CLASS :- 11
Ionization enthalpy 👇
The energy required to removal an electron from outer cell are valency cell of isolated gaseous atom in its ground state
Ionization enthalpy is also known as ionization potential
the ionization enthalpies Express in unit of kilojoule per mole electron volt per atom or kilocalorie per mole
Example
Na → Na + + e- △H = +495.8 KJ/mol
Successive ionization enthalpy
The energy required to remove subsequent electron from outer shell or valence shell of an atom in the gaseous state are known as successive ionization enthalpy
the energy required for removal of first electron is called first ionization enthalpy after that the energy required removal of second electron from monovalent cations is called second ionization enthalpy and the removal of third electron from outer cell or valence shell from bi valent cations is called third ionization enthalpy
Example
The successive ionization enthalpy of magnesium
Mg → Mg++ + 2e-
(1) 1st ionization energy, 737.7 kJ⋅mol−1
Mg → Mg+ + e- △iH = +737.7 KJ/mol
First ionization enthalpy is the enthalpy change when most losely bonded electron is removed from valency our outer shell of of an isolated gaseous atom and first ionization enthalpy always less than 2 or third ionization enthalpy
(2) 2nd ionization energy, 1450.7kJ⋅mol−1;
Mg+ → Mg++ + e- △iH = + 1450.7 KJ/mol
Second ionization enthalpy as the energy required to removal of second-most loosely bonded electron from monovalent cations of the element
The second ionization enthalpy always greater than to first ionization enthalpy because after removal of one electron from valency shell atom can be changed monovalent cations , in Monovalent cations the attractions between outer shell electrons and nucleus increases compared to neutral gaseous atom because in outer shell after removal of one electrons , number of electron decrease but effective nuclear charge always constant then attractions between electrons of monovalent cations and nucleus increase then required energy removal of second electrons always more than two first ionization enthalpy
IE2 > IE1
2nd ionization energy, 1st ionization energy,
Of Mg 1450.7kJ⋅mol−1 > of Mg 737.7 kJ⋅mol−1
The successive ionization enthalpy of aluminium
Al → Al+++ + 3e-
(1) 1st ionization energy, 577 kJ⋅mol−1
Al → Al+ + e- △iH = +577 KJ/mol
(2) 2nd ionization energy, 1820 kJ⋅mol−1;
Al+ → Al++ + e- △iH = +1820 KJ/mol
(3) 3rd ionization energy, 2740 kJ⋅mol−1
Al++ → Al+++ + 3e- △iH = +2740 KJ/mol
Factor affecting of ionization enthalpy
(i) size of the atom
Enthalpy decrease with increase in size of an atom because the attractions force would been valency cell electron and in nucleus effective charge decrease as a result it becomes easier to removal of the electron from outer are valency celli
(ii) charge on the nucleus
increase with increase in nuclear charge because the treacherous force the attractions force increase between electron and nucleus when nuclear charge increases the removal of of an electron from isolated atom is difficult task
screening effect of the inner electrons
the The inner electrons always protect outer are valence shell electrons from attractions of nucleus , the protection of outer electrons from attractions of nucleus by the inner electrons is called screening effect or shielding effect
As a result of this outermost electrons does not feel full attraction force from the nucleus that actual attractions felt by an electrons is term as effective nuclear charge
(iii) Penetration effect of electrons
The S atomic orbital small in a size then the Penetration effect is highest compared to p d & f atomic orbital
S- atomic orbital penetrate more than p d & f atomic orbital and come to close of nucleus then the required energy for removal of electrons is always more than p - orbital, p-atomic orbital Penetration effect more than to d-orbital the required energy removal of p- electrons from p-atomic orbital always more than to d- atomic orbital
(iv) Electronic arrangement
it has been observed in periodic table that certain electronic configuration of an atom of the element are more stable than other for example half filled are complete field shell have extra stability associated with them
(according atomic orbital stability S1& s2 , p3& p6, d5& d10, f7& f14)
(1)The noble gas have the most stable electronic configuration ns2 and P6 in each period then the ionization enthalpy highest in in their respected period
(2) the second group are alkaline earth metal have stable outer electronic configuration ns2 then ionization enthalpy is also a large
(3) Nitrogen (1s2 ,2s2 2p3) phosphorus (1s2 ,2s2 2p6,3s2 3p3) atoms of the element have stable outer electronic configuration ns2 and np3 then the required large energy to removal of the electrons
The reason of ionization enthalpy in the periodic table
Verizon along A period👇
In general form the ionization enthalpy increase with increas eatomic number in a period because atomic size decrease and attractions Between outer shell electrons and nucleus increase because gradually one by one Proton inter in nucleus
But some irregularities find out when on moving across a period from left to right
As 👇
Boron (13 group ) ionization enthalpy +801 KJ/mol and beralium (2 group )first ionization enthalpy +899.5 KJ/mol it is less than to beralium first ionization enthalpy because in beralium (1s2 ,2s2 ) stable electronic configuration compare to boron (1s2 ,2s2 2p1) atoms of the element
nitrogen (15 group ) ionization enthalpy +1402.1 KJ/mol and oxygen (16 group ) first ionization enthalpy +1314 KJ/mol it is less than to nitrogen first ionization enthalpy because in Nitrogen (1s2 ,2s2 2p3) stable electronic configuration compare to oxygen (1s2 ,2s2 2p4) atoms of the element
Variation down a group👇
On moving down a group the ionization enthalpy decrease because gradually outer shell number increase means atom size increase then the attraction between outer shell electrons and nucleus decrease
Li △iH = +520 KJ/mol
Na △iH = +496 KJ/mol
K △iH = +419 KJ/mol
Rb △iH = +403 KJ/mol
Cs △iH = +374 KJ/mol
