Generally, there room two species of inorganic compounds that can be formed: ionic compounds and also molecular compounds. Nomenclature is the process of naming civicpride-kusatsu.netical compound with different names so that they can be easily figured out as separate civicpride-kusatsu.neticals. Not natural compounds are compounds that do not deal with the development of carbohydrates, or simply all other compounds that perform not fit right into the summary of an essential compound. For example, essential compounds incorporate molecules with carbon rings and/or chains v hydrogen atom (see picture below). Inorganic compounds, the topic of this section, space every other molecule that does not include these distinctive carbon and hydrogen structures.

You are watching: When to use roman numerals in chemical formulas

Compounds between Metals and Nonmetals (Cation and Anion)

Compounds made of a metal and also nonmetal are commonly known together Ionic Compounds, wherein the link name has actually an ending of –ide. Cations have positive charges if anions have an adverse charges. The net fee of any kind of ionic compound have to be zero which also method it must be electrically neutral. For example, one Na+ is paired v one Cl-; one Ca2+ is paired v two Br-. There are two rule that should be adhered to through:

The cation (metal) is always named first with the name unchanged The anion (nonmetal) is created after the cation, modified to finish in –ide Table 1: Cations and Anions: +1 Charge+2 Charge-1 Charge-2 Charge-3 Charge-4 Charge
Group 1A elements Group 2A elements Group 7A elements Group 6A elements Group 5A elements Group 4A elements
Hydrogen: H+ Beryllium: Be2+ Hydride: H- Oxide: O2- Nitride: N3- Carbide: C4-
Lithium: Li+ Magnesium: Mg2+ Fluoride: F- Sulfide: S2- Phosphide: P3-
Soduim: Na+ Calcium: Ca2+ Chloride: Cl-
Potassium: K+ Strontium: Sr2+ Bromide: Br-
Rubidium: Rb+ Barium: Ba2+ Iodide: I-
Cesium: Cs+

Example 1

Na+ + Cl- = NaCl; Ca2+ + 2Br- = CaBr2

Sodium + Chlorine = sodium Chloride; Calcium + Bromine = Calcium Bromide

The transition metals may kind more than one ion, thus it is needed to be stated which specific ion we space talking about. This is suggested by assigning a Roman numeral after the metal. The Roman numeral denotes the charge and also the oxidation state of the transition metal ion. Because that example, iron can type two usual ions, Fe2+ and also Fe3+. To distinguish the difference, Fe2+ would certainly be called iron (II) and Fe3+ would be named iron (III).

Table of shift Metal and also Metal Cations: +1 Charge+2 Charge+3 Charge+4 Charge
Copper(I): Cu+ Copper(II): Cu2+ Aluminum: Al3+ Lead(IV): Pb4+
Silver: Ag+ Iron(II): Fe2+ Iron(III): Fe3+ Tin(IV): Sn4+
Cobalt(II): Co2+ Cobalt(III): Co3+
Tin(II): Sn2+
Lead(II): Pb2+
Nickel: Ni2+
Zinc: Zn2+

Example 2

Ions: Fe2++ 2Cl- Fe3++ 3Cl-
Compound: FeCl2 FeCl3
Nomenclature Iron (II) Chloride Iron (III) Chloride

However, several of the shift metals" fees have details Latin names. Similar to the other nomenclature rules, the ion the the change metal that has the lower charge has actually the Latin name finishing with -ous and also the one through the the greater charge has actually a Latin name ending with -ic. The most common ones are shown in the table below:

Transition steel Ion v Roman NumeralLatin name
Copper (I): Cu+ Cuprous
Copper (II): Cu2+ Cupric
Iron (II): Fe2+ Ferrous
Iron (III): Fe3+ Ferric
Lead (II): Pb2+ Plumbous
Lead (IV): Pb4+ Plumbic
Mercury (I): Hg22+ Mercurous
Mercury (II): Hg2+ Mercuric
Tin (II): Sn2+ Stannous
Tin (IV): Sn4+ Stannic

Several exceptions use to the Roman character assignment: Aluminum, Zinc, and also Silver. Although castle belong to the change metal category, these steels do not have Roman numerals written after your names since these steels only exist in one ion. Rather of utilizing Roman numerals, the various ions can additionally be presented in level words. The metal is changed to end in –ous or –ic.

