NCERT Solutions for Class 11 Chemistry Chemistry Part-1 Chapter 3

Classification of Elements and Periodicity in Properties Class 11

Chapter 3 Classification of Elements and Periodicity in Properties Exercise Solutions

<< Previous Chapter 2 : Structure of Atom Next Chapter 4 : Chemical Bonding and Molecular Structure >>

Exercise : Solutions of Questions on Page Number : 92

Q1 :  

What is the basic theme of organisation in the periodic table?


Answer :

The basic theme of organisation of elements in the periodic table is to classify the elements in periods and groups according to their properties. This arrangement makes the study of elements and their compounds simple and systematic. In the periodic table, elements with similar properties are placed in the same group.

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Q2 :  

Which important property did Mendeleev use to classify the elements in his periodic table and did he stick to that?


Answer :

Mendeleev arranged the elements in his periodic table ordered by atomic weight or mass. He arranged the elements in periods and groups in order of their increasing atomic weight. He placed the elements with similar properties in the same group.

However, he did not stick to this arrangement for long. He found out that if the elements were arranged strictly in order of their increasing atomic weights, then some elements did not fit within this scheme of classification.

Therefore, he ignored the order of atomic weights in some cases. For example, the atomic weight of iodine is lower than that of tellurium. Still Mendeleev placed tellurium (in Group VI) before iodine (in Group VII) simply because iodine's properties are so similar tofluorine, chlorine, and bromine.

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Q3 :  

What is the basic difference in approach between the Mendeleev's Periodic Law and the Modern Periodic Law?


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Q4 :  

On the basis of quantum numbers, justify that the sixth period of the periodic table should have 32 elements.


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Q5 :  

In terms of period and group where would you locate the element with Z =114?


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Q6 :  

Write the atomic number of the element present in the third period and seventeenth group of the periodic table.


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Q7 :  

Which element do you think would have been named by

(i) Lawrence Berkeley Laboratory

(ii) Seaborg's group?


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Q8 :  

Why do elements in the same group have similar physical and chemical properties?


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Q9 :  

What does atomic radius and ionic radius really mean to you?


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Q10 :  

How does atomic radius vary in a period and in a group? How do you explain the variation?


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Q11 :  

What do you understand by isoelectronic species? Name a species that will be

isoelectronic with each of the following atoms or ions.

(i) F-

(ii) Ar

(iii) Mg2+

(iv) Rb+


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Q12 :  

Consider the following species:

N3-, O2-, F-, Na+, Mg2+ and Al3+

(a) What is common in them?

(b) Arrange them in the order of increasing ionic radii.


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Q13 :  

Explain why cations are smaller and anions larger in radii than their parent atoms?


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Q14 :  

What is the significance of the terms - 'isolated gaseous atom' and 'ground state' while defining the ionization enthalpy and electron gain enthalpy?

Hint: Requirements for comparison purposes.


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Q15 :  

Energy of an electron in the ground state of the hydrogen atom is -2.18 x 10-18 J. Calculate the ionization enthalpy of atomic hydrogen in terms of J mol-1.


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Q16 :  

Among the second period elements the actual ionization enthalpies are in the

order Li < B < Be < C < O < N < F < Ne.

Explain why

(i) Be has higher ΔiH than B

(ii) O has lower ΔiH than N and F?


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Q17 :  

How would you explain the fact that the first ionization enthalpy of sodium is

lower than that of magnesium but its second ionization enthalpy is higher than

that of magnesium?


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Q18 :  

What are the various factors due to which the ionization enthalpy of the main

group elements tends to decrease down a group?


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Q19 :  

The first ionization enthalpy values (in kJmol-1) of group 13 elements are :

B Al Ga In Tl
801 577 579 558 589

How would you explain this deviation from the general trend?


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Q20 :  

Which of the following pairs of elements would have a more negative electron gain enthalpy?

(i) O or F (ii) F or Cl


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Q21 :  

Would you expect the second electron gain enthalpy of O as positive, more negative or less negative than the first? Justify your answer.


