ONE MARKS =>CHAPTER-3 CLASSIFICATION OF ELEMENTS AND PERIODICITY

ONE MARK QUESTIONS

Q1. Select the species which are iso-electronic (same number of electron) with
each other.
(1) Ne
(2) Cl^-(3) Ca²⁺
(4) Rb⁺
Ans-The Cl^- and Ca²⁺. Both have 18 e^- each.


Q.2. What the elements of a group have common among them?
Ans- They have same number of electrons in the valence shell.

Q.3. What the s- and p- block elements are collectively called?
Ans- Representative elements.


Q.4. Define atomic radius.
Ans- The one-half the distance between the nuclei of two covalently bonded atoms of the same element in a molecule is called as atomic radius.


Q.5. State the modern periodic law.
Ans- The physical and chemical properties of the elements are the periodic function of their atomic numbers.







Q.6. Name the groups of elements classified as s-, p- and d- blocks.
Ans- s- block= 1,2 (including He),             p- block= 13 to 18 (except He),       d- block= 3 to 12.


Q.7. Define the term ionisation enthalpy.
Ans- The energy required to remove the outer most electron from the valence shell of an isolated gaseous atom is called as ionisation enthalpy.


Q.8.In how many groups and periods the elements in modern periodic table are classified?
Ans- In 18 groups and 7 periods.


Q.9. What do you mean by electronic configuration of the elements?
Ans- The systematic distribution of the electrons among the orbitals of an atom of an element according to increasing order of their energies is called as electronic configuration of that element.