-ic finishing is used for the higher oxidation state

Example 3

Compound Cu2O CuO FeCl2 FeCl3
Charge Charge that copper is +1 Charge of copper is +2 Charge of steel is +2 Charge of steel is +3
Nomenclature Cuprous Oxide Cupric Oxide Ferrous Chloride Ferric Chloride

However, this -ous/-ic mechanism is insufficient in some cases, so the roman numeral device is preferred. This mechanism is used generally in naming acids, wherein H2SO4 is commonly known together Sulfuric Acid, and also H2SO3 is well-known as Sulfurous Acid.

Compounds in between Nonmetals and Nonmetals

Compounds that consist the a nonmetal bonded to a nonmetal are frequently known as Molecular Compounds, whereby the facet with the hopeful oxidation state is written first. In many cases, nonmetals kind more than one binary compound, therefore prefixes are offered to identify them.

# of Atoms12345678910
Prefixes Mono- Di- Tri- Tetra- Penta- Hexa- Hepta- Octa- Nona- Deca-

Example 4

CO = carbon monoxide BCl3 = borontrichloride

CO2 = carbon dioxide N2O5 =dinitrogen pentoxide

The prefix mono- is not supplied for the an initial element. If over there is not a prefix before the first element, the is assumed the there is only one atom of the element.

Binary Acids

Although HF have the right to be called hydrogen fluoride, that is provided a various name for focus that the is one acid. An acid is a substance the dissociates right into hydrogen ions (H+) and also anions in water. A quick way to recognize acids is to watch if there is an H (denoting hydrogen) in prior of the molecule formula that the compound. To surname acids, the prefix hydro- is put in prior of the nonmetal modification to finish with –ic. The state of mountain is aqueous (aq) because acids are discovered in water.

Some typical binary acids include:

HF (g) = hydrogen fluoride -> HF (aq) = hydrofluoric acid

HBr (g) = hydrogen bromide -> HBr (aq) = hydrobromic acid

HCl (g) = hydrogen chloride -> HCl (aq) = hydrochloric acid

H2S (g) = hydrogen sulfide -> H2S (aq) = hydrosulfuricacid

It is important to encompass (aq) after the acids since the same compounds can be composed in gas phase v hydrogen named very first followed by the anion finishing with –ide.

Example 5

hypo____ite ____ite ____ate per____ate

ClO- ClO2- ClO3- ClO4-

hypochlorite chlorite chlorate perchlorate


As shown by the arrow, relocating to the right, the adhering to trends occur:

Increasing number of oxygen atoms

Increasing oxidation state that the nonmetal

(Usage of this instance can be checked out from the collection of compound containing Cl and also O)

This occurs due to the fact that the number of oxygen atom are enhancing from hypochlorite come perchlorate, however the in its entirety charge that the polyatomic ion is quiet -1. To effectively specify how numerous oxygen atoms room in the ion, prefixes and suffixes space again used.

Polyatomic Ions

In polyatomic ions, polyatomic (meaning two or much more atoms) are joined with each other by covalent bonds. Although there may be a facet with optimistic charge choose H+, it is not joined with one more element v an ionic bond. This occurs because if the atoms developed an ionic bond, climate it would have already become a compound, thus not needing to get or loose any electrons. Polyatomic anions are more common than polyatomic cations as presented in the graph below. Polyatomic anions have an unfavorable charges when polyatomic cations have actually positive charges. Come indicate different polyatomic ions comprised of the same elements, the name of the ion is modified according to the example below:

Table: common Polyatomic ions Name: Cation/Anion Formula
Ammonium ion NH4+
Hydronium ion


