9 nomenclature of inorganic compounds

Nomenclature of Inorganic Compounds

Overview

• A lot of compounds are available nowadays.

• Remembering their names would be quite difficult.

• There must be a systematic method of naming (a technique that provides relationship of names with its formula) should be used.

Chemical formula

• It is a representation, which is used to denote one molecule of pure substance

Chemical formula

• It indicates the relative amount of atoms of each element in a molecule, which consists of symbols of the elements composing the pure substance and subscripts denoting relative number of atoms of each element in a unit particle or molecule of the element of compound.

OXIDATION NUMBERS

• Oxidation number or oxidation state is an apparent charge of an atom in a compound when electrons are transferred from one atom to another to form ions.

OXIDATION NUMBERS

• This set of whole numbers (sometimes positive and in other cases, negative) are very useful for predicting the formulas of the compounds, classifying them, comparing the chemical properties of the elements and describing chemical reactions

Rules for Assigning Oxidation Numbers/States 1. The oxidation numbers of an

element in the free or uncombined state is always zero.

• Example: Cu0, Si0, Mg0

Rules for Assigning Oxidation Numbers/States 2. The oxidation numbers of

monoatomic ion is the same as the charge on the ion.

• The group of numbers in the periodic table will help us remember the oxidation numbers.

Rules for Assigning Oxidation Numbers/States • There are two important general

observations:– A common oxidation number of all

metals is positive and is equal to its group number.

– A common oxidation number of all nonmetals is negative and is equal to the group number minus 8.

Common Oxidation States of Common Elements

GROUP NO.

OXIDATION NUMBERS

EXAMPLES

IA +1 Na+, Li+, Ag+1

IIA +2 Mg2+, Ba2+, Zn2+

IIIA +3 Al3+, B3+

IVA +4/-4 C4+

VA -3 N3-, C4-, Si4+

VIA -2 O2-

VIIA -1 F-, Cl-

Notes

• An element with positive oxidation number is a positive ion called CATION and an element with negative oxidation number is a negative ion called ANION.

Notes

• There are elements that have more than one oxidation numbers.

• Generally, they are the transition elements.

Common Oxidation Numbers of Common Transition Elements

OXID NO.

FORMULA NAME OF THE ION

OXID NO.

FORMULA NAME OF THE ION

Cr2+ chromous/chromium (II) Cu2+ cupric/copper (II)

Cr3+ chromic/chromium (III) Hg+ mercurous/mercury (I)

Mn2+ manganous/manganese (II)

Hg2+ mercuric/mercury (II)

Mn4+ manganic/manganese (IV)

Sn2+ stannous/tin(II)

Fe2+ ferrous/iron (II) Sn4+ stannic/tin (IV)

Fe3+ ferric/iron (III) Pb2+ plumbous/lead (II)

Co2+ cobaltous/cobalt (II) Pb4+ plumbic/lead (IV)

Co3+ cobaltic/cobalt (III) H+ hydrogen/hydronium

Cu+ cuprous/copper (I) H- hydride*H is not a transition element.

Rules for Assigning Oxidation Numbers/States 3. The algebraic sum of the oxidation

numbers for all the atoms in the formula of a compound is zero.

ex. Mg2+Br2-

+2 + (-1)(2) = 0

Rules for Assigning Oxidation Numbers/States 4. The sum of the oxidation numbers

of the atoms in a polyatomic ion must be equal the charge of the ion.

Common Polyatomic Ions

Monovalent IonsNH4

+ Ammonium HCO3- Bicarbonate

C2H3O2- Acetate NO2

- Nitrite

ClO- Hypochlorite NO3- Nitrate

ClO2- Chlorite MnO4

- Permanganate

ClO3- Chlorate HSO4

- Bisulfate

ClO4- Perchlorate HSO3

- Bisulfite

CN- Cyanide CNO- Cyanate OH- Hydroxide CNS- Thiocyanate

Common Polyatomic Ions

Divalent IonsCO3

2- Carbonate SO42- Sulfate

CrO42- Chromate S2O3

2- Thiosulfate

Cr2O72- Dichromate HPO4

2- Biphosphate

C2O42- Oxalate SiO3

2- Silicate

SO32- Sulfite ZnO2

2- Zincate

Common Polyatomic Ions

Trivalent IonsPO3

3- Phosphite

PO43- Phosphate

Polyvalent IonsP2O7

4- Pyrophosphate

Rules for Assigning Oxidation Numbers/States

5. Some common oxidation numbers:

– Hydrogen has usually +1, except in hydrides (ionic compounds with IA and IIA), it has –1.

– Oxygen has usually –2, except in peroxides, such as H2O2, and Na2O2, it has –1.

– Aluminum (Group IIIA) has +3: Zinc (Group IIB) has +2 and Silver (Group IB) has +1.

Rule in Writing Formulas

General Method

• The symbol of the cation is written first followed by the symbol of the anion then apply the criss-cross method.

Rule in Writing Formulas

• Metals, nonmetals and inert gases have their formulas the same as their symbols.

