AP 9th Class Physics 4th Lesson Questions and Answers Structure of the Atom

AP State Board new syllabus AP Board Solutions Class 9 Physics 4th Lesson Structure of the Atom Questions and Answers.

AP 9th Class Physical Science 4th Lesson Questions and Answers Structure of the Atom

9th Class Physics 4th Lesson Structure of the Atom Questions and Answers (Exercise)

Question 1.
Compare the properties of electrons, protons and neutrons.
Answer:

Property	Electron	Proton	Neutron
Location	It is located outside the nucleus.	It is located inside the nucleus.	It is located inside the nucleus.
Charge	It is negatively charged particle.	It is positively charged particle.	It has no charge.
Mass	It’s mass is about 1/2000 times that of a hydrogen atom.	It’s mass is taken as  one unit.	It’s mass is taken as one unit.
Attraction	It is attracted towards positively charged particle.	It is attracted towards negatively charged particle.	They do not get attracted to any charged particle.

Question 2.
What are the limitations of J. J.Thomson’s model of the atom ?
Answer:
Limitations of J.J. Thomson’s model of the atom are :

• It could not explain the results of experiments carried out by other scientists as there is no nucleus in the Thomson’s atomic model.
• Thomson atomic model fails to explain the stability of an atom as the positive charge and Thomson atomic model is spread all over and thus could not be justified.

Question 3.
What are the limitations of Rutherford’s model of the atom ?
Answer:
Limitations of Rutherford :

• Revolution of electron in circular orbit is not stable.
• Any particle in circular orbit would undergo acceleration.
• During acceleration particles radiate energy.
• Due to this they loose energy and fall into nucleus.
• Then the atom becomes unstable.
• Hence atom doesn’t exist.
• But atom is quite stable.
• He couldn’t able to explain why.

Question 4.
Describe Bohr’s model of the atom.
Answer:
Bohr’s model of the atom:

• Only certain special orbits known as discrete orbits of electrons are allowed inside the atom.
• While revolving in discrete orbits the electrons do not radiate energy.
• These orbits (or) shells are called energy levels.
• These shells are represented by letters K, L, M> N
• The energy of each orbital is represented by n = {1, 2, 3, 4 }

Question 5.
Compare all the proposed models of an atom given in this chapter.
Answer:
Comparison of atomic Models:

J.J. Thomson	Rutherford	Niels Bohr
Thomson explained electrical neutrality of atom.	Rutherford proposed that atom has a centre called nucleus.	Neils Bohr propose that electrons revolve around nucleus indiscrete orbits.

Question 6.
Summarise the rules for writing of distribution of electrons in various shells for the first eighteen elements.
Answer:
Rules for writing electron distribution based on Bohr – Bury postulates.

• The maximum number of electrons present in a shell is given by the formulae 2n².
• The maximum number of electron in different shells.

• The maximum number of electrons that can be accommodated in the outer orbit is 8.
• Electrons are not accommodated in a given shell unless the inner shells are filled.

Question 7.
Define valency by taking examples of silicon and oxygen.
Answer:
Valency : The combining capacity of an atom of an element is known as valency.

Question 8.
Explain with examples
(i) Atomic number
(ii) Mass number
(iii) Isotopes and
iv) Isobars.
Give any two uses of isotopes.
Answer:
i) Atomic number : The number of protons present in the nucleus of an atom is called proton number (Z).
Ex : Nitrogen -N has 7 protons
So, its atomic number Z = 7

ii) Mass number : Sum of the numbers of proton and neutron in the nucleus of the atom.
Ex: Nitrogen N has 7 protons and 7 neutrons.
A = Z+n
A = 7+7
A = 14 u (or) Da
Atomic Mass of N = 14

iii) Isotopes : Atoms of same element having same atomic number but different máss number.
Ex : Chlorine \({ }_{17}^{35} \mathrm{Cl} \) & \({ }_{17}^{37} \mathrm{Cl}\)

iv) Isobars: Atoms of different elements with different atomic number but same mass number.
Ex : Argon (Ar) Atomic number (Z) =18, Mass number (A)=40
Potassium (K) Atomic number (Z) =19, Mass number (A)=40

Question 9.
Na⁺ has completely filled K and L shells. Explain.
Answer:
Sodium (Na) = 11

To achieve stable configuration (octet) it has to loose 1 electron.
Na⁺

This makes Na⁺ has completely filled electrons.

