CHEM 1405 - Chapter 6
Language of Chemistry
Classification of Compounds
Inorganic compounds are classified into Ionic Compounds, Molecular Compounds, and Aqueous
acid.
Ionic compounds are made up of cations and anions. They are classified into two
Binary ionic compounds – Contain two elements, a metal and a non metal.( NaCl, KBr)
Ternary ionic compounds – Contain three elements, of which at least one of them is a metal and
a non-metal ( KNO3, Na2SO4)
Molecular compounds contain molecules. They are binary molecular compounds.
Binary molecular compounds contain two elements that are non-metals (CO2, NH3)
Aqueous acid is a solution of an acid in water. They are classified as the following.
Binary acid – Contain hydrogen and a non-metal. (HCl, HBr)
Ternary acid – They are called oxy acids because they contain hydrogen, oxygen, and a nonmetal. ( H2SO4, HNO3)
Molecules
A molecule is an aggregate of two or more atoms of same or different elements combined in a
fixed proportion by mass.
Ions
An ion is an atom or a group of atoms with positive or negative charges.
The losing of electrons forms positive ions. They are also called cations. The gaining of electrons
forms negative ions. They are also called anions.
Electrical charge on ions
Ionic charge is predicted from the group number as follows:
Group number
# of valence electrons
Ion charge
1(IA)
1
1+
2(IIA)
2
2+
13(IIIA)
3
3+
Q: Predict the ionic charge of the following elements:
a. Ca
b. K
c. P
d. S
14(IVA)
4
4+/-
e. Cl
15(VA)
5
3-
f. N
Note! The net electric charge of an ionic compound must be zero
Predicting formulas of ionic compounds
(1) Using net charge approach
i. Aluminum Iodide
ii. Magnesium Nitride
iii. Calcium Oxide
Al3+ x 1 = 3+
Ix 3 = 3-
AlI3
Mg2+ x 3 = 6+
N3- x 2 = 6-
Mg3N2
Ca2+ x 1 = 2+
O2- x 1 = 2-
CaO
16(VIA)
6
2-
g. As
17(VIIA)
7
1-
(2) By Cross over approach
i.
Ca2+
N3-
ii.
K1+
O2-
K2O
iii.
Al3+
N3-
AlN
Ca3N2
Q. Find the formula of the following ionic compounds.
Calcium Fluoride, Sodium Sulfide, Aluminum Chloride, Potassium Bromide,
Barium Nitride.
Naming of ionic compounds
The metal ion (cation, +) is named first, followed by the non-metal ion (anion, -). For naming the cation,
the element’s name is written unchanged. For mono atomic anions, the first part of the element’s name is
combined with the suffix (-ide).
Ex:
KCl
Potassium Chloride
AlN
Aluminum Nitride
CaO
Calcium Oxide
Stock System
This is the modern method of nomenclature of ions with more than one electric charge. In this system, the
charge of the ion is indicated with Roman Numerals.
Ex:
CuCl
Copper (I) Chloride
CuSO4
Copper (II) Sulfate
FeCl3
Iron (III) Chloride
Q: Write the stock system for the following compounds;
a. TiCl3 b. FeCl2
c. HgI2 d. SnCl4 e. ZnO
Polyatomic Ions are the ions containing two or more atoms.
NH4+
Ammonium
CO32- Carbonate
NO3Nitrate
PO43Phosphate
NO2
Nitrite
SO42Sulfate
OH
Hydroxide
CN
Cyanide
C2H3O2- Acetate
HCO3- Hydrogen Carbonate
HSO4Hydrogen Sulfate
Q: Write the formula of the compounds formed by Na+, NH4+ and Ca2+ with the
–ve ions above.
Covalent compounds (molecular compounds.)
These are formed by the mutual sharing of electrons between atoms. Such compounds are
usually formed between the atoms of non-metals.
Naming of Covalent Compounds:
Greek Prefixes are used to indicate the number of atoms.
1- mono
2-di
3 - tri
4 -tetra
6 -hexa
7 - hepta
8 - octa
9 - nona
5 - penta
10 - deca
The first element is named as it is. The second element’s name is altered to accommodate the
suffix (-ide).
N2O
dinitrogen monoxide
CO
carbon monoxide
CO2
carbon dioxide
The prefix “mono” is never used for naming the first element. No prefix is used to indicate the
number of H atoms.
Naming of Acids
An acid is a substance capable of giving H+ ions when dissolved in water (aqueous solution).
They contain one or more ‘H’ atoms and an anionic group. Their name starts with a prefix
‘Hydro’ and ends in a suffix ‘ic’ in the case of anions whose name ends in ‘ide’.
HCl - Hydrochloric Acid
HCN – Hydro cynic Acid
Naming Oxoacids.
Oxoacids contain Hydrogen, Oxygen and a central element.
H2SO4 - Sulfuric acid, HNO3 - Nitric acid, HClO3 - Chloric acid.
There may be two or more oxoacids with same central atom but a different number of ‘O’
atoms. The following rules are observed for naming such acids, starting with the reference acid
whose name ends with ‘ic’.
For example let us take the reference acid, HClO3 - Chloric acid.
 Addition of one ‘O’ atom to the ‘ic’ acid changes the name of acid to include a prefix
‘per’
HClO4 - Perchloric acid.
 Removal of one ‘O’ atom from the ‘ic’ acid changes the name of acid to include a suffix
‘ous’
HClO2 - Chlorous acid.
 Removal of two ‘O’ atom from the ‘ic’ acid changes the name of acid to include a prefix
‘Hypo’ and a suffix ‘ous’
HClO - Hypochlorous acid.
Naming Oxoanions.
 When all the ‘H’ ions are removed from the ‘ic’ acid, the anions name ends with ‘ate’
 When all the ‘H’ ions are removed from the ‘ous’ acid, the anions name ends with ‘ite’
 When all the ‘H’ ions are not removed, the number of H ions present must be indicated in
the name.
Naming of Bases
A base is a substance that yields OH- ions (Hydroxide ions) when dissolved in water.
NaOH - Sodium Hydroxide