chemistry

CLASSIFICATION OF ELEMENTS AND PERIODICITY IN

 PROPERTIES OF ELEMENTS

TWO MARKS QUESTIONS

Q.1. Describe the two merits of long form periodic table over the Mendeleev’s periodic table?

Ans- 1. It removed the anomalies about the position of isotopes which existed in the Mendeleev’s table.

2. It relates the position of an element in the periodic table with its electronic configuration.

Q.2. What is a period in the periodic table? How do atomic sizes change in a period with an increase in atomic number?

Ans- The horizontal rows in periodic table are called as periods. The atomic sizes decrease in a period with an increase in atomic number.

Q.3. The outer electronic configuration of some elements are:

(a) 3s2 3p4    (b) 3d104s2    (c) 3s2 3p6 4s2

(d) 6s2 4f3

To which block of elements in the periodic table each of these belongs?

Ans- (a) p- Block  (b) d- Block (c) s- Block (d) f- Block

Q.4. What is meant by periodicity in properties of elements? What is the reason behind this?

Ans- The repetition of similar properties after regular intervals is called as periodicity. It is due to the similarity in the outer electronic configurations which gives rise to the periodic properties of the elements.

Q.5.  How do atomic radii vary in a group and a period?

Ans-   In group- Atomic size increases on moving from top to bottom.

In period- Atomic size decreases on moving left to right in a period.

Q.6. Arrange the following in the order of increasing radii:

(a) I, I⁺, I^-     (b) F, Cl, Br

Ans- (a) I⁺ < I < I⁺(b) O < N<  P

Q.7. Name the factors which affect the ionisation enthalpy of an element.

Ans-  (i) Size of atom or ion     (ii) Nuclear charge (iii) Electronic configuration

(iv) Screening effect         (v) Penetration effect of the electrons

Q.8. How does ionisation enthalpy vary in a group and a period? Ans- In Period- It increases from left to right

In group- It decreases down the group.

Q.9. Noble gases have zero electron gain enthalpy values. Explain.

Ans- Because the outer most shell of noble gases is completely filled and no more electrons can be added.

Q.10. Elements in the same group have equal valency. Comment on it.

Ans- Because the general outer most electronic configurations of the elements of a group remain same and they contain equal number of electrons in their respective outer most shells.