does electric impulse convert itself into chemical to cross the synapse and reach to dendrite of other neuron
The electrical signals (nerve impulses) carried by neurons are passed on to other neurons at junctions called synapses.
The signal may be directly transferred at electrical synapses or, if there is no physical link between adjacent neurons, the signal is carried across the gap by chemicals called neurotransmitters.
There is an electrical difference between the inside of the axon and its surroundings, like a tiny battery. When the nerve is activated, there is a sudden change in the voltage across the wall of the axon, caused by the movement of ions in and out of the neuron. This triggers a wave of electrical activity that passes from the cell body along the length of the axon to the synapse.
So, basically, Electrical events propagate a signal within a neuron, and chemical processes transmit the signal from one neuron to another or to a muscle cell.