Tag: chemistry

Questions Related to chemistry

Which pair of element has almost identical electronegativity values?

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. $In,Tl$

  2. $B,Al$

  3. $B,Ga$

  4. $Al,Tl$

Show answer
Correct Option: A
Explanation:

Both have close IE and electron affinity values(both are metals) and hence similar electronegativity values.
$Electronegativity=\dfrac{IE+EA}{2}$

Mulliken scale of elecrtonegativity uses the concept of:

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. E. A. and EN of pauling

  2. E.A. and atomic size

  3. E.A. and I.P.

  4. E.A. and bond energy

Show answer
Correct Option: C
Explanation:

Mulliken proposed that the arithmetic mean of the first ionization energy and the electron affinity should be a measure of the tendency of an atom to attract electrons.

If the ionisation potential is IP, electron affinity is EA and electronegativity is x then which of the following relation is correct.

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. 2X-EA-IP=0

  2. 2EA-X-IP=0

  3. 2IP-X-EA=0

  4. All of the above

Show answer
Correct Option: A
Explanation:
Electron affinity: The amount of energy released when an electron is added to the outermost shell of one mole of an isolated gaseous atom in its lower energy state.

Ionisation energy: Minimum energy required to remove most loosly held outer most shell e – in ground state from an isolated gaseous atom is known as ionisation potential.

$\displaystyle X= \frac{IP+EA}{2}$

$2X-IP-EA=0$

Electronegativity of F on Pauling scale is 4.0. Its value on Mulliken scale 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. 12.35

  2. 11.0

  3. 15.2

  4. 14.2

Show answer
Correct Option: A
Explanation:

Electronegativity of F on Pauling scale is 4.0. Its value on Mulliken scale is 11.2
$\displaystyle \chi (Pauling) = 0.34 \chi (Mulliken) -0.2 $
$\displaystyle 4.0 = 0.34\chi (Mulliken) -0.2 $
$\displaystyle \chi (Mulliken) = 12.35 $

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

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

Show answer
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

Show answer
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

Show answer
Correct Option: D

The equation for the preparation of $CH _4$ from anhydrous sodium ethanoate [sodium acetate] is:
$CH _3COONa + NaOH \xrightarrow {CaO/\Delta } CH _4+ Na _2CO _3$

methane study of methane carbon- an important element hydrocarbons chemistry

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

Reaction:
$CH _3COONa + NaOH \xrightarrow {CaO/\Delta } CH _4+ Na _2CO _3$
                                                        methane