One app for all your study abroad needs
In this chapter, you have become familiar with the key concepts of the periodic classification of elements, the development of the modern periodic table, the significance of atomic number, periodic trends in physical and chemical properties such as atomic and ionic radii, ionization enthalpy, electron gain enthalpy, electronegativity, valency, oxidation states, and the anomalous behaviour of second-period elements. This blog will provide you with exercises along with their solutions, which will help you understand the concepts more simply.
Contents
Explore Notes of Class 11 Chemistry
NCERT Solutions Class 11 Chemistry (Part-1) Chapter 3: Classification of Elements and Periodicity in Properties
Below, we have provided you with exercises mentioned in the NCERT Class 11 Chemistry (Part-1) Chapter 3: Classification of elements and periodicity in properties.
Exercises
- What is the basic theme of organisation in the periodic table?
- Which important property did Mendeleev use to classify the elements in his periodic table, and did he stick to that?
- What is the basic difference in approach between Mendeleev’s Periodic Law and the Modern Periodic Law?
- On the basis of quantum numbers, justify that the sixth period of the periodic table should have 32 elements.
- In terms of period and group, where would you locate the element with Z =114?
- Write the atomic number of the element present in the third period and seventeenth group of the periodic table.
- Which element do you think would have been named by (i) Lawrence Berkeley Laboratory (ii) Seaborg’s group?
- Why do elements in the same group have similar physical and chemical properties?
- What do atomic radius and ionic radius mean to you?
- How do atomic radii vary in a period and in a group? How do you explain the variation?
- 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⁺
- 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.
- Explain why cations are smaller and anions larger in radius than their parent atoms?
- What is the significance of the terms ‘isolated gaseous atom’ and ‘ground state’ while defining the ionization enthalpy and electron gain enthalpy?
- Energy of an electron in the ground state of the hydrogen atom is –2.18×10⁻¹⁸ J. Calculate the ionization enthalpy of atomic hydrogen in terms of J mol⁻¹
- 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 a higher ΔiH than B
(ii) O has a lower ΔiH than N and F?
- 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?
- What are the various factors due to which the ionization enthalpy of the main group elements tends to decrease down a group?
- The first ionization enthalpy values (in kJ mol⁻¹) of group 13 elements are:
B – 801, Al – 577, Ga – 579, In – 558, Tl – 589
How would you explain this deviation from the general trend?
- Which of the following pairs of elements would have a more negative electron gain enthalpy?
(i) O or F (ii) F or Cl
- Would you expect the second electron gain enthalpy of O as positive, more negative or less negative than the first? Justify your answer.
- What is the basic difference between the terms electron gain enthalpy and electronegativity?
- How would you react to the statement that the electronegativity of N on the Pauling scale is 3.0 in all the nitrogen compounds?
- Describe the theory associated with the radius of an atom as it
(a) gains an electron (b) loses an electron
- Would you expect the first ionization enthalpies for two isotopes of the same element to be the same or different? Justify your answer.
- What are the major differences between metals and non-metals?
- 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 room temperature.
- The increasing order of reactivity among group 1 elements is Li < Na < K < Rb < Cs, whereas that among group 17 elements is F > Cl > Br > I. Explain.
- Write the general outer electronic configuration of s-, p-, d-, and f- block elements.
- Assign the position of the element having the outer electronic configuration
(i) ns²np⁴ for n = 3 (ii) (n–1)d²ns² for n = 4 (iii) (n–2)f⁷(n–1)d¹ns² for n = 6
- Predict the formulas 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 - 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 - 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 the value of the azimuthal quantum number (l) for the last subshell that received electrons in building up the electronic configuration. - 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 - 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 - 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 the removal of an electron from the core noble gas configuration.
(c) End of valence electrons is marked by a big jump in ionization enthalpy.
(d) Removal of an electron from orbitals bearing a lower n value is easier than from orbitals having a higher n value. - 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 - 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 - 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
Also Read: Theories of Learning in Psychology: Definition, Types, and Concepts Involved
Solutions
- The basic theme is to classify elements in such a way that elements with similar properties fall in the same group. This enables the prediction of properties and behavior of elements.
- Mendeleev used atomic mass to classify elements. However, to ensure properties were grouped properly, he sometimes altered the order based on atomic properties, not strictly by atomic mass.
- Mendeleev’s law was based on atomic mass, whereas Modern Periodic Law is based on atomic number, which gives a more consistent and accurate classification.
