Carbon and Its Compounds

CONCEPTS

1. Organogens : The elements from which organic life starts are called organogens. Carbon is the backbone of organic life, supported by elements hydrogen, nitrogen and oxygen. 

2. States of carbon : 

(i) Carbon occurs in the free state as diamond, graphite and coal. 

(ii) Carbon occurs in the combined state as carbonates of metals, all kinds of living being, as petroleum and as carbon dioxide. 

3. Covalent bond or Molecular bond or Homopolar bond : A chemical bond formed between two non-metallic elements by the mutual sharing of one or more electron pairs is called a covalent bond. 

4. Single covalent bond : A chemical bond formed between two non-metallic elements by the mutual sharing of one electron pair only, is called a single covalent bond.

5. Double covalent bond : A chemical bond formed between two non-metallic elements by the mutual sharing of two electron pairs, is called a double covalent bond. 

6. Triple covalent bond : A chemical bond formed between two non-metallic elements by the mutual sharing of three electron pairs, is called a triple covalent bond.

7. Covalency : The number of electron pairs which an atom of an element mutually shares with another atom or atoms of the same or different elements, so as to acquire a stable configuration like noble gases, is called covalency. 

8. Covalent compound or Molecular compound : The chemical compound formed as a result of mutual sharing of electron pairs of two or more different kinds of atoms is called a covalent compound. 

9. Non-polar covalent compound : A covalent compound in which the shared pair of electrons are equally distributed between two or more different atoms is called a non-polar covalent compound. For example, methane, ethane, etc. 

10. Polar covalent compound : A covalent compound in which the shared pair of electrons are unequally distributed between the two atoms, is called a polar covalent compound. For example, water, hydrochloric acid, etc. 

11. Properties of covalent (molecular) compounds : 

(i) They have low melting points and boiling points.

(ii) They have low densities, i.e., their density is generally less than that of water. 

(iii) They are generally gaseous or volatile liquids or soft solids. 

(iv) They are insoluble in water, but soluble in organic solvents. 

(v) They are bad conductors of electricity.