why the carbon atom can form 1,2 and 3 bonds??

the carbon atom bonded neighbors can occur 3 possibility : 
1. carbon atoms form a single bond
     this happens in the orbital S and called a sigma bond hybrid orbitals SP3 and tetrahedron-shaped   molecule with an angle of 109.5 degrees. This compound is called saturated hydrocarbons 
2. carbon atoms form a double bond
    occurred in the orbital P and is called a pi bond. angle changes due to two orbital P orbitals SP2 parallel to form an angle of 120 degrees
3. carbon atoms form a triple bond
     there are 2 orbitals of P in parallel so as to change the orbital position of the SP to form an angle of 180 degrees planar

carbon atom has four valence electrons with the atomic radius of the price of the smallest in the group IVA. it is easier for the carbon atoms form covalent bonds with other atoms, especially H, O, N, and halogen atoms (F, Cl, Br, I). covalent bonds are formed to meet the octet rule of covalent bonds with a maximum of 4. covalent bond is so strong that the carbon atom is stable. even this carbon atom electronegativity value 2.5 so that it can bind atoms with electronegativity greater or smaller. carbon atom also has the oxidation state ranging from -2 to +4. therefore the carbon atoms were classified as unique.