- The sixth period involves filling of 6s, 4f, 5d, and 6p orbitals. Total number of elements = 2 (6s) + 14 (4f) + 10 (5d) + 6 (6p) = 32 elements.
- Z = 114 lies in the 7th period and Group 14 (p-block).
- The third period and the Group 17 element is chlorine. Its atomic number is 17.
- (i) Element 103, Lawrencium (Lr), named after Lawrence Berkeley Laboratory. (ii) Element 106, Seaborgium (Sg), named after Seaborg’s group.
- Because elements in the same group have the same number of valence electrons, which determines chemical and physical properties.
- Atomic radius is the distance from the nucleus to the outermost shell of an atom. Ionic radius is the same, but for ions.
- Atomic radius decreases across a period due to increasing nuclear charge. It decreases a group due to the addition of shells.
- (i) Na⁺
(ii) Ca²⁺
(iii) Ne
(iv) Kr - (a) All are isoelectronic, having same number of electrons (10).
(b) Order of increasing radii: Al³⁺ < Mg²⁺ < Na⁺ < F⁻ < O²⁻ < N³⁻ - Cations are smaller because they lose electrons and have more nuclear pull. Anions are larger as they gain electrons and experience more repulsion.
- These terms ensure consistency in comparing energy changes. Energy values vary if the atom is not isolated or not in ground state.
- Ionization enthalpy = (2.18 × 10⁻¹⁸ J) × (6.022 × 10²³ mol⁻¹)
= 1.31 × 10⁶ J mol⁻¹ or 1312 kJ mol⁻¹ - (i) Be has a filled 2s orbital, making it more stable than B.
(ii) O has electron-electron repulsion in 2p⁴, reducing its ionization enthalpy. - Na has one electron in its outer shell, easily removed. But removing a second electron means taking it from a stable noble gas core. In Mg, both electrons are in outer shell.
- Ionization enthalpy decreases down the group due to increasing atomic size and shielding effect.
- Ga, In, and Tl show almost similar ionization enthalpies due to poor shielding effect of d and f orbitals, which does not effectively counter increasing nuclear charge.
- (i) F has more negative electron gain enthalpy than O.
(ii) Cl has more negative electron gain enthalpy than F due to lesser electron-electron repulsion. - It would be positive because the second electron is being added to a negatively charged ion, which repels the additional electron.
- Electron gain enthalpy is a measurable energy change. Electronegativity is a relative tendency to attract electrons in a bond.
- Electronegativity of nitrogen may vary depending on bonding environment, oxidation state, and hybridization, so the statement is not always true.
- (a) Radius increases due to added electron-electron repulsion.
(b) Radius decreases because of increased nuclear attraction on fewer electrons. - They would be almost the same. Ionization enthalpy depends on nuclear charge and electronic configuration, not mass
- Metals are electropositive, good conductors, malleable, and ductile.
Non-metals are electronegative, poor conductors, and brittle. - (a) Nitrogen (Z = 7)
(b) Calcium (Z = 20)
(c) Oxygen (Z = 8)
(d) Group 17 (contains Cl – gas, Br – liquid, I – solid) - Reactivity increases down Group 1 due to lower ionization energy. For Group 17, reactivity decreases due to less negative electron gain enthalpy.
- s-block: ns¹–²
p-block: ns²np¹⁻⁶
d-block: (n–1)d¹⁻¹⁰ns¹⁻²
f-block: (n–2)f¹⁻¹⁴(n–1)d⁰⁻¹ns² - (i) 3rd period, Group 16
(ii) 4th period, Group 4
(iii) 6th period, Group 3 (lanthanides) - (a) Element I (high ΔiH₂)
(b) Element II (low ΔiH₁)
(c) Element III (most negative ΔegH)
(d) Element V (positive ΔegH)
(e) Element IV
(f) Element VI - (a) Li₂O
(b) Mg₃N₂
(c) AlI₃
(d) SiO₂
(e) PF₅ or PF₃
(f) LuF₃ - c) principal quantum number
- (b) The d-block has 10 columns, not 8.
- (c) Nuclear mass
- (a) nuclear charge (Z)
- (d) Removal of electron from orbitals bearing lower n value is not easier than from higher n value.
- (d) K > Mg > Al > B
- (c) F > N > C > B > Si
- (b) F > O > Cl > N
NCERT Solutions Class 11 Chemistry (Part-1) Chapter 3: Classification of Elements and Periodicity in Properties
Download the Solutions of Other Chapters of Class 11 Chemistry
Related Reads
For more topics, follow LeverageEdu NCERT Study Material today!
