Inductive effect :
It is a permanent effect it depends on the neighbouring group.IT can be +I or -I effect , for example if an electron withdrawing group is attached in a carbon chain
then it will pull the electron clouds towards itself,although there is no proper losing or gaining of electrons.
It is temporary effect which takes place betwen two atoms joined by a multiple bond .This occurs at the requirements of the attacking reagent and involves instantaneous transfer of a shared pair of electrons of the multiple bond to one of the linked atoms.
where Z is the attaching specie
There are many molecules whose behavior cannot be explained by a single lewis structure , infact the actual molecule is said to be in resonance with its other resonance hybrid .