JSS 2: COMPOUNDS

A compound is a substance that contains two or more elements that are chemically combined in a fixed ratio. 

Examples of compounds are 

Water (H2O)

Sand (SiO2)

Limestone (CaCO3)

Common salt (NaCl)

Ethanol (C2H5OH)

Caustic soda (NaOH)

Washing soda (Na2CO3.H2O) etc

          Formation of Compounds

Compounds are formed through chemical reactions between elements.

The reaction involves chemical bonds either Ionic (electrovalent) bond or covalent bond.

Example: Hydrogen burns in oxygen to form water.

2H₂ + O₂ → 2H₂O

           Classification of compounds

Chemical compounds can be classified in two major ways:

(I) Classification based on how atoms bond

(II) Classification based on their composition 

(1) Classification based on how atoms bond

I. Ionic (Electrovalent) compounds:

Ionic compounds are formed when atoms transfer electrons, creating charged particles called ions. It usually happens between a metal and a non-metal. The metal loses electrons to form a positively charged ion (cation), and the non-metal gains electrons to become a negatively charged ion (anion). The opposite charges attract and form a strong electrostatic bond.

Examples: 

Sodium chloride (NaCl)

Magnesium oxide (MgO)

Calcium chloride (CaCl2)

Potassium iodide (KI)

II. Covalent compounds 

Covalent compounds form when two or more non-metals share electrons to achieve stability.

Examples:

Water (H2O)

Carbon dioxide (CO2)

Methane (CH4)

Glucose (C6H12O6)

(2). Classification based on their composition

I. Organic compounds 

II. Inorganic compounds

            Organic compounds

Organic compounds primarily contain carbon atoms bonded to hydrogen, and often to oxygen, nitrogen, or other elements. These compounds form the basis of living organisms and are the focus of organic chemistry.

Examples

1. Methane (CH₄)

2. Ethane (C₂H₆) 

3. Ethanol (C₂H₅OH)

4. Methanoic acid (HCOOH)

5. Glucose (C₆H₁₂O₆)

               Inorganic compounds 

Inorganic compounds do not primarily contain carbon-hydrogen bonds. They include salts, metals, minerals, oxides, and acids. Inorganic compounds are mostly found in non-living systems and are studied in inorganic chemistry.

Examples:

Sulphuric acid (H2SO4)

Sodium carbonate (Na2CO3)

Ammonia (NH3)

Calcium carbonate (CaCO3)

         

           Properties of Compounds

1. Compounds have a definite composition.

2. They have unique properties different from their elements.

3. They can only be broken down by chemical means.

4. Compounds have fixed boiling and melting points.

          Separation of Compounds

Compounds can only be broken down by chemical reactions, such as:

I. Electrolysis (e.g., splitting water into hydrogen and oxygen)

II. Heating (e.g., decomposition of calcium carbonate)

Assignment

Explain the following:

I. Organic chemistry 

II. Electrolysis