No I.E . decrease from (sn) to (pb) due to increase in size of atom & decrease effective nuclear charge

Reason for Increase in Ionization Enthalpy from Tin (Sn) to Lead (Pb)

Introduction:
Ionization enthalpy is the energy required to remove an electron from an atom or a positive ion. It is influenced by various factors such as atomic size, nuclear charge, and electron-electron repulsion. In the case of tin (Sn) and lead (Pb), the ionization enthalpy increases from tin to lead due to the following reasons:

1. Increasing Nuclear Charge:
As we move across a period in the periodic table, the nuclear charge increases. Tin and lead are located in the same period (period 5), but lead has a higher atomic number than tin. The increase in nuclear charge leads to a stronger attraction between the nucleus and the electrons, making it more difficult to remove an electron. Therefore, ionization enthalpy increases from tin to lead.

2. Shielding Effect:
The shielding effect refers to the repulsion between electrons in different energy levels. As we move across a period, the number of electrons in the outermost shell remains the same, but the number of inner shells increases. This increased shielding effect reduces the effective nuclear charge experienced by the outermost electrons. In the case of tin and lead, the shielding effect in lead is greater due to the presence of additional inner shells. As a result, the attractive force between the nucleus and the outermost electron is weakened, requiring more energy to remove the electron. Hence, the ionization enthalpy increases.

3. Electron-Electron Repulsion:
As the atomic number increases, the number of electrons also increases. This leads to an increase in electron-electron repulsion. In the case of lead, the repulsion between the electrons is stronger compared to tin due to the larger number of electrons. This repulsion makes it more difficult to remove an electron, resulting in a higher ionization enthalpy.

Conclusion:
In conclusion, the ionization enthalpy increases from tin (Sn) to lead (Pb) due to the increasing nuclear charge, shielding effect, and electron-electron repulsion. The stronger attraction between the nucleus and the electrons, combined with the increased shielding effect and electron repulsion, makes it more difficult to remove an electron from lead compared to tin.