Chemistry Class 11 NCERT Solutions: Chapter 3 Classification of Elements and Periodicity Part 4

Q: 22. What is the basic difference between the terms electron gain enthalpy and electronegativity?

Answer:

Electron gain enthalpy is the measure of the tendency of an isolated gaseous atom to accept an electron, whereas electronegativity is the measure of the tendency of an atom in chemical compound to attract a shared pair of electrons.

Electron gain enthalpy is the property of an isolated atom and electronegativity is the property of bonded atom.

Electron gain enthalpy has units like KJ/mol & Ev/atom and electronegativity has no units.

Q: 23. How would you react to the statement that the electronegativity of N on Pauling scale is 3.0 in all the nitrogen compounds?

Answer:

Electronegativity of an element is a variable property. It is different in different compounds. Hence, the statement which says that the electronegativity of N on Pauling scale is 3.0 in all nitrogen compounds is incorrect. The electronegativity of Equation is different in Equation

Q: 24 describe the theory associated with the radius of an atom as it

(a) Gains an electron

(b) Loses an electron

Answer:

(a) When an atom gains an electron, its size increases. When an electron is added, the number of electrons goes up by one. This results in an increase in repulsion among the electrons. However, the number of protons remains the same. As a result, the effective nuclear charge of the atom decreases and the radius of the atom increases.

(b) When an atom loses an electron, the number of electrons decreases by one while the nuclear charge remains the same. Therefore, the interelectronic repulsions in the atom decrease. As result, the effective nuclear charge increases. Hence, the radius of the atom decreases.

Q: 25. Would you expect the first ionization enthalpies for two isotopes of the same element to be the same or different? Justify your answer.

Answer;

The ionization enthalpy of an atom depends on the number of electrons and protons (nuclear charge) of that atom. Now, the isotopes of an element have the same number of protons and electrons. Therefore, the first ionization enthalpy for two isotopes of the same element should be the same.

Q: 26. What are the major differences between metals and non-metals?

Answer:

Metals and non-metals

Metals

Equation - Equation

1.

Metals can lose electrons easily.

1.

Non-metal cannot lose electrons easily.

2.

Metals cannot gain electrons easily.

2.

Non-metal can gain electrons easily.

3.

Metals generally form ionic compounds.

3.

Non-metals generally from covalent compounds

4.

Metals oxides are basic in nature.

4.

Non-metallic oxides are acidic in nature.

5.

Metals have low ionization enthalpies.

5.

Non-metals Equation have high ionization enthalpies.

6.

Metals have less negative electron gain enthalpies.

6.

Non-metals have high negative electron gain enthalpies.

7.

Metals are less electronegative. They are rather electropositive elements.

7.

Non-metals are electronegative.

8.

Metals have a high reducing power.

8.

Non-metals have a low reducing power.

Q: 27. Use the periodic table to answer the following questions.

(a) Identify an element with five electrons in the outer subshell.

(b) Identify an element that would tend to lose two electrons.

(c) Identify an element that would tend to gain two electrons.

(d) Identify the group having metal, non-metal, liquid as well as gas at the room temperature.

Answer:

(a) The electronic configuration of an element having 5 electrons in its outermost subshell should be Equation this is the electronic configuration of the halogen group. Thus, the element can be Equation .

(b) An element having two valence electrons will lose two electrons easily to attain the stable noble gas configuration. The general electronic configuration of such an element will be Equation This is the electronic configuration of group 2 elements. The elements present in-group 2 are Equation

(c) An element is likely to gain two electrons if it needs only two electrons to attain the stable noble gas configuration. Thus, the general electronic configuration of such an element should be Equation . This is the electronic configuration of the oxygen family i.e. Equation

(d) Group 17 has metal, non-metal, liquid as well as gas at room temperature.

Q: 28. The increasing order of reactivity among group 1 elements is Li Equation whereas that among group 17 elements is Equation . Explain.

Answer:

The elements present in-group 1 have only 1 valence electron, which they tend to lose. Group 17 elements, on the other hand, need only one electron to attain the noble gas configuration. On moving down group 1, the ionization enthalpies decrease. This means that the energy required to lose the valence electron decreases. Thus, reactivity increases on moving down a group. Thus, the increasing order of reactivity among group 1 elements is as follows:

Equation

In-group 17, as gain electrons decreases down group 17. Thus, reactivity decreases down a group. The electron gain enthalpy of F is less negative than Cl. Still, it is the most reactive halogen. This is because of its low bond dissociation energy. Thus, the decreasing order of reactivity among group 17 elements is as follows:

Equation

Q: 29. Write the general outer electronic configuration of Equation block elements.

Answer:

Equation

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