state the modern periodic law. What is ionization energy ? explain why does ionization energy increases from left to right in a period but decreases from top to bottom in a group ?
Answers
The least energy required to eject the electron from the outermost orbit is termed as ionisation energy.
As we move along the period the number of electron increases bt the sheilding effect of inner electrons remain constant therefore the outer electrons are held tightly and more energy is required to eject them . Though there are 2 exeptions.
1. Be has fully filled configuration so is more stable and more energy is required therefore has more ionisation energy than boron.
2. N has exactly half filled configuration and again is more stable so has more ionistation enegy than oxygen.
Now it decreases from top to bottom because with the increase in nuclear charge there is also increase in atomic size which is more than increase in nuclear charge. Therefore the outermost electron gets loosely held as move move down the group and ionisation enegy decreases.
MORDERN PERIODIC LAW - the physical and chemical properties of the elements are periodic functions of their atomic numbers.