Acetate ion


Arsenate ion


Carbonate ion


Hypochlorite ion


Chlorite ion


Chlorate ion


Perchlorate ion


Chromate ion


Dichromate ion


Cyanide ion


Hydroxide ion


Nitrite ion


Nitrate ion


Oxalate ion


Permanganate ion


Phosphate ion


Sulfite ion


Sulfate ion


Thiocyanate ion

Thiosulfate ion


To integrate the object of acids and also polyatomic ions, over there is nomenclature the aqueous acids. Together acids include sulfuric mountain (H2SO4) or carbonic acid (H2CO3). To surname them, follow this quick, basic rules:

If the ion end in -ate and also is added with one acid, the mountain name will have actually an -ic ending. Examples: nitrate ion (NO3-) + H+ (denoting formation of acid) = nitric mountain (HNO3) If the ion end in -ite and also is added with an acid, then the acid name will have actually an -ous ending. Example: nitite ion (NO2-) + H+ (denoting formation of acid) = nitrous acid (HNO2)


Pettrucci, Ralph H. General civicpride-kusatsu.netistry: principles and contemporary Applications. 9th. Top Saddle River: Pearson Prentice Hall, 2007 Nomenclature of inorganic civicpride-kusatsu.netistry, referrals 1990, Oxford:Blackwell scientific Publications. (1990) Biocivicpride-kusatsu.netical Nomenclature and Related Documents, London:Portland Press, 1992.


1. What is the exactly formula for Calcium Carbonate?

a. Ca+ + CO2-

b. CaCO2-

c. CaCO3

d. 2CaCO3

2. What is the correct surname for FeO?

a. Iron oxide

b. Stole dioxide

c. Iron(III) oxide

d. Iron(II) oxide

3. What is the correct surname for Al(NO3)3?

a. Aluminum nitrate

b. Aluminum(III) nitrate

c. Aluminum nitrite

d. Aluminum nitrogen trioxide

4. What is the exactly formula that phosphorus trichloride?

a. P2Cl2

b. PCl3

c. PCl4

d. P4Cl2

5. What is the correct formula that lithium perchlorate?

a. Li2ClO4

b. LiClO2

c. LiClO

d. No one of these

6. Compose the correct surname for these compounds.

See more: How Many Miles Is 700 Yards To Miles, How Many Miles In 700 Yards

a. BeC2O4:

b. NH4MnO4:

c. CoS2O3:

7. What is W(HSO4)5?

8. Just how do you write diphosphorus trioxide?

9. What is H3P?

10. By adding oxygens to the molecule in number 9, we now have actually H3PO4? What is the surname of this molecule?


1.C; Calcium + carbonate --> Ca2+ + CO32- --> CaCO3

2.D; FeO --> Fe + O2- --> iron must have actually a fee of +2 to make a neutral link --> Fe2+ + O2- --> Iron(II) Oxide

3.A; Al(NO3)3 --> Al3+ + (NO3-)3 --> Aluminum nitrate

4.B; Phosphorus trichloride --> p + 3Cl --> PCl3

5.D, LiClO4; Lithium perchlorate --> Li+ + ClO4- --> LiClO4

6. a. Beryllium Oxalate; BeC2O4 --> Be2+ + C2O42- --> Beryllium Oxalate

b. Ammonium Permanganate; NH4MnO4 --> NH4+ + MnO4- --> Ammonium Permanganate

c. Cobalt (II) Thiosulfate; CoS2O3 --> Co + S2O32- --> Cobalt must have actually +2 fee to do a neutral compund --> Co2+ + S2O32- --> Cobalt(II) Thiosulfate

7. Tungsten (V) hydrogen sulfate

8. P2O3

9. Hydrophosphoric Acid

10. Phosphoric Acid

Contributors and also Attributions

Pui Yan Ho (UCD), Alex Moskaluk (UCD), Emily Nguyen (UCD)

The libraries arePowered through MindTouch®and room supported by the department of education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State university Affordable discovering Solutions Program, and also Merlot. We additionally acknowledge previous national Science structure support under approve numbers 1246120, 1525057, and 1413739. Uneven otherwise noted, content is license is granted byCC BY-NC-SA 3.0. Legal. Have questions or comments? For an ext information call us atinfo check out our status page at