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Thursday, August 5, 2021

Penetration Effect: Penetration Power:

The probability of an electron which allows an electron to get close to the nucleus is known as penetration effect. It is known as the proximity of the electron in the orbital to the nucleus.

(1)  The relative penetration power of sub shells within same shell (same value of n) follow the order as:


We consider it for each shell and sub shell as the relative density of the electrons near the nucleus of atoms. It is clear that the ‘S’ electrons have greater probability of coming closer to the nucleus than the P, d or f electrons of the same principal energy shell. 

(2) For different values of shell (n) and sub shell (l), decreasing penetrating power of an electron follows as:


(3) In other words, ‘S’ electrons penetrate (more nearer) more towards the nucleus than the ‘P’ electrons and the penetrating power of the electrons in the given principal energy shell varies as S> P> d>f. Thus the ‘S’ electrons experience more attraction from the nucleus than the p d or f electrons of the same principal energy shell.

Therefore, greater energy required to remove out electron from‘s’ orbital than ‘p’, d and ‘f’ orbital. Thus the ionization potential for pulling out an ‘s’ electron is maximum  and it decreases in pulling out a p , d or f electron of the same principal energy shell.

(4) Ionization potential or Ionization enthalpy of an atom is directly proportional to penetration power of orbitals.

Application of Penetration effect:

Example: Ionization energy of Boron is smaller than Beryllium even though effective nuclear charge is higher?

Solution: The electronic configurations of Boron and Beryllium are (5B=1S2,2S2,2p1) and (4Be =1S2,2S2).

In Boron the outermost electron is present in the 2p orbital (low penetration power) and is less strongly bound than the electron present in a 2S orbital of Beryllium(Have more penetration power), which will has a higher Zeff. It is easier to ionize the Boron atom.

Related Questions:

(1) What are the Amphoteric metals ? gives Examples.

(2) Name of total metalloids present in periodic table ?

(3) Total numbers of elements which are liquid at normal temperature is ?

(4) What is Mendeleev's periodic table ? give important features and draw back of Mendeleev's table.

(5) What is atomic density ? give the periodicity of atomic density in periods and groups.

(6) What is atomic volume ? and what is periodicity of atomic volume in groups and periods ?

(7) Why there are 2, 8 and 8 elements in first, second and third periodic of periods table respectively ? Explain.

(8) In alkali metal group which is the strongest reducing agent in aqueous solution and why?

(9) The electron affinity of sulphur is greater than oxygen. Why?

(10) The first ionization energy of carbon atom is greater than that of boron atom, whereas reverse is true for the second ionization energy. Explain.

(11) The electronegativities of B, Al, Ga are 2.0, 1.5, 1.6 respectively. The trend is not regular. Explain.

(12) Li2CO3 decomposes on heating but other alkali metal carbonates don’t. Explain.

(13) Of all noble metals, gold has got a relatively high electron affinity. Explain.

(14) What are the increasing order of ioni radii of first group elements in water ?

(15) What are the increasing order of molar conductivity of first group elements in water ?


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