Class 11 Chemistry Classification of Elements and Periodicity in Properties Question and Answers

Periodicity In Properties Class 11 Questions

Question 1. Would you expect the second electron-gain enthalpy of 0 as positive, more negative, or less negative than the first? Justify your answer.
Answer:

There are several valence electrons in oxygen and it requires two more electrons to complete its octet. So, the O-atom accepts one electron to convert into an O-ion and in the process liberates energy. Thus, the first electron-gain enthalpy of oxygen is negative.

⇒ \(\mathrm{O}(g)+e \rightarrow \mathrm{O}^{-}(g)+141 \mathrm{~kJ} \cdot \mathrm{mol}^{-1}\left(\Delta_i H_1=-v e\right)\)

However, when another electron is added to O- to form 02-ion, energy is absorbed to overcome the strong electrostatic repulsion between the negatively charged O ion and the second incoming electron. Thus, the second electron-gain enthalpy of oxygen is positive.

⇒ \(\mathrm{O}^{-}(\mathrm{g})+e \rightarrow \mathrm{O}^{2-}(\mathrm{g})-\left(780 \mathrm{~kJ} \cdot \mathrm{mol}^{-1}\right)\left(\Delta_i H_2=+v e\right)\)

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Question 2. How would you react to the statement that the electronegativity of N on the Pauling scale is 3.0 in all the nitrogen compounds?
Answer:

The electronegativity of any element depends on the hybridization state and oxidation state of that element in a particular compound, i.e., the electronegativity of an element varies from compound to compound. For example, the electronegativity of Natom varies as sp3 —N < sp2—N < sp—N. So, the, given statement is not correct.

Question 3. Would you expect the first ionisation enthalpies for two isotopes of the same element to be the same or different? Justify your answer.
Answer:

Isotopes of an element have the same number of electrons and similar electronic configurations. So their nuclear charge and atomic radii are identical. Consequently, two isotopes of the same element are expected to have the same ionisation enthalpy.

Question 4. What are the major differences between metals and
non-metals?
Answer:

Metals exhibit a pronounced propensity to lose electrons, resulting in the formation of cations.

• They serve as potent reducing agents, possess low ionization enthalpies, exhibit less negative electron gain enthalpies, have low electronegativity, and generate basic oxides and ionic compounds.
• Non-metals exhibit a pronounced inclination to acquire electrons, resulting in the formation of anions.
• They are potent oxidizing agents, possess elevated ionization enthalpies, exhibit substantial negative electron-gain enthalpies, demonstrate high electronegativity, and generate acidic oxides and covalent compounds.

Class 11 Chemistry Classification of Elements and Periodicity in Properties Question and Answers

Question 5. Use the periodic table to answer the given questions. Identify an element with 5 electrons in an outer subshell. Identify an element that would tend to lose 2 electrons. Identify an element that would tend to gain 2 electrons. Identify the group having metal, non-metal, liquid, and gas at room temperature
Answer:

Fluorine. Its configuration is ls²2s²2p⁵

Magnesium. Its configuration is ls²2s²2p⁶3s². So, Mg loses 2 electrons from its outermost shell to form Mg2+ and attains a stable configuration.

Oxygen. Its configuration is ls²2s²2p⁴ So, O gains 2 electrons to form O₂– and attains stable configuration.

Group-17. The metallic character of astatine (At) is much greater than its non-metallic character and its melting point is very high (3O₂°C).

So, astatine is considered as a metal. So in group-17 there is a metal (At), non-metals (F2, Cl₂, Br₂, I₂), liquid (Br₂) and gas (F₂, Cl₂).

Question 6. The order of reactivity of group-1 LI < Na < K < Rb < Cs whereas that of group-17 elements Is F > Cl > Br >I. Explain.
Answer:

There is only one electron in the valence shell of the elements of group 1. Thus, they have a strong tendency to lose this single electron.

The tendency to lose electrons depends on the ionization enthalpy. As ionization enthalpy decreases down the group, the correct order of increasing reactivity of group-1 elements is Li < Na < K < Rb < Cs. On the other hand, there are 7 electrons in the valence shell of the elements of group-17. Thus, they have a strong tendency to gain a single electron.
The tendency to gain electrons depends on the electrode potentials of the elements. As the electrode potential of elements decreases down the group, the correct order of activity is F > Cl > Br >I.

Class 11 Chemistry Important Questions

Alternate explanation: In the case of halogens, their reactivity increases with the increase in electron-gain enthalpy.

Order of electron-gain enthalpy: F < Cl > Br >I. As electron gain enthalpy decreases from Cl toI, the order of activity also follows this sequence. However, fluorine is the most reactive halogen as its bond dissociation energy is very low.

Class 11 Chemistry Classification of Elements and Periodicity in Properties Question and Answers

Question 7. Assign the position of the element having outer electronic configuration: ns2np4 for n = 3, 0 (n-l)d2ns2 for n = 4 & (n-2)/7(n-l)d1ns2 for tt = 6, in the periodic table.
Answer: (T) As n= 3, the element belongs to the period. Since the last electron enters the p-orbital, the given element is a p-block element. For p-block elements, group no. of the element = 10+no. of electrons in the valence shell.

The element is in the (10+6) = 16th period

As n = 4, the element belongs to the fourth period.

Since is present in the element, it is a block element. For d-block elements, group no. of the element = no. of ns electrons + no. of(n-l) f electrons = 2+2 = 4. Therefore, the element is in the 4th period.

As n – 6, the element belongs to the sixth period. Since, the last electron enters the f-orbital, the element is a f-block element. All f-block elements are situated in the third group of the periodic table.

