9TH Class Chemistry Chapter - 3 Periodic Table and Periodicity of Properties ( SOLVED EXERCISE )

Chapter - 3

Periodic Table and Periodicity of Properties

EXERCISE

 

Multiple Choice Questions

Put a (✓) on the correct answer

            1. The atomic radii of the elements in Periodic Table:

(a)    Increase from left to right in a period

(b)   Increase from top to bottom in a group    ✓

(c)    Do not change from left to right in a period

(d)   Decrease from top to bottom in a group

2. The amount of energy given out when an electron is added to an atom is called:

(a)    Lattice energy

(b)   Ionization energy

(c)    Electronegativity

(d)   Electron affinity    ✓

3. Mendeleev Periodic Table was based upon the:

(a)    Electronic configuration

(b)   Atomic mass    ✓

(c)    Atomic number

(d)   Completion of a subshell

4. Long form of Periodic Table is constructed on the basis of:

(a)    Mendeleev Postulate

(b)   Atomic number    ✓

(c)    Atomic mass

(d)   Mass number

5. 4^th and 5^th period of the long form of Periodic Table are called:

(a)    Short periods

(b)   Normal periods

(c)    Long periods    ✓

(d)   Very long periods

6. Which one of the following halogen has lowest electronegativity?

(a)    Fluorine

(b)   Chlorine

(c)    Bromine

(d)   Iodine    ✓

7. Along the period, which one of the following decreases:

(a)   Atomic radius    ✓

(b)   Ionization energy

(c)    Electron affinity

(d)   Electronegativity

8. Transition elements are:

(a)    All gases

(b)   All metals    ✓

(c)    All non-metals

(d)   All metalloids

9. Mark the incorrect statement about ionization energy:

(a)    It is measured in kJmol^-

(b)   It involves release of energy

(c)    It decreases in a period    ✓

(d)   It decreases in a group

10. Point out the incorrect statement about electron affinity:

(a)    It is measured in kJmol^-

(b)   It involves release of energy

(c)    It decreases in a period    ✓

(a)    It decreases in a group

Short answer questions.

1. Why are noble gases not reactive?

Ans.

    The noble gases are not reactive because they have completely filled valence shells with 2 or 8 electrons and do not react with other elements to form compounds.

2. Why Cesium (at. no.55) requires little energy to release its one electron present in the outermost shell?

Ans.

    Cesium requires little energy to release its outer most electrons due to following reasons:

    (i)                 It has bigger atomic size.

    (ii)               High shielding effect

    (iii)             Low ionization energy

    (iv)             Weak nuclear hold / attraction on valence electrons.

3. How is periodicity of properties dependent upon number of protons in an atom?

Ans.

    If atoms are arranged in order of increasing atomic number, their properties are repeated after regular intervals. This is called periodicity of properties. It depends upon atomic number.

4. Why shielding effect of electrons make cation formation easy?

Ans.

    The electrons present between the nucleus and the outer most shell of an atom, reduce the nuclear charge felt by the electrons present in the outer most shell. Thus shielding effect of electrons makes cation formation easy.

5. What is the difference between Mendeleev’s periodic law and modern periodic law?

Ans.

Mendeleev’s Periodic Law	Modern Periodic Law
Properties of elements are periodic function of their atomic masses.	Properties of elements are periodic function of their atomic numbers.

6. What do you mean by groups and periods in the Periodic Table?

Ans.

        Periods:

        The horizontal rows of elements in a periodic table are called periods. There are 7 periods in the periodic table.

        Groups:

        The vertical columns in a periodic able are called groups. There are 18 groups in the periodic table. These groups are numbered from left to right as 1 to 18.

7. Why and how elements are arranged in 4^th period?

Ans.

    

    The elements of 4^th period are arranged by increasing order of their atomic number. It consists of 18 elements.

8. Why the size of atom does not decrease regularly in a period?

Ans.

    When we move from left to right in a period, the size of atom decreases gradually but not regularly because of increase in shielding effect.

9. Give the trend of ionization energy in a period.

Ans.

    The value of ionization energy increases from left to right along the period.

    Reasons:

    (i)                 The size of atoms reduces.

    (ii)               Valence electrons are held strongly by the electrostatic force of nucleus.