Carbon and Its Compounds

• The atmosphere has only 0.03% of carbon dioxide.
• The number of electrons lost or gained by an atom to complete its octet (or duplet) is called its valency. It depends on the number of valence electrons.
• The tendency to attain a completely filled outermost shell (i.e. noble gas configuration) by gaining or losing electrons is called reactivity.
• The shared pair of electrons belongs to the outer shells of both the atoms so as to attain noble gas configuration.
• The simplest molecule formed by sharing of electrons is hydrogen.
• The bonds which are formed by sharing of electrons between two atoms are known as covalent bonds.
• The compounds which are formed by sharing of electrons pair between two atoms are known as covalent compounds. E.g. CH₄, H₂, O₂, etc.
• The melting and boiling points of covalent compounds are low because their intermolecular forces are weak and less amount of energy is required to overcome these forces.
• The covalent compounds are generally poor conductors of electricity because the electrons are shared between atoms and no charged particles are formed in their solution.
• Carbon has three allotropes – graphite, diamond and Buckminster Fullerene.
• When a hydrogen atom is removed from an alkane, the group obtained is called an alkyl group.
• Saturated carbon compounds are usually not very reactive because the carbon-carbon single bonds are very strong.
• Unsaturated carbon compounds are very reactive than saturated carbon compounds.

Uses of graphite

1. It is used in lead pencils as it is soft and leaves black mark on the paper.
   
2. It, being a good conductor of electricity, is used in making electrode in the cells.
   
3. Powdered graphite is used as lubricant because it is very soft and can withstand at high temperature.
   

Uses of diamond

1. It is used in pencils for cutting glass etc because it is the hardest substance known.
   
2. It is used for making dies for drawing thin wires.
   
3. It is used in surgical tools.
   
4. It is used for making jewellery because of high refractive index.
   

Heteroatom In hydrocarbons, the elements like halogen, oxygen, etc replacing hydrogen is called heteroatom. They are also present in some groups.

Graphite	Diamond
Graphite has two dimensional structure oft and greasy. It is a good conductor of heat and electricity. It is grayish black substance.	Diamond is a three dimensional structure. It is the hardest substance known. It is the bad conductor of electricity but good conductor of heat. It is transparent.