Chemistry

Classification of Elements and Periodicity in Properties

Question:

Discuss the factors that influence the magnitude of ionization enthalpy. What are the general trends of variation of ionization enthalpy in the periodic table? Explain.

Answer:

Factors affecting Ionization enthalpy.

  1. Atomic size. With the increase in atomic size, the number of electron shells increases and thus the force of attraction between the electrons and the nucleus decreases. Therefore the ionization enthalpy decreases.
  2. Nuclear charge. As the nuclear charge increases the attraction for the electron also increases that’s why ionization enthalpy increases.
  3. Screening or shielding effect. In a multi-electron atom, the electron present in the inner shells shield the electrons in the valence shell as a result these electrons
    experience less attraction from the nucleus. This leads to lesser ionization enthalpy.
    • Variation along a period. On moving from left to right in a period the nuclear charge increases and the atomic size decreases as a result ionization enthalpies are expected to increase.
    • Variation within a group. On moving down the group as the atomic size of the elements increases that’s why ionization enthalpy decreases down the group.
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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.

(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.

Q 5.

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

Q 6.

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

Q 7.

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 8.

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

Q 9.

Those elements impart colour to the flame on heating in it, the atoms of which require low energy for the ionization (i.e., absorb energy in the visible region of spectrum). The elements of which of the following groups will impart colour to the flame?
(a) 2 (b) 13 (c) 1 (d) 17

Q 10.

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 11.

What do you understand by ‘Representative elements’? Name the groups whose elements are called representative elements.

Q 12.

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

Q 13.

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 14.

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

Q 15.

What are Dobereiner’s triads? Name two such triads.

Q 16.

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

Q 17.

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

Q 18.

Justify the given statement with suitable examples "the properties of the elements are a periodic function of their atomic numbers".

Q 19.

Which has a larger radius?
(i)Mg or Ca (ii) S or Cl

Q 20.

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

Q 21.

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 22.

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

Q 23.

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 24.

Which of the following pairs of elements would have a move negative electron gain enthalpy?  (i) O or F (ii) F or Cl.

Q 25.

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

Q 26.


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 27.

In the modem periodic table, the period indicates the value of
(a)atomic number (b) mass number (c) principal quantum number (d) azimuthal quantum number?

Q 28.

What are horizontal rows and vertical columns of the periodic table called?

Q 29.

Define electron gain enthalpy. What are its units? Discuss the factors which influence the electron gain enthalpy.

Q 30.

The formation of the oxide ion, 02-(g), from oxygen atom requires first an exothermic and then an endothermic step as shown below:
O(g) + e→0 (g), ∆H= -141 kJ mol-1
0(g) + e→O2 (g), ∆H = +780 kJ mol-1
Thus process of formation of O2- ion in gas phase is unfavourable even though O2- is isoelectronic with neon. It is due to the fact that

(a) Oxygen is more electronegative.
(b) Addition of electron in oxygen results in larger size of the ion.
(c) Electron repulsion outweighs the stability gained by achieving noble gas configuration.
(d) 0 ion has comparatively smaller size than oxygen atom.

Q 31.

Identify the group and valency of the element having atomic number 119. Also predict the outermost electronic configuration and write the general formula of its oxide.

Q 32.

First member of each group of representative elements (i.e., s and p-block elements) shows anomalous behaviour. Illustrate with two examples.

Q 33.

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 34.

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

Q 35.

The first ionization enthalpy values (in kJ mol -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?

Q 36.

Give the electronic configuration of the transition elements. Write their four important characteristics.

Q 37.

Define electron gain enthalpy. What are its units?

Q 38.

Discuss the factors that influence the magnitude of ionization enthalpy. What are the general trends of variation of ionization enthalpy in the periodic table? Explain.

Q 39.

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 40.

p-Block elements form acidic, basic and amphoteric oxides. Explain each property by giving two examples and also write the reactions of these oxides with water.

Q 41.

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

Q 42.

Which element do you think would have been named by
(i)Lawrence Berkeley Laboratory
(ii)Seaborg’s group?

Q 43.

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

Q 44.

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

Q 45.

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

Q 46.

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

Q 47.

What are major differences between metals and non-metals?

Q 48.

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) Phosphorous pentafluoride (f) Element 71 and fluorine.

Q 49.

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

Q 50.

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