Chemistry

Classification of Elements and Periodicity in Properties

Question:

Discuss the main characteristics of four blocks of elements in the periodic table? Give their general electronic configuration.

Answer:

s-block elements:

  • They are highly reactive elements and thus occurs in combined state. On moving down the group their reactivity increases.
  • They have good reducing characters.
  • They generally form electropositive ion by losing 1 or 2 electrons, that’s why they are electro positive in nature.
  • They are good conductors of heat and electricity.

p-block elements:

  • Most of the p-block elements show variable oxidation states.
  • They include both metals and non-metals.
  • They are generally covalent in nature.
  • As move from left to right the non-metallic character of the element increases.
  • On moving down the group metallic character increases.

d-block elements:

  • d-block elements show variable oxidation states.
  •  They are generally paramagnetic in nature.
  • Their compounds are generally coloured. Those which form complex compounds.
  • Most of the elements and their compounds acts as catalyst.

f-block elements:

  • They are generally heavy metals having high melting and boiling points.
  • Their compounds are generally coloured.
  • Variable oxidation states are generally shown by these elements.
  • Most of Activities are radioactive.

General electronic configuration:
s-block —ns1-2
p-block —ns2 np1- 6
d-block —(n -1) d1 -10 ns0-2
f-block —(n – 2)f0-14 (n -1) d0- 1 ns2

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Classification of Elements and Periodicity in Properties

Q 1.

Give reasons:
(i) IE1  of sodium is lower than that of magnesium whereas  IE2  of sodium is higher than that of magnesium.
(ii) Noble gases have positive value of electron gain enthalpy.

Q 2.

Why are electron gain enthalpies of Be and Mg positive?

Q 3.

All transition elements are d-block elements, but all d-block elements are not transition elements. Explain.

Q 4.

Among alkali metals which element do you expect to be least electronegative and why?  

Q 5.

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

Q 6.

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 JMol-1.[Hint: Apply the idea of mole concept to derive the answer],

Q 7.

Discuss the main characteristics of four blocks of elements in the periodic table? Give their general electronic configuration.

Q 8.

Discuss and compare the trend in ionization enthalpy of the elements of group 1 with those of group 17 elements.

Q 9.

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

Q 10.

Explain why chlorine can be converted into chloride ion more easily as compared to fluoride ion from fluorine ?

Q 11.

What are representative elements?

Q 12.

Show by a chemical reaction with water that Na20 is a basic oxide and  Cl207  is an acidic oxide.

Q 13.

Name different blocks of elements in the periodic table. Give general electronic configuration of each block.

Q 14.

Which of the following elements can show covalency greater than 4?
(a) Be (b) P (c) S (d) B

Q 15.

Which of the following have no unit?
(a) Electronegativity (b) Electron gain enthalpy
(c) Ionisation enthalpy (d) Metallic character

Q 16.

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

Q 17.

Consider the following species:
N3-, O2-, F, Na+, Mg2+, Al3+
(a) What is common in them?
(b) Arrange them in order of increasing ionic radii?

Q 18.

Use periodic table to answer the following questions:
(a) Identify the element with five electrons in the outer subshell.
(b) Identify the element that would tend to lose two electrons.
(c) Identify the element that would tend to gain two electrons.

Q 19.


ncert-solutions-for-class-11-chemistry-chapter-3-classification-of-elements-and-periodicity-in-properties-2
ncert-solutions-for-class-11-chemistry-chapter-3-classification-of-elements-and-periodicity-in-properties-3
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 (d) the least reactive non-metal
(e) the metal which can form a stable binary halide of the formula MX2(X = halogen)
(f) the metal which can form a predominantly stable covalent halide of the formula MX (X = halogen)?

Q 20.

Which of the following statements related to the modem periodic table is incorrect?
(a) The p-block has six columns, because a maximum of 6 electrons can occupy all the orbitals in a p-subshell.
(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.

Q 21.

Why is ionization enthalpy of nitrogen greater than that of oxygen?

Q 22.

