Definition of Compound in Chemistry | Types, Characteristics and Examples

Definition of compound in chemistry

A compound is material consists of two or more elements combined chemically in a fixed ratio. The combining elements lose their chemical properties and cannot be separated by simple physical methods.

For example, 2 atoms of hydrogen and 1 atom of oxygen combine chemically to form water (H20) which has different characteristics than combining elements. Similarly, 2 carbon atoms and one oxygen atom combine to form carbon dioxide.

Characteristics of a compound

Some distinguishing characteristics of compounds are:

1. The constituents of a compound are combined by a chemical reaction.
2. The constituents of a compound lose their chemical properties.
3. Simple physical methods cannot be used to separate the constituents of a compound.
4. A compound contains a fixed ratio of combining elements.
5. Compounds are always homogenous.
6. The composition of combining elements can be expressed in the form of a chemical formula.
7. Changes in energy take place during the formation of a compound.
8. Compounds have fixed boiling and melting points.

Examples of compounds

Some examples of compounds and their combining elements are given below:

Compound	Formula	Constituents
Water	H20	2 hydrogen and 1 oxygen atoms
Sodium chloride	NaCl	1 sodium and 1 chlorine atoms
Carbon dioxide	CO2	1 carbon and 2 oxygen atoms
Ammonia	NH3	1 nitrogen and 3 hydrogen atoms
Sulphuric acid	H2SO4	2 hydrogen, 1 sulphur, and 4 oxygen atoms
Sodium hydroxide	NaOH	1 Sodium, 1 oxygen, and 1 hydrogen atoms
Calcium carbonate	CaCO2	1 calcium, 1 carbon, and 2 oxygen atoms
Sugar	C12H22O11	12 carbon, 22 hydrogen, and 11 oxygen atoms

Types of compounds

Compounds can be divided into three categories:

1. Ionic compounds
2. Covalent compounds
3. Metallic compounds

1. Ionic compound

Ionic compounds are formed by ionic bonding between positively charged ion (cation) and negatively charged ion (anion). Independent forms of the ionic compound do not exist, instead, they are present in the form of crystal. Ionic compounds are neutral having no charge.

As the ionic compounds are formed by the attraction of oppositely charged ions, they have high boiling and melting points. Ionic compounds are represented by the formula unit. The formula unit represents the simplest ratio of combining ions. 

NaCl (sodium chloride), NaBr (sodium bromide), KBr (potassium bromide), CuSO4 (copper sulphate) and NaI (sodium iodide) are some examples of ionic compounds.

2. Covalent compounds

Covalent compounds are formed by covalent bonding in which a pair of an electron is shared between atoms. Covalent compounds do not have any charge and are neutral.

Covalent compounds generally occur in molecular form and constituents of compounds are represented by the molecular formula. The molecular formula represents the number of each atom of an element present in a covalent compound. 

For example, the molecular formula of water, methane, hydrochloric acid are H2O, CH4, and HCL, respectively.

3. Metallic compounds

Metallic compounds are formed by metallic bonding between a metal ion and a nonmetal anion or among metal ions. Metallic compounds are good conductors of heat and electricity. They have very high boiling and melting points. 

An example of metallic compounds is AgNO3 (silver nitrate) that is made up of silver (Ag) metal and nitrate group. CaCl2 (calcium chloride) and Al2S3 (aluminum sulfide) are also metallic compounds.

Some Answers and questions

1. Give 5 examples of compounds.

A. water, sodium chloride, sugar, methane, and hydrochloric acid are examples of compounds.

2. What are the three types of compounds?

A. Ionic, covalent and metallic compounds are three types of compounds.

3. Is an alloy a mixture or a compound?

A. Alloy is a mixture. In alloy, substances are not combined by any chemical reaction but are mixed physically.

4. Is water a compound?

A. Yes, hydrogen and oxygen combine chemically to form water.