Question

Suppose that the carbon atom pictured here as a reactant had already formed a double bond with another carbon atom. how many hydrogen atoms would now be required to fill the carbons outer shell? bond formation between carbon and hydrogen to form methane. suppose that the carbon atom pictured here as a reactant had already formed a double bond with another carbon atom. how many hydrogen atoms would now be required to fill the carbons outer shell? bond formation between carbon and hydrogen to form methane. one two three four

Answer 1

C has a valency of four. C can form 4 covalent bonds.  

The electron configuration of C:

1s²2s²2p²

When C already forms a double bond with another C atom, each of the two C atoms can form only 2 new covalent bonds. This is illustrated by the example below:

H₂C=CH₂

The molecule is an alkene called ethene.  

Answer 2

A carbon atom is capable of bonding with 4 atoms including carbon itself. So, when there is a double bond between two carbon atoms, each carbon atom has an extra 2 unoccupied bonds. Thus, each carbon atom in a C=C bond is capable of bonding with two other hydrogen atoms.