What is the cause of periodicity in properties of the elements? Explain with two examples.

Q 23.

Illustrate by taking examples of transition elements and non-transition elements that oxidation states of elements are largely based on electronic configuration.

Q 24.

Match the correct atomic radius with the element.

Column I (Element) Column II (Atomic radius (pm)
Be 74
C 88
0 111
B 77
N 66

Q 25.

Write down the outermost electronic configuration of alkali metals. How will you justify their placement in group 1 of the periodic table?

Q 26.

Write the drawbacks in Mendeleev's periodic table that led to its modification.

Q 27.

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

Q 28.

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

Q 29.

What is screening or shielding effect? How does it influence the ionization enthalpy ?

Q 30.

Arrange the following as stated: (i) N2, 02, F2, Cl2(Increasing order of bond dissociation energy) (ii) F, Cl, Br, I (Increasing order of electron gain enthalpy) (iii)  F2, N2, Cl2, O2(Increasing order of bond length).

Q 31.

The first ionisation enthalpy of magnesium is higher than that of sodium. On the other hand, the second ionisation enthalpy of sodium is very much higher than that of magnesium. Explain.

Q 32.

Consider the isoelectronic species, Na+, Mg2+, F and O2-. The correct order  of increasing length of their radii is

ncert-exemplar-problems-class-11-chemistry-chapter-3-classification-of-elements-and-periodicity-in-properties-1

Q 33.

In which of the following options order of arrangement does not agree with the variation of property indicated against it?
(a) Al3+ < Mg2+ < Na+ < F (increasing ionic size)
(b) B < C < N < O (increasing first ionization enthalpy)
(c) I < Br < Cl < F (increasing electron gain enthalpy)
(d) Li < Na < K < Rb (increasing metallic radius)

Q 34.

Among the elements B, Al, C and Si,
(a) which element has the highest first ionization enthalpy
(b) which element has the most metallic character?
Justify your answer in each case.

Q 35.

Arrange the elements N, P, O and S in the order of
(i) increasing first ionisation enthalpy.
(ii) increasing non-metallic character.
Give reason for the arrangement assigned.

Q 36.

Explain the deviation in ionization enthalpy of some elements from the general trend by using the given figure.
ncert-exemplar-problems-class-11-chemistry-chapter-3-classification-of-elements-and-periodicity-in-properties-10

Q 37.

Explain the following:
(a) Electronegativity of elements increases on moving from left to right in the periodic table.
(b) Ionisation enthalpy decreases in a group from top to bottom.

Q 38.

How does the metallic and non metallic character vary on moving from left to right in a period?

Q 39.

The radius of Na+ cation is less than that of Na atom. Give reason.

Q 40.

Discuss the factors affecting electron gain enthalpy and the trend in its variation in the periodic table.

Q 41.

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

Q 42.

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

Q 43.

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

Q 44.

Among the second period elements, the actual ionization enthalpies are in the order: Li Explain why
(i) Be has higher  âˆ†iH1than B ?
(ii) O has lower  âˆ†iH1 than N and F?

Q 45.

Considering the elements F, Cl, O and N, the correct order of their chemical reactivity in terms of oxidising property is:
(a) F > Cl> O > N (b) F > O > Cl> N (c) Cl> F > O > N (d) O > F > N > Cl

Q 46.

Give general electronic configuration off-block elements?

Q 47.

The electronic configuration of an element is Is 2s 2p 3s 3p 4s . Locate the element in the periodic table.

Q 48.

Elements A, B, C and D Iwoe atomic numbers 12,19, 29, and 36 respectively. On the basis of  electronic configuration, write to which group of the periodic table each element belongs.

Q 49.

Define the term ionization enthalpy? How does it vary along a period and along a group?

Q 50.

(a) How does atomic radius vary in group in the periodic table?
(b) Explain
(i) Radius of cation is less than that of the atom.
(ii) Radius of anion is more than that of the atom.
(iii) In iso-electronic ion, the ionic radii decreases with increase in atomic number.