Example: Calcium CaMagnesium Mg

Rule in Writing Formulas

• Active gaseous elements are written correctly by taking two atoms of the elements since these are diatomic molecules.

Examples: Oxygen O2

Hydrogen H2

Rule in Writing Formulas

• Compounds: Write the symbol of the positive element or positive radical with their oxidation number first, then followed by the negative element or negative radical with their oxidation number also. The algebraic sum of the oxidation numbers must be equal zero so that the compound will be neutral.

Rule in Writing Formulas

• When the positive oxidation numbers and the negative oxidation numbers are the same, the formula is the same as it stands.

Example: K+Br- KBrSr+2O-2 SrO

Rule in Writing Formulas

• When the positive oxidation number and the negative oxidation numbers are not the same, apply the criss-cross rule so that the algebraic sum of the oxidation numbers will be equal to zero.

Example: Al+3S-2 Al2S3

Ca+2Cl- CaCl2

Rule in Writing Formulas

• Whenever a radical in a formula is taken more than once, enclose the radical inside a parenthesis and write the correct subscript after the parenthesis.

Example: K+(Cr2O7)2- K2Cr2O7

Ba+2(OH)-

Ba(OH)2

Examples

• Sodium chloride• Ferrous oxide• Aluminum iodide• Calcium phosphate• Ammonium carbonate

Systematic Naming of Compounds• Binary Compounds• compound which is composed of two

elements

Binary Salts (M + NM)

• For metals with fixed oxidation no.• Rule: name the (+) ion + name

the stem of (-) ion + IDENaI Sodium iodideMgBr2 Magnesium

bromideK3N Potassium nitride

CaO Calcium Oxide

Binary Salts (M + NM)

• For metals with variable oxidation nos.

•  Method I: Old or Classical Method

•  Rule : name the metal with suffixes –ous or –ic + name of non-metal + IDE

Cu3B Cuprous boride

SnS2 Stannic sulfide

Binary Salts (M + NM)

• For metals with variable oxidation nos.• Method II : Stock or Roman Numeral

Method• Rule : name of metal + (Roman

numeral of the oxid no) + Name of stem of non-metal + IDE

PbBr2 Lead (II) bromide

AuCl3 Gold (III) chloride

Binary Acids (H + NM)

• Dry form (when acid is not dissolved in water)

• Rule: Hydrogen + name of non-metallic element + IDE

HCl Hydrogen chlorideHBr Hydrogen bromide

Binary Acids (H + NM)

• Aqueous Form (when acid is dissolved in water to form an acidic solution)

•  Rule: Hydro + name of the non-metal with suffix –ic + acid

HCl(aq) Hydrochloric acid

HBr(aq) Hydrobromic acid

Non-metal + Non-metal

• Greek prefixes are used to indicate the number of atoms in each element present in a molecule of a compound

• Numeric Prefixes1 - mono 4 - tetra 7 - hepta 10 - deca2 - di 5 - penta 8 - octa 11 - undeca3 - tri 6 - hexa 9 - nona 12 - dodeca

Non-metal + Non-metal

• Rule:• Name the more positive element first

and followed by the name of the more negative element

• Use the Greek prefixes listed above, to indicate the number of atoms of each type of element present in the formula of the compound.

Non-metal + Non-metal

• Rule:• The prefix -MONO is often omitted when it

applies to the first element in a compound.• Use the suffix -IDE to the second element.

N2O dinitrogen monoxide

CO carbon monoxide

SO2 sulfur dioxide

CO2 carbon dioxide

Hydrides

• Hydrogen reacts with many metals to form binary compounds called hydrides.

• In these compounds, the hydrogen is more electronegative than the metal and it is assigned an oxidation number of –1.

• Rule: name the metal + hydrideRbH Rubidium hydrideCsH Cesium hydrideLiH Lithium hydride

Systematic Naming of Compounds• Ternary Compounds• compound which is composed of

three or more elements

Ternary Acids or Oxy-Acids

• Dry form• Rule: Hydrogen + Oxy-ion in –ATE form

H2CO3 Hydrogen carbonate

H3PO4 Hydrogen phosphate

• Rule: Hydrogen + Oxy-ion in –ITE formH2SO3 Hydrogen sulfite

H3PO3 Hydrogen phosphite

Ternary Acids or Oxy-Acids

• Aqueous form• The negative ion is in the form of suffix

–ATE• Rule: name the root of the middle

element + IC plus the word acidH2CO3(aq) Carbonic acid

• The negative ion is in the form of suffix –ITE

• Rule: name the root of the middle element + OUS plus the word acid

H2SO3(aq) Sulfurous acid

Ternary Salts

• Salts of the oxy-acids (Metal + Oxy-ion) 

• Metals with fixed oxidation number.

• Rule: name the metal or (+) ion + name of the negative (-) ion

NaNO3 Sodium nitrate

NaNO2 Sodium nitrite

Ternary Salts

• Salts of the oxy-acids (Metal + Oxy-ion) • Metals with fixed oxidation number.

• Metals with variable oxidation numbers• Rule: name the metal or positive ion

(Roman numeral) + name of the negative ion.

FeCO3 Iron (II) carbonate