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Some Important Questions

 sanjiv %2811%29

1. How does electronegativity differ from electron affinity? Arrange the following in the order of increasing electronegativity: M, M-M .
Ans: Electronegativity and electron affinity differs from each other in the following ways:

ElectronegativityElectron Affinity
  • It is the tendency of an atom of element to attract bond pairs of electrons towards itself.
  • It is amount of energy released when an isolated gaseous state atom gain an electron.
  • It is applied only to a single atom.
  • It is either applied to an atom or a molecule.
  • Electronegativity is qualitative.
  • It is quantative.

According to increasing electronegativity: M- < M < M+ 

2. Sodium and Mg+ ion have same number of electrons but removal of electron from Mg+ requires more energy than sodium. Explain. 

Ans: Though sodium and Mg+ ion have same number of electrons the atomic size of Mg+ is smaller than Na. Since, smaller the size, the greater is the nuclear force of attraction for valance electrons due to which removal of electron from Mg+ requires more energy than sodium.

3. 
Which of the following electronic configuration would you expect to have the lowest ionization energy and why?
a)1S2, 2S2, 2P6
b) 1S2, 2S2, 2P5
c) 1S2, 2S2, 2P6,3S1
Ans: As we know the elements having half-filled and full filled electronic configuration are stable and they need more energy to move the electron and have higher ionization energy. So, (a) and (c) have higher ionization energy because they have fulfilled and half-filled electronic configuration respectively and (b) has lowest ionization energy due to having unstable electronic configuration.

4. 
Size of the cation is smaller than the size of parent atom. Explain.
Ans: Size of cation is smaller than the size of parent atom because as parent atom loses electron and form cation where number of proton becomes more than number of electron and attractive force increases so radius decreases.

5.
 Size of the anion is larger than the size of parent atom. Explain.
Ans: The size of anion is larger than the size of parent atom because anions are formed due to gain of electrons. When the electrons increases, there are still the same number of protons. This causes the electrons to not be bound tightly to the nucleus like earlier and results in an increase atomic size.


6. 
Electron gain enthalpy of fluorine is unexpectedly less than that of chlorine. Give reason. 
Ans: Fluorine has very small atomic size so there is more inter electronic repulsion. But chlorine has larger size and repulsion between the electron of chlorine is very less. Hence, it can easily gain electron but fluorine can't. So electron gain enthalpy of fluorine is unexpectedly less than of chlorine.


7. State modern periodic law. Why is modern table superior to Mendeleev's periodic table?

Ans: Modern periodic law states that, " The physical and chemical properties of elements are the periodic function of their atomic numbers."

Modern periodic table does correct the defects of Mendeleev's Periodic table. It is based on atomic number which is a more fundamental property of the atom. It removes the anomaly about the position of isotopes in the Mendeleev's periodic table. It also removes the other anomalies found in Mendeleev's periodic table like grouping of chemically dissimilar elements and separations of similar elements.

8. A student reported that the radii of Cu, Cu+ and Cu++ are 96 pm, 122 pm and 72 pm respectively. Do you agree with the reported values? Justify the answer.
Ans: No, I don't agree with reported values. The measurement is made wrongly. More the positive charge more will be the nuclear attraction and outermost electron is more attracted towards the nucleus and the atomic radius is less. So Cu++ < Cu+ < Cu should be the order. But the measurement shows Cu+ > Cu > Cu++  which can not be true.


9. 
Electron affinity of alkaline earth metal and noble gases are almost equivalent to zero. why?
Ans: Since alkaline earth metal and noble gases are stable elements due to having full or half filled electronic configuration. So, they can't easily gain any electron. Therefore their electron affinity are almost equivalent to zero.

10. Define isoelectronic species.
Ans: Isoelectronic species are the
 atoms or ions that have same number of electrons.