Question 10.
If bromine atom is available in the form of, say, two isotopes \({ }_{35}^{79} \mathrm{Br}\) 49.7 % and ( 50.3% ), calculate the average atomic mass of bromine atom.
Answer:

Question 11.
The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes \({ }_8^{16} \mathrm{X}\) and \({ }_8^{18} \mathrm{X}\) in the sample ?
Answer:

Question 12.
If Z=3, what would be the valency of the element ? Also, name the element.
Answer:
Atomic Number = Proton Number

Valency =1
(Since the outermost shell has only one electron)
∴ The element with Z = 3 is Lithium.

Question 13.
Composition of the nuclei of two atomic species X and Y are given as under

Give the mass numbers of X and Y. What is the relation between the two species ?
Answer:

Mass Number (A) of X=Z+n=6+6 = 12 u (or) Da
Mass Number (A) of Y = Z+n = 6+8 = 14 u (or) Da

Relation between X and Y :

• The mass number of X and Y is 12 and 14 respectively.
• These two atomic species, X and Y have the same atomic number i.e., 6 but different mass numbers. So, they are isotopes of each other.

Question 14.
For the following statements, write T for True and F for False.

a) J.J. Thomson proposed that the nucleus of an atom contains only nucleons.
Answer: False

b) A neutron is formed by an electron and a proton combining together. Therefore, it is neutral.
Answer: False

c) The mass of an electron is about \(\frac{1}{2000}\) times that of proton.
Answer: True

d) An isotope of iodine is used for making tincture iodine, which is used as a medicine.
Answer: False

Put tick ( ✓ ) against correct choice and cross ( ✗ ) against the wrong choice in questions 15,16 and 17.

Question 15.
Rutherford’s alpha-particle scattering experiment was responsible for the discovery of
a) Atomic Nucleus
b) Electron
c) Proton
d) Neutron
Answer:
a) Atomic Nucleus

Question 16.
Isotopes of an element have
a) the same physical properties
b) different chemical properties
c) different number of neutrons
d) different atomic numbers.
Answer:
c) different number of neutrons

Question 17.
Number of valence electrons in Cl^– ion are :
a) 16
b) 8
c) 17
d) 18
Answer:
b) 8

Question 18.
Which one of the following is a correct electronic configuration of sodium ?
a) 2,8
b) 8,2,1
c) 2,1,8
d) 2,8,1
Answer:
d) 2,8,1

Question 19.
Complete the following table.

Atomic Number	Mass Number	Number of Neutrons	Number of Protons	Number of Electrons	Name of the Atomic  Species
9	–	10	–	–	–
16	32	–	–	–	Sulphur
–	24	–	12	–	–
–	2	–	1	–	–
–	1	0	1	0	–

Answer:

Atomic Number	Mass Number	Number of Neutrons	Number Protons	Number of Electrons	Name of the Atomic Species
9	19	10	9	9	Flourine
16	32	16	16	16	Sulphur
12	24	12	12	12	Magnesium
1	2	1	1	1	Deuterium
1	1	0	1	0	Protium

9th Class PS 4th Lesson Questions and Answers (InText)

Question 1.
What are canal rays ?
Answer:

• Canal rays are a type of positively charged ion beam that was discovered by Eugen Goldstein in 1886.
• These rays are created when a high voltage is applied to a gas in a discharge tube.
• The canal rays are so named because they form a beam that travels in a narrow channel or “canal” through the gas.

Question 2.
If an atom contains one electron and one proton, will it carry any charge or not ?
Answer:
In this case, since the electron has a negative charge and the proton has a positive charge, the atom will have a net charge of -1+1=0, which means it is neutral.

Question 3.
On the basis of Thomson’s model of an atom, explain how the atom is neutral as a whole.
Answer:
Thomson Proposed that,

• An atom consists of a positively charged sphere and the electrons are embedded in it.
• The negative and positive charges are equal in magnitude. So, the atom as whole is electrically neutral.

So, he compared this to pudding model in which electrons and protons distributed evenly, so atom as whole it is neutral.

Question 4.
On the basis of Rutherford’s model of an atom, which subatomic particle is present in the nucleus of an atom?
Answer:
Positively charged proton is present in the nucleus.

Question 5.
Draw a sketch of Bohr’s model of an atom with three shells.
Answer:
Sketch of Bohr’s model of an atom :

Question 6.
What do you think would be the observation if the α – particle scattering experiment is carried out using a foil of a