The first (A1H1) and second (A1H2) ionisation enthalpies (klmol-1) and the (AegH) electrongain enthalpy (in kj.mol-1 ) of a few elements are given below: Which of the above elements is likely to be the P least reactive clement. the most reactive metal.

the most reactive non-metal. the least reactive non-metal. the metal which can form a stable binary halide of the formula MX2(X = halogen).

Elements And Periodicity In Properties Pdf

Question 8. The metal that can form a predominantly stable covalent halide of the formula MX (X = halogen)? Element V is the least reactive metal as it has the highest first ionisation enthalpy & positive electron-gain enthalpy.|
Answer

The element is the most reactive metal due to its lowest initial ionization enthalpy and low negative electron gain enthalpy.

• Element 3 is the most reactive non-metal due to its exceptionally high initial ionization enthalpy and significantly high negative electron uptake enthalpy.
• Element 4 is the least reactive non-metal due to its large negative electron-gain enthalpy and very moderate initial ionization enthalpy.
• Element 4 possesses low first and second ionization enthalpies. The initial ionisation enthalpy of this element exceeds that of the alkali metals. Consequently, the specified element is an alkaline earth metal capable of forming a stable binary halide with the formula MX2.
• The initial ionization enthalpy of elements is low, whereas the subsequent ionization enthalpy is elevated. It is an alkali metal capable of forming stable covalent halides (MX).
• Predict the formulas of the stable binary compounds generated by the following pairs of elements: OLi and O, Mg and N, Al and Si, P and F, and the element with atomic number 71 and F.

Class 11 Chemistry Classification of Elements and Periodicity in Properties Question and Answers

Question 9. In the modern periodic table, period indicates the value of atomic number atomic mass principal quantum number azimuthal quantum number
Answer: Each period in the modern periodic table begins with the filling of a new shell. So, the period indicates the value of a principal quantum number.

Question 10. Which of the following statements related to the modern periodic table is incorrect?

p -block has 6 columns because a maximum of 6 electrons can occupy all the orbitals in a p-shell.

d -block has 8 columns, as a maximum of 8 electrons can occupy all the orbitals in a d -subshell.

Each block contains some columns equal to the number of electrons that can occupy that subshell.

Question 11. Block indicates the value of azimuthal quantum number (l) for the last subshell that received electrons in building up electronic configuration
Answer: The statement is incorrect because d -the block has 10 columns because a maximum of ten electrons can occupy all the orbitals in a d -subshell.

Class 11 Chemistry Periodic Table Notes

Question 12. Anything that influences the valence electrons will affect the chemistry of the element. Which one of the following factors does not affect the valence shell?

1. Valence principal quantum number (n)
2. Nuclear charge (Z)
3. Nuclear mass
4. Number of core electrons.
5. Nuclear mass does not affect the valence shell electrons (such as, and H have similar chemical properties.
6. The size of isoelectronic species F-, Ne, Na+ is affected by: nuclear charge (Z)
7. valence principal quantum number (n)
8. electron-electron interaction in the outer orbitals is one of the factors because their size is the same.
9. The size of isoelectronic species depends on the nuclear charge. As nuclear charge increases, the size of species decreases.
10. electron-electron interaction in the outer orbitals
11. none of the factors because their size is the same.
12. The size of isoelectronic species depends on the nuclear charge. As nuclear charge increases, the size of species decreases.

Question 13. Which one ofthe following statements is incorrect about ionization enthalpy?

1. Ionization enthalpy increases for each successive electron.
2. The greatest increase in ionization enthalpy is experienced in the removal of electrons from the core noble gas configuration.
3. The end of valence electrons is marked by a big jump in ionization enthalpy.
4. Removal of electrons from orbitals with lower n values is easier than from orbitals with higher values.

Answer: This is incorrect as the removal of electrons from orbitals with lower values is more difficult than the removal of electrons from orbitals with higher values. Because in the former case, the electron remains tightly bound as it more closer to the nucleus.

Question 14. Considering the elements B, Al, Mg, and K, the correct order of their metallic character is:

• B > Al > Mg > K
• Mg > Al > K > B
• Al > Mg > B > K
• K > Mg > Al > B

Answer: The statement is correct because across a period from left to right, the metallic character of the elements decreases but down a group, the metallic character increases. Thus, the metallic character of K is the highest, and that of B is the lowest.

Class 11 Chemistry Classification of Elements and Periodicity in Properties Question and Answers

Question 15. Considering the elements B, C, N, F, and Si, the correct order of their non-metallic character is:

• B>C>Si>N>F
• F>N>C>B>Si
• Si>C>B>N>F
• F>N>C>Si>B

Answer: On moving across a period from left to right, the nonmetallic character of the elements increases. Thus, the order of
non-metallic character ofthe given elements: F > N > C > B. However, on moving down a group, the non-metallic character
of elements decreases. Thus, S is more non-metallic than C. Thus, the non-metallic character of the elements follows the
sequence F>N>C>B>Si.

Question 16. For the elements F, Cl, O, and N correct order of their chemical reactivity in terms of oxidizing property is:

• F > Cl > O > N
• Cl > F > O > N
• F > O > Cl > N
• O > F > N > Cl

Answer: Oxidising power increases across a period from left to right. Thus, the order of oxidizing power decreases in the order F > O > N. On moving down a group, oxidizing power decreases. So, F is a stronger oxidizing agent than Cl. Again, O being more electronegative than Cl, O is a stronger oxidizing agent than Cl. Therefore, the overall decreasing order of oxidizing powers F > 0 > Cl > N.