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Q22 :  

What is the basic difference between the terms electron gain enthalpy and electronegativity?


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Q23 :  

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


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Q24 :  

Describe the theory associated with the radius of an atom as it

(a) gains an electron

(b) loses an electron


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Q25 :  

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


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Q26 :  

What are the major differences between metals and non-metals?


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Q27 :  

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.


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Q28 :  

The increasing order of reactivity among group 1 elements is Li < Na < K < Rb <Cs whereas that among group 17 elements is F > CI > Br > I. Explain.


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Q29 :  

Write the general outer electronic configuration of s-, p-, d- and f- block elements.


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Q30 :  

Assign the position of the element having outer electronic configuration

(i) ns2 np4 for n = 3 (ii) (n - 1)d2 ns2 for n = 4, and (iii) (n - 2) f7 (n - 1)d1 ns2 for n = 6, in the periodic table.


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Q31 :  

The first (ΔiH1) and the second (ΔiH) ionization enthalpies (in kJ mol-1) and the (ΔegH) electron gain enthalpy (in kJ mol-1) of a few elements are given below:

Elements ΔiH ΔiH ΔegH
I 520 7300 -60
II 419 3051 -48
III 1681 3374 -328
IV 1008 1846 -295
V 2372 5251 +48
VI 738 1451 -40

Which of the above elements is likely to be :

(a) the least reactive element.

(b) the most reactive metal.

(c) the most reactive non-metal.


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Q32 :  

Predict the formula of the stable binary compounds that would be formed by the combination of the following pairs of elements.

(a) Lithium and oxygen                     (b) Magnesium and nitrogen

(c) Aluminium and iodine                   (d) Silicon and oxygen

(e) Phosphorus and fluorine              (f) Element 71 and fluorine


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Q33 :  

In the modern periodic table, the period indicates the value of:

(a) Atomic number

(b) Atomic mass

(c) Principal quantum number

(d) Azimuthal quantum number.


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Q34 :  

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

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

(b) The d-block has 8 columns, because a maximum of 8 electrons can occupy all the orbitals in a d-subshell.

(c) Each block contains a number of columns equal to the number of electrons that can occupy that subshell.

(d) The block indicates value of azimuthal quantum number (l ) for the last subshell that received electrons in building up the electronic configuration.


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Q35 :  

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?

(a) Valence principal quantum number (n)

(b) Nuclear charge (Z)

(c) Nuclear mass

(d) Number of core electrons.


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Q36 :  

The size of isoelectronic species — F-, Ne and Na+ is affected by

(a) Nuclear charge (Z )

(b) Valence principal quantum number (n)

(c) Electron-electron interaction in the outer orbitals

(d) None of the factors because their size is the same.


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Q37 :  

Which one of the following statements is incorrect in relation to ionization enthalpy?

(a) Ionization enthalpy increases for each successive electron.

(b) The greatest increase in ionization enthalpy is experienced on removal of electron from core noble gas configuration.

(c) End of valence electrons is marked by a big jump in ionization enthalpy.

(d) Removal of electron from orbitals bearing lower n value is easier than from orbital having higher n value.


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Q38 :  

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

(a) B > Al > Mg > K           (b) Al > Mg > B > K

(c) Mg > Al > K > B           (d) K > Mg > Al > B


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Q39 :  

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

(a) B > C > Si > N > F            b) Si > C > B > N > F

(c) F > N > C > B > Si            d) F > N > C > Si > B


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Q40 :  

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

(a) F > Cl > O > N           (b) F > O > Cl > N

(c) Cl > F > O > N           (d) O > F > N > Cl


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<< Previous Chapter 2 : Structure of Atom Next Chapter 4 : Chemical Bonding and Molecular Structure >>

Chemistry Part-1 - Chemistry : CBSE NCERT Exercise Solutions for Class 11th for Classification of Elements and Periodicity in Properties will be available online in PDF book form soon. The solutions are absolutely Free. Soon you will be able to download the solutions.

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