inorganic chemistry nomenclature -...

Inorganic Chemistry Nomenclature

© Patricio Gómez Lesarri

Inorganic Chemistry

Nomenclature

1.- Elements and valences

2.- Ions 3.- Binary compounds 3.1.- Halides & hydrides 3.2.- Oxides & sulfides 3.3.- Peroxides 4.- Hydroxides 5.- Oxyacids 6.- Oxyanions

Until the XIXth century, each substance had a common name which had nothing to do with its formula. Nowadays, there are more than 9 million of different substances, so using common names to call chemical substances is impossible.

The IUPAC (International Union of Pure and Applied Chemistry)

is an International association founded in 1921 which states the rules of naming and formula writing of the chemical substances. Chemical

Nomenclature is the system which chemists use to name chemical substances. Its aim is that the name of every chemical substance gives us just one chemical formula unambiguously.

1. Elements & oxidation numbers

A chemical element is any simple chemical substance which has just one type of atoms. There are 118 elements, but only 98 elements occur naturally on Earth. All of them are ordered in the Periodic Table according to their atomic number. Each column is called group and has elements of simmilar chemical properties



Oxidation number or valence of an element is the electric charge that the element has when it is combined with others in a compound.

Elements can be classified into 4 types: metals are those elements which usually have a positive valence because they lose electrons. Metals are placed at the left side of the periodic table. On the other hand, nonmetals are the elements which usually have negative valence when combined because they try to gain electrons. They are at the right side of the periodic table. Finally, metalloids are the elements in between, those which have intermediate properties. The last column of elements is composed by noble gases, the most stable elements which are rarely found combined with other elements.

The most common metals have the following oxidation numbers:

Elements Symbol Valence Lithium Li

+ 1

Sodium Na Potassium K Rubidium Rb Caessium (Cesium) Cs Silver Ag Berylllium Be

+ 2

Magnesium Mg Calcium Ca Strontium Sr Barium Ba Zinc Zn Cadmium Cd Boron B + 3 Aluminium Al Copper Cu + 1, + 2 Mercury Hg Gold Au + 1, + 3 Iron Fe

+ 2, + 3 Cobalt Co Nickel Ni Palladium Pd

+ 2, + 4 Platinum Pt Tin Sn Lead Pb Titanium Ti Chromium Cr + 2, + 3, + 6 Tungsten W + 3, + 6 Manganese Mn + 2, + 4, + 6, + 7 Bismuth Bi + 3, + 5



The most frequent nonmetals and metalloids are found in the following table:

Elementos Symbol Valence Hydrogen H +1, -1 Fluorine F - 1 Chlorine Cl

-1, +1, +3, +5, +7 Bromine Br Iodine I Oxygen O - 2, - 1 Sulphur (Sulfur) S

- 2, +2, +4, +6 Selenium Se Tellurium Te Nitrogen N -3, +1, +2, +3, +4, +5 Phosphorus P

-3, +3, +5 Arsenic As Antimony Sb Carbon C + 2, + 4 Silicon Si + 4 Germanium Ge + 4

Assigning oxidation numbers

• The oxidation number of a free element is always zero

• The oxidation number of an monoatomic ion is its own electric charge

• The oxidation number of hydrogen is usually + 1, but in hydrides its oxidation number

equals –1

• The oxidation number of oxygen is usually - 2. Peroxides are exceptions where its

oxidation number equals –1

• The oxidation number of alkali metals (Group 1: Lithium, sodium, potassium, rubidium

and Caessium) and silver is always + 1

• The oxidation number of alkalinearths (Group 2: beryllium, magnesium, calcium,

strontium, barium), zinc and cadmium is always + 2

• The oxidation number of halogens (Group 17: fluorine, chlorine, bromine & iodine) is

always -1 when are combined in binary compounds

• The oxidation number of chalcogens (oxygen family, Group 16: sulphur, selenium, and

tellurium) is always – 2 when are combined in binary compounds

• The sum of oxidation numbers of all the atoms in a neutral compound equals to zero

• The sum of oxidation numbers of all of the atoms in a polyatomic ion equals to the

electric charge on the ion



2. Ions

An ion is an atom or molecule which has electrical charge. There are two kinds of ions: cations and anions. A cation is a positively charged ion. On the other hand, an anion is a negatively charged ion.

Naming cations

• Monovalent cations: cations of elements which have always the same charge have the same name: e.g.: Na+: sodium ion; Al3+: aluminium ion

• Multivalent cations: cations of elements which can take different charges are labeled with a Roman numeral in parenthesis following the cation´s name (Stock System). e. g. Cu*: copper (I) ion; Cu2+: copper (II) ion.

• Some cations have a common name: ammonium, NH4+.

Naming anions

• Monoatomic anions names are formed adding the sufix –ide to the stem of the element Cl (chlorine) ⇒ Cl- : chloride; O: oxygen ⇒ O2- : oxide

• Polyatomic anions: the names of polyatomic anion are formed adding the suffixes –ite and –ate to the stem of the element (see Section 5)

3. Binary compounds

Binary compounds are substances which consist of just two different elements, a cation and an anion.

Writing a formula is very easy: first we write the cation symbol followed by the anion´s.

As we stated in Section 1, binary compounds have no charge because charges of both elements must be balanced. Stoichiometry is the ratio of both elements in the formula, which is shown with subscripts.

• If both charges are the same, the ratio is 1:1: no subscripts are needed • If oxidation numbers are different, use the “criss-cross” method. • Reduce subscripts when possible

Naming binary compounds can be done following these rules:

• Ionic substances

o Monovalent cation: just write the name of the cation, followed by the root of the anion with suffix – ide e.g: KH: potassium hydride

o Multivalent cation: write the name of the cation using Stock system and the name of the anion e.g. FeI3: iron (III) iodide



• Covalent substances

The number of atoms of each element is labeled using a set of preffixes:

Number of atoms Preffix Number of atoms Preffix 2 Di - 5 Penta - 3 Tri - 6 Hexa - 4 Tetra - 7 Hepta -

SF6: sulphur hexafluoride; PCl5: phosphorus pentachloride; As2O3: diarsenic trioxide

3.1 Halides & hydrides These substances consist of fluorine, chlorine, bromine, iodine or hydrogen combined

with other element. The oxidation number of both halogens or hydrogen is -1, so the formula for these substances is AXa, where X represents a halogen or hydrogen and A any other element.

Some combinations of nonmetals and hydrogen have common names:

H2O: water NH3: ammonia or azane

CH4: methane BH3: borane

PH3: phosphane SiH4: silane AsH3: arsane

SbH3: stibane The compounds which consist of hydrogen and halogen or chalcogen act as acids

when they are solved in water. Therefore, these solutions can be named as acids, joining the prefix hydro -, the stem of the element and the suffix – ic, followed by the word acid.

HF Hydrofluoric acid HCl Hydrocloric acid H2S Hydrosulphuric acid HBr Hydrobromic acid H2Se Hydroselenic acid HI Hydroiodic acid H2Te Hydrotelluric acid

3.2 Oxides & sulfides Oxygen and chalcogens take number of oxidation equals to -2, so the formula for these

compounds is A2Xa, where X represents oxygen or a chalcogen and A the other element. However, sometimes the valence of the element is an even number and we have to reduce the subscripts dividing by two, so the formula becomes AXa/2

o Silver oxide: Ag2O; Iron (III) oxide: Fe2O3 o Calcium oxide: Ca2O2 (reducing) ⇒ CaO; Platinum (IV) oxide: Pt2O4 (reducing) ⇒ Pt2O4

3.3 Peroxides

Peroxides are compounds which consist of peroxide ion, O22-, and another element,

usually an alkali metal or alkalinearth. Remember that you cannot reduce the peroxide ion. The formula for these compounds is M2(O2)x.

To name a peroxide first you have to write the name of the cation and, then the peroxide ion. H2O2: hydrogen peroxide; MgO2: magnesium peroxide



© McLean´s Chemistry site http://gohs1.tvusd.k12.ca.us/TeacherWebs/Science/jmaclean/chem2009_2010.htm

4. Hydroxides Hydroxides are compounds which consist of a cation and hydroxide ion, OH-. Their

formula is M(OH)m. Writing the formula is the same as in binary compounds, but

remember that you have to encase the hidroxide ion in parenthesis when needed.

Naming hydroxides is also the same, writing the name of the cation followed by the

word hydroxide: NaOH: sodium hydroxide; Cu(OH)2: copper (II) hydroxide

5. Oxyacids

Oxyacids are compounds which consist of hydrogen, oxygen and a nonmetal element. The general formula is HaXbOc.

For naming acids we use a set of preffixes and suffixes which show the number of

oxygen atoms in the formula.



• If the nonmetal element takes just one oxidation number, the acid is named adding the suffix –ic to the stem of the element e.g: carbonic acid: H2CO3

• If the nonmetal element takes two oxidation numbers, suffixes –ous and –ic are used to distinguish both acids e.g: nitrous acid: HNO2 nitric acid: HNO3

• If nonmetal element takes three oxidation numbers, preffix hypo- and suffixes –ous and –ic are used to distinguish the acids e.g: hyposulphurous acid: H2SO2

• If nonmetal element takes four oxidation numbers, preffixes hypo- and per- and suffixes –ous and –ic are used to distinguish the acids e.g: perchloric acid: HClO4

Preffix/Suffix C N S Cl / Br / I P HYPO - OUS - - H2SO2

Hyposulphurous - HClO

hypochlorous - -

- OUS - HNO2 Nitrous -

H2SO3 Sulphurous -

HClO2 Chlorous -

-

- IC H2CO3 Carbonic acid

HNO3 Nitric -

H2SO4 Sulphuric -

HClO3 Chloric -

H3PO4 Phosphoric -

PER - IC - - - HClO4 Perchloric -

-

6. Oxyanions

Oxyacids in water solution lose protons, H+, so an oxyanion is formed. The valence of the oxyanion is the number of hydrogen atoms lost by the oxyacid.

HNO3 → H+ + NO3- H2SO3 → 2H+ + SO3

2-

To name the oxyanions we have to use different suffixes:

• If the oxyacid has a suffix –ous, we add the suffix –ite to the stem of the nonmetal H2SO3 Sulphurous acid ⇒ SO3

2- Sulphite ion

• If the oxyacid has a suffix –ic, we add the suffix –ate to the stem of the nonmetal HNO3 Nitric acid ⇒ NO3

- Nitrate ion When an oxyanion is combined to a cation, we use the same rules as in binary

compounds: to write the formula, we have to crisscross the valences and reduce the subscripts when possible.

To name these compounds, first we write the name of the cation and then tha anion´s. KClO3: potassium chlorate Fe(NO2)2: iron (II) nitrite Ni2(CO3)3: nickel (III) carbonate

inorganic chemistry nomenclature -...

Documents