Naming Compounds - General Chemistry

Use the following worksheets to learn how to name compounds and write formulas.  If the formula is given, write down the name, and if the name is given write down the formula.  Use these pages as a study guide.

As a general rule, you should know the names and symbols for elements 1-36.  In addition, you should know names and symbols for all elements in Groups I and II, as well as the halogens (Group VII), noble gases (Group VIII), and some other metals used frequently.  These metals include Ag (silver), Au (gold), Pb (lead), Sn (tin), and Cd (cadmium).

When naming compounds, remember the following rules:

Binary Ionic Compounds (Type I)

  1. The cation (positively charged ion; Na+, Al3+) is always named first and the anion (negatively charged ion; Cl-, O2-) second.
  2. A monatomic (meaning one-atom) cation takes its name from the name of the element.  For example, Na+ is called sodium in the names of compounds containing this ion.
  3. A monatomic anion is named by taking the root of the element name and adding -ide.  Thus, the Cl- ion is called chloride, the S2- ion is called sulfide, and the O2- ion is called oxide.

Some common monatomic cations and anions are shown below
Cation Name Cation Name   Anion Name Anion Name
H+ Hydrogen Li+ Lithium   H- Hydride F- Fluoride
Na+ Sodium K+ Potassium   Cl- Chloride Br- Bromide
Cs+ Cesium Be2+ Beryllium   I- Iodide O2- Oxide
Mg2+ Magnesium Ca2+ Calcium   S2- Sulfide Se2- Selenide
Ba2+ Barium Al3+ Aluminum   N3- Nitride P3- Phosphide
Zn2+ Zinc Ag+ Silver   As3- Arsenide C4- Carbide

Binary Ionic Compounds (Type II)

  1. The cation of a transition metal is always named first (like any cation) and the anion second.
  2. A monatomic (meaning one-atom) cation takes its name from the name of the element.  For example, Cu+ is called Copper(I) and Cu2+ is called Copper(II) in the names of compounds containing these ions.  The number in parentheses is the charge of the cation.
  3. All transition metal cations, except Zn2+, Cd2+, and Ag+ (which always have the charges shown here), must show the oxidation number (charge) in parantheses following the English spelling of the element, such as Iron(III), Copper(I), or Vanadium(V), whenever a compound containing these ions, which have multiple charges, is named.
  4. For the cations in Groups IIIA-VIA (including, Sn, Pb, Ga, Bi, etc.) also have multiple charges, even though they are not transition metals.  For all the metals in these groups (except Al, which, of course, always has a +3 charge), include a paranthesis after the name, and show its positive charge as a Roman numeral (Pb2+ is Lead(II) in names)

Binary Covalent Compounds (Type III)

Compounds containing only non-metal elements are named using Type III binary compound rules.  These compounds are always neutral (not ions which have charges), and consist of only two elements (see acid naming below for compounds containing only non-metal elements, but with more than two elements.  The prototypical compound is CO2, which is called carbon dioxide.

  1. The first element shown in the compound is named as the element (e.g., for CO2, first element is "carbon")
  2. The second element shown in the compound is named according to the anion name, ending in -ide (e.g., for CO2, the second element is named "oxide")
  3. The second element always carries a prefix indicating the number of times it is present in the compound (e.g., for CO2, the second element (oxide) is present twice, so it has the "di" prefix)
  4. The amount of the first element is only shown, if it is present more than once.  It is assumed to be present only once, hence just the name of the element.  However, if it is present more than once, you must then specify the number of times it is duplicated (di, tri, tetra, etc.)

The following prefixes are used to specify the number of times an element is present in binary covalent compounds:

prefixes (1-5) prefixes (6-10) Examples using prefixes
  • 1 — mono
  • 2 — di
  • 3 — tri
  • 4 — tetra
  • 5 — penta
  • 6 — hexa
  • 7 — hepta
  • 8 — octa
  • 9 — nona
  • 10 — deca
  • CCl4 — carbon tetrachloride
  • P2O5 — diphosphorus pentoxide
  • N2O — ninitrogen monoxide
  • ICl3 — iodine trichloride

Please note that ionic compounds (Type I & II binary compound names) never use prefixes to specify how many times an element is present.  Prefixes are only used for covalent compounds formed from non-metal elements.

Common Acid and Anion Names

Acids are compounds containing an ionizable proton (H+), since an acid is a proton donor (a hydrogen atom which has lost its electron).  The polyatomic anions derived from acids are named by dropping the -ic (or -ous) suffix from the acid name and adding the -ate (or -ite) suffix, respectively.  Compounds containing polyatomic anions are named using the Type I or Type II naming systems described above.  For example, the sodium salt of nitric acid is sodium nitrate (NaNO3).  If you know the acid formula you will always get the correct anion formula and its charge, since the charge is equal to the number of ionizable hydrogen atoms in the acid, and is always negative.  For example, for sulfuric acid (H2SO4), the anion is sulfate (SO42-) with a -2 charge.

Acids which do not contain oxygen (e.g., HCl, H2S, HF) are named by adding the hydro- prefix to the root name of the element, followed by the -ic suffix.  HCl is hydrochloric acid, H2S is hydrosulfuric acid, and HF is hydrofluoric acid (italics added for emphasis).  Anions of these acids, which contain a single element (not polyatomic), are named as a regular non-metal anion (i.e., Cl- is chloride, S2- is sulfide, and F- is fluoride).

Acid Name Anion Name    Acid Name Anion Name
H2SO4 sulfuric SO42- sulfate   HCl hydrochloric Cl- chloride
HNO3 nitric NO3- nitrate   HBr hydrobromic Br- bromide
H3PO4 phosphoric PO43- phosphate   HClO3 chloric ClO3- chlorate
HC2H3O2 acetic C2H3O2- acetate   HClO2 chlorous ClO2- chlorite
H2SO3 sulfurous SO32- sulfite   HBrO3 bromic BrO3- bromate
HNO2 nitrous NO2- nitrite   HBrO hypobromous BrO- hypobromite