Chapter 3: Classification of Elements and Periodicity in Properties

Q1Written answer

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

(i) F- < O2– < Mg2+ < Na+

(ii) Mg2+ < Na+ < F– < O2–

(iii) O2– < F– < Na+ < Mg2+

(iv) O2– < F– < Mg2+ < Na+

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Ans: (ii)

All the given ions are isoelectronic species thus their radii depend upon the charge more the negative charge higher would be the atomic radii and higher the positive charge lesser would be the atomic radii.

Q2Written answer

Which of the following is not an actinoid?

(i) Curium (Z = 96)

(ii) Californium (Z = 98)

(iii) Uranium (Z = 92)

(iv) Terbium (Z = 65)

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Ans: (iv)

Actinoids possess Z=90-103.

Terbium is lanthanoid.

Q3Written answer

The order of screening effect of electrons of s, p, d and f orbitals of a given shell of an atom on its outer shell electrons is:

(i) s > p > d > f

(ii) f > d > p > s

(iii) p < d < s > f

(iv) f > p > s > d

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Ans: (i)

The orbitals nearer to the nucleus possess more shielding effect.

Q4Written answer

The first ionisation enthalpies of Na, Mg, Al and Si are in the order:

(i) Na <Mg>Al<Si

(ii) Na>Mg>Al>Si

(iii) Na<Mg <Al<Si

(iv) Na>Mg>Al<Si

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Ans: (i)

As Mg contains fully filled 3s orbital thus its ionisation is higher than that of Na and Al.

Q5Written answer

The electronic configuration of gadolinium (Atomic number 64) is

(i) (Xe) 4f35d56s2

(ii) (Xe) 4f75d26s1

(iii) (Xe) 4f75d16s2

(iv) (Xe) 4f85d66s2

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Ans: (iii)

Gadolinium is a lanthanoid which belongs to the f-block elements with electronic configuration (n-2)f14(n-1)d0-1ns2

Q6Written answer

The statement that is not correct for periodic classification of elements is:

(i) The properties of elements are periodic function of their atomic numbers. (ii) Non metallic elements are less in number than metallic elements.

(iii) For transition elements, the 3d-orbitals are filled with electrons after 3p-orbitals and before 4s-orbitals.

(iv) The first ionisation enthalpies of elements generally increase with increase in atomic number as we go along a period.

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Ans: (iii)

As per Aufbau principle 3d orbitals are filled first than 4s as due to lower n value.

Q7Written answer

Among halogens, the correct order of amount of energy released in electron gain (electron gain enthalpy) is:

(i) F > Cl > Br > I

(ii) F < Cl < Br < I

(iii) F < Cl > Br > I

(iv) F < Cl < Br < I

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Ans: (i)

The electron gain enthalpy decreases down the group, however as the size of F atom is much smaller thus it leads to repulsion upon addition of electrons on its 2p orbital for this electron gain enthalpy of Cl is higher than that of F.

Q8Written answer

The period number in the long form of the periodic table is equal to

(i) magnetic quantum number of any element of the period.

(ii) atomic number of any element of the period.

(iii) maximum Principal quantum number of any element of the period.

(iv) maximum Azimuthal quantum number of any element of the period.

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Ans: (iii)

Period number indicates the maximum value of principal quantum number.

Q9Written answer

The elements in which electrons are progressively filled in 4f-orbital are called

(i) actinoids

(ii) transition elements

(iii) lanthanoids

(iv) halogens

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Ans: (iii)

The lanthanides which belong to the f-block elements are the elements where 4f-orbitals are filled progressively.

Q10Written answer

Which of the following is the correct order of size of the given species:

(i) I > I – > I +

(ii) I + > I – > I

(iii) I > I + > I –

(iv) I – > I > I +

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Ans: (iv)

I+ possess the highest effective nuclear charge whereas I- possess the least among the given species.

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Multiple Choice Questions (Type-I)