@ 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 ..