Tag: electronic configuration and valency

Questions Related to electronic configuration and valency

Define the relation among the $EN,\,IE\;and\;E.A.$

chemistry classification of elements- the periodic table periodic trends in physical properties properties and trend trends in periodic table electronic configuration and valency electron configuration

  1. $EN=\displaystyle\frac{IE\times EA}{2}$

  2. $EN=IE+EA$

  3. $2EN=IE-EA$

  4. $EN=\displaystyle\frac{IE+EA}{2}$

  5. $EN=\displaystyle\frac{IE-EA}{2}$

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Correct Option: D
Explanation:

The correct relationship is $EN = \dfrac {IE+EA}{2}$
According to mulliken's scale, the electronegatiity is the average value of ionization potential and electron affinity of an atom.

An element $X$ has $IP = 1681$ kJ/mole and $EA =-333$ kJ/mole then its electronegativity is:

chemistry classification of elements- the periodic table periodic trends in physical properties properties and trend trends in periodic table electronic configuration and valency electron configuration

  1. $(1681 + 333) / 544$

  2. $(1681 - 333 )/ 544$

  3. $(1681 + (-333)) / 2$

  4. $\dfrac{208\sqrt{1681+333}}{544}$

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Correct Option: C
Explanation:

Robert S. Mulliken proposed that the arithmetic mean of the first ionization energy ($E i$) and the electron affinity ($E _{ea}$) should be a measure of the tendency of an atom to attract electrons. As this definition is not dependent on an arbitrary relative scale, it has also been termed absolute electronegativity, with the units of kilojoules per mole or electron volts.
                                        <img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/44e7db9c2cb1be249c807e9435c4d11788ea2efc" class="mwe-math-fallback-image-inline" alt="\chi =(E{\rm {i}}+E_{\rm {ea}})/2\,">

The ${ Z } { eff }$ for
3d electron of Cr
4s electron of Cr
3d electron of ${ Cr }^{ 3+ }$
3s electron of ${ Cr }^{ 3+ }$ are _________ respectively.

chemistry classification of elements- the periodic table periodic trends in physical properties properties and trend trends in periodic table electronic configuration and valency electron configuration

  1. 4.6, 2.95, 4.95, 8.05

  2. 4.95, 2.05, 4.6, 8.05

  3. 4.6, 2.95, 5.3, 12.75

  4. none of these

Show answer
Correct Option: C
Explanation:

Cr ${ 1s }^{ 2 }\quad { 2s }^{ 2 }\quad { 2p }^{ 6 }\quad { 3s }^{ 2 }\quad { 3p }^{ 6 }\quad { 3d }^{ 5 }\quad { 4s }^{ 1 }$

${ 24 }^{ - }$
Using later's rule:
for $3de^{ - }\quad { Z } _{ eff }=24-(4\times 0.35)-(18\times 1)=4.6$
for $4se^{ - }\quad { Z } _{ eff }=24-(0\times 0.35)-(13\times 0.85)-(10\times 1)=2.95$
$Cr^{ 3+ }\quad ({ 1s }^{ 2 }\quad { 2s }^{ 2 }\quad { 2p }^{ 6 }\quad { 3s }^{ 2 }\quad { 3p }^{ 6 }\quad { 3d }^{ 3 })$
for $3de^{ - }\quad { Z } _{ eff }=24-(2\times 0.85)-18=5.3$
for $3se^{ - }\quad { Z } _{ eff }=24-(7\times 0.35)-(8\times 0.85)-(2\times 1)=12.75$
                                         ${ s }^{ 1 }p^{ 6 }$           $2({ s }^{ 2 }p^{ 6 })$                    ${ 1s }^{ 2 }$

The $Z _{effective}$ for $He$ is?

chemistry periodicity periodic trends in physical properties properties and trend trends in periodic table electronic configuration and valency electron configuration

  1. 2

  2. 1.7

  3. 1.85

  4. 1.65

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Correct Option: A
Explanation:
The effective nuclear charge experienced by a 1s electron in helium is +1.70.

The effective nuclear charge $Z _{eff}$ is the net positive charge experienced by an electron in a multi-electron atom.

A given electron does not experience a full nuclear charge because the other electrons are sometimes between it and the nucleus and shield it from the nucleus.

The formula for effective nuclear charge is-

$Z _{eff}=Z-S$

where, 
Z is the number of protons in the nucleus, and S is the shielding constant, the average number of electrons between the nucleus and the electron in question.
The American physicist John Slater derived a number of rules to determine the shielding constant.

He found that for electrons in a 1s orbital, the second electron shields the first by 0.30 units.

$Z _{eff}=Z-S=2- 0.30-1.70$

Hence, the correct option is B.


The screening effect of 'd' electrons is : 

chemistry periodicity periodic trends in physical properties properties and trend trends in periodic table electronic configuration and valency electron configuration

  1. much more than s-electrons

  2. equal to s-electrons

  3. equal to p-electrons

  4. much less than s-electrons

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Correct Option: D

An atom of each element has a definite combining capacity called : 

chemistry structure of the atom electronic configuration and valency electron configuration periodic trends in physical properties

  1. valency

  2. affinity

  3. bonding

  4. energy levels

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Correct Option: A
Explanation:

An atom of each element has a definite combining capacity called its valency.

For example Na has electronic configuration 2,8,1 
So, valency is 1 as after losing one electron it will have stable octet.

The electrons present in the outermost shell of an atom are known as :

chemistry structure of the atom electronic configuration and valency electron configuration periodic trends in physical properties

  1. protons

  2. neutrons

  3. octet

  4. valence electrons

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Correct Option: D
Explanation:

The electrons present in the outermost shell of an atom are known as valence electrons.

The valency of nitrogen in nitrogen dioxide is:

chemistry structure of the atom electronic configuration and valency electron configuration periodic trends in physical properties

  1. 1

  2. 2

  3. 3

  4. 4

Show answer
Correct Option: D
Explanation:

$(D)$  $ 4$


$Sol. $  let the valency of nitrogen in be $ x$. 
           valency of oxygen = $ -2 $
          For $NO _2 $ it will be ,
                                $ x + 2 \times(-2) = 0 $
                                 $ x = +4 $
Hence, the valency of nitrogen in $ NO _2$ is $ +4 $. 

Valency of magnesium and oxygen in $MgO$ is:

chemistry structure of the atom electronic configuration and valency electron configuration periodic trends in physical properties

  1. one and one

  2. two and two

  3. one and two

  4. two and one

Show answer
Correct Option: B
Explanation:

Ans. $(B)$ $(two$ $and$ $two)$

This is because magnesium loses two electrons to have an octet and oxygen gains two electrons to have an octet. The final formula of magnesium oxide is ${MgO}$. So, the valencies magnesium and oxygen in $ {MgO}$ are $2$ and $2$ .

Valence electrons are responsible for the chemical properties of an atom.

chemistry what is inside atom electronic configuration and valency electron configuration periodic trends in physical properties

  1. True

  2. False

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Correct Option: A