Prefix 1 mono 2 di 3 tri 4 tetra 5 penta 6 hexa 7 hepta 8 octa 9 nona 10 deca 11 undeca For example, the compound strontium chloride consists of the cation Sr2+ combined with the anion Cl-. It is written SrCl2. When the cation and/or the anion is a polyatomic ion, parentheses may be used to group the atoms in the ion together to write the formula. For example, the salt ammonium sulfate consists of the cation NH4+ and the sulfate anion SO42-. The formula of the salt is written as (NH4)2SO4. The compound calcium phosphate consists of the calcium cation Ca2+ with the anion PO43- and is written as Ca3(PO4)2. An example of a formula that includes water of hydrate is that of copper(II) sulfate pentahydrate. Note that the name of the salt includes the oxidation state of copper. This is common when dealing with any transition metal or rare earth. The formula is written as CuSO4·5H2O. Formulas of Binary Inorganic Compounds Combining cations and anions to form binary inorganic compounds is simple. The same prefixes are applied to indicate the quantities of cation or anion atoms. Examples include the name of water, H2O, which is dihydrogen monoxide, and the name of NO, which is nitrogen dioxide. Cations and Anions in Organic Compounds The rules for naming and writing the formulas of organic compounds are more complex. In general, the name follows the rule: (group prefixes)(longest carbon chain prefix)(highest root bond)(most important group suffix) Continue Reading Chemistry Basics: What Is an Anion? How to Name Ionic Compounds How Formulas of Ionic Compounds Work Check Common Cations for Chemistry with This Handy Table What Is an Ion? Definition and Examples What Water of Crystallization Means in Chemistry Do You Know How to Tell Cation and Anion Ions Apart? How to Understand the Difference Between an Atom and an Ion Learn How to Assign Oxidation States from a Worked Example Problem What Is a Chemical Compound? What Spectator Ions Are and Why They Are Important Without Ionic Bonds, There Would Be No Table Salt Know the Rules for Assigning Oxidation Numbers An Introduction to Qualitative Analysis What Is the Common-Ion Effect? What Is Water of Hydration?