Chemistry

Classification of Elements and Periodicity in Properties

Question:

State the Modem Periodic Law.

Answer:

Modem Periodic Law states that physical and chemical properties of the elements are a periodic function of their atomic numbers.

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Classification of Elements and Periodicity in Properties

Q 1.

Define electron gain enthalpy. What are its units?

Q 2.

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

Q 3.

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?

Q 4.

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

Q 5.

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

Q 6.

Ionisation enthalpies of elements of second period are given below:
Ionisation enthalpy/kJ mol-1: 520, 899, 801, 1086, 1402, 1314, 1681, 2080. Match the correct enthalpy with the elements and complete the graph given in figure. Also write symbols of elements with their atomic number.
ncert-exemplar-problems-class-11-chemistry-chapter-3-classification-of-elements-and-periodicity-in-properties-5

Q 7.

Discuss briefly the various factors on which ionization enthalpy depends.

Q 8.

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 9.

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 10.

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

Q 11.

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

Q 12.

What are major differences between metals and non-metals?

Q 13.

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

Q 14.

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 15.

What are representative elements?

Q 16.

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

Q 17.

Discuss the main features of long form of the periodic table. What are the advantages of long . form of periodic table?

Q 18.

Choose the correct order of atomic radii of fluorine and neon (in pm) out of the options given below and justify your answer.
(i) 72,160 (b) 160,160 (c) 72,72 (d) 160,72

Q 19.

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

Q 20.

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

Q 21.

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 22.

Write the general electronic configuration of spd, and f-block elements?

Q 23.

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

Q 24.

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

Q 25.

The first ionization enthalpies of Na, Mg, A1 and Si are in the order
(a)       Na < Mg > A1 < Si                                                    
(b)         Na>Mg>Al>Si
(c)       Na < Mg < A1 < Si                                                    
(d)       Na > Mg > A1 < Si

Q 26.

What do you understand by exothermic reaction and endothermic reaction? Give one example of each type.

Q 27.

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

Q 28.

Electronic configurations of some elements are given in column I and their electron gain enthalpies are given in column II. Match the electronic configuration with electron gain enthalpy.

Column I

(Electronic configuration)

Column II '

(Electron gain enthalpy/kJ moL-1

(i) 1s2 2s2 2p6 A. -53
(ii) ls22s22p63sl B. -328
(iii) ls22s22p5 C. -141
(iv) 1s2 2S2 2p4 D. +48

Q 29.

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

Q 30.

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

Q 31.

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

Q 32.

Which two elements of the following belong to the same period?
Al, Si, Ba and O

Q 33.

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

Q 34.

What are inner transition metals? Why are they called rare earth metals?

Q 35.

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 36.

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 37.

The electronic configuration of gadolinium (Atomic number 64) is

ncert-exemplar-problems-class-11-chemistry-chapter-3-classification-of-elements-and-periodicity-in-properties-2

Q 38.

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 39.

Electronic configurations of four elements A, B, C and D are given below:
(A) 1s2 2s12p6                          
(B)  1 s2 2s2 2p4
(C)     1s2 2s2 2p6 3s1                                                                    
(D)       Is2 2s2 2p5

Which of the following is the correct order of increasing tendency to gain electron?

(a) A < C < B < D
(b)         A < B < C < D
(c)       D < B < C < A                                                                  
(d)         D < A< B < C

Q 40.

Which of the following sequences contain atomic numbers of only representative elements?
(a) 3, 33, 53, 87
(b) 2, 10, 22, 36
(c) 7, 17,25,37,48
(d) 9,35,51,88

Q 41.

Which of the following statements are correct?
(a) Helium has the highest first ionization enthalpy in the periodic table.
(b) Chlorine has less negative electron gain enthalpy than fluorine.
(c) Mercury and bromine are liquids at room temperature.
(d) In any period, atomic radius of alkali metal is the highest.

Q 42.

Which of the following sets contain only isoelectronic ions?
(a) Zn2+, Ca2+, Ga3+, Al3+                                              
(b) K+, Ca2+, Sc3+, Cl
(c) P3-, S2- Cl,K+                                                    
(d) Ti4+, Ar, Cl3+, V5+

Q 43.

An element belongs to 3rd period and group-13 of the periodic table. Which of the following properties will be shown by the element?
(a) Good conductor of electricity
(b) Liquid, metallic
(c) Solid, metallic    
(d) Solid, non metallic

Q 44.

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 45.

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 46.

In what manner is the long form of periodic table better than Mendeleev's
periodic table? Explain with examples.

Q 47.

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

Q 48.

What is the basic difference in approach between Mendeleev’s Periodic Law and the Modem Periodic Law?

Q 49.

In terms of period and group where will you locate the element with z = 114?

Q 50.

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