Classification of Elements & Periodicity

What you'll learn

Learn how the modern periodic table is built from atomic number and electron arrangement, how to locate any element by its period, group and block, and how atomic radius, ionisation enthalpy and electronegativity change in predictable patterns.

This chapter has

Classification of Elements & Periodicity — solved practice questions

8 Class 11 Chemistry questions with step-by-step solutions. Attempt each, then reveal the answer.

1. Q1easy

   The modern periodic law states that the properties of elements are a periodic function of their:

   • Aatomic mass
   • Batomic number
   • Cnumber of neutrons
   • Datomic volume
   Show answer & solution

   Correct answer: (B) atomic number

   Following Moseley's work, the modern periodic law is based on atomic number, not atomic mass.

2. Q2easy

   The total number of periods in the modern (long form) periodic table is:

   • A18
   • B9
   • C8
   • D7
   Show answer & solution

   Correct answer: (D) 7

   The long form periodic table has 7 horizontal rows, called periods.

3. Q3easy

   The total number of groups in the modern periodic table is:

   • A7
   • B8
   • C18
   • D9
   Show answer & solution

   Correct answer: (C) 18

   The modern periodic table has 18 vertical columns, called groups.

4. Q4easy

   Elements belonging to the same group of the periodic table have the same number of:

   • Avalence electrons
   • Bprotons
   • Cneutrons
   • Doccupied shells
   Show answer & solution

   Correct answer: (A) valence electrons

   Elements in the same group have the same number of valence electrons, which gives them similar chemical properties.

5. Q5medium

   As we move from left to right across a period, the atomic radius generally:

   • Aincreases
   • Bdecreases
   • Cremains constant
   • Dfirst increases then decreases
   Show answer & solution

   Correct answer: (B) decreases

   Across a period the nuclear charge increases while electrons are added to the same shell, so effective nuclear charge increases and the atomic radius decreases.

6. Q6medium

   As we move down a group in the periodic table, the ionization enthalpy generally:

   • Aincreases
   • Bremains constant
   • Cdecreases
   • Dbecomes zero
   Show answer & solution

   Correct answer: (C) decreases

   Down a group the atomic size increases and shielding increases, so the outer electron is held less tightly and ionization enthalpy decreases.

7. Q7easy

   The element with the highest electronegativity on the Pauling scale is:

   • Afluorine
   • Boxygen
   • Cchlorine
   • Dnitrogen
   Show answer & solution

   Correct answer: (A) fluorine

   Fluorine is the most electronegative element, with a Pauling value of 4.0.

8. Q8medium

   The general outer electronic configuration of s-block elements is:

   • Ans2 np1-6
   • B(n-1)d1-10 ns0-2
   • Cns2 np6
   • Dns1-2
   Show answer & solution

   Correct answer: (D) ns1-2

   s-block elements (groups 1 and 2) have their last electron entering the ns orbital, giving the general configuration ns1-2.

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