@ deva 
ionisation energy or ionisation enthalpy is the enrgy required to remove the most loosely bound electron from an isolated gaseous atom . 
and IE1 , IE2 , these are the removal of first as well as second electron from an atom . 
and the notation that u have given is wrong , 
the second ionisation energy is always more than that of first ionisation energy . 
beacuse , once a atom looses one electron , then it will trying to make it more stable , so, the force that nucleaus exert on outer shell electron will be increased , in that case we have to apply more force for removing the 2nd electron . 
FACTORS AFFECTING IE 
1- atomic radius , 2- nuclear charge 3- orbital penetration 
4- sheilding or screening effect       5- electron pairing within a subshell . 
HOPE IT CLEARS NOW 
ALL THE BEST ..
						

							
ionisation energy or Ionisation enthalpy is the enrgy required to remove the most loosely bound electron from an isolated gaseous atom and IE1, IE2, these are the removal of first as well as second electron from an atomThe notation that you have given is wrong, the second ionisation energy is always more than that of first ionisation energy beacuse once a atom looses one electron, then it will trying to make it more stable, so, the force that nucleaus exert on outer shell electron will be increased, in that case we have to apply more force for removing the 2ndelectron .FACTORS AFFECTING IE1- atomic radius,2- nuclear charge3- orbital penetration4- sheilding or screening effect5- electron pairing within a subshel