Compounds

• A compound is a substance made up of two or more elements chemically combined in a fixed proportion by mass.

For example water (H₂O) is a compound made up of two elements, hydrogen and oxygen.

Hydrogen and oxygen are present in the ratio of 2: 16 or 1: 8 by mass. In pure form of water form any source the two elements are present in same fixed ratio i.e. 1 : 8 by mass.

Types of Compounds:

• The compounds are classified into two types based on the source of origin. These are:
• Inorganic compounds
• Organic compounds

Inorganic compounds:

• These compounds are obtained from non-living sources such as rocks and minerals.

Example:

• Common salt, Marble, Washing soda, Baking soda, Carbon dioxide, Ammonia, Nitric acid, Hydrochloric acid

Organic compounds:

• The organic compounds are the compounds obtained from living beings i.e., plants and animals
• All the organic compounds contain carbon as their essential constituent. The organic compounds are quite often known as carbon compounds.

Example:

• cooking gas, ethane, acetone, alcohol, acetic acid, Sugar, protein, oil
• Compounds are also classified based upon their characteristics as:

1. Acids

2. Bases

3. Salts

• Example of acids:

Sulphuric acid, Hydrochloric acid, Nitric acid, Carbonic acid etc

• Example of bases:

Sodium hydroxide, Potassium hydroxide, Calcium hydroxide, Magnesium hydroxide etc

• Example of salts:

Salts are generally formed by chemical chemical combination of acids and bases dissolved in water.

• Sodium hydroxide + Hydrochloric acid  Sodium chloride + Water
• Sodium chloride, Calcium nitrate, Zinc sulphate etc

Characteristics of Compounds:

A pure compound is composed of the same elements irrespective of the source

• In a compound the same elements are always present in fixed ration by mass irrespective of the source.

For example-

• In carbon dioxide, two elements carbon and oxygen are present in the ratio of 3: 8 by mass.

A pure compound is homogenous in nature

A chemical compound is formed by the chemical reaction between the constituent elements

For example:

Properties of compounds are altogether different from the constituent elements

• A compound is formed as a result of chemical reaction between the elements. Water formed by the reaction between Hydrogen and Oxygen has different properties.
• Water is a liquid whereas hydrogen and oxygen is a gas.
• Hydrogen gas is combustible and Oxygen gas is a supporter of combustion but water is neither combustible nor supports combustion.
• Water stops combustion and is used as fire extinguisher.

Constituents of chemical compounds cannot be separated by physical methods of separation

• Hydrogen and oxygen gas can be separated from water by passing electric current (electrolysis). It cannot be separated by mechanical methods like filtration, distillation etc.

Example:

• When the mixture of iron filings and sulphur powder is heated, a black compound known as iron sulphide (FeS) is formed.
• Compound cannot be separated into its components by physical methods.

Iron filings can be separated from the mixture of iron filings and sulphur by a magnet but iron cannot be separated from iron sulphide by a magnet.

Energy is either released or absorbed during the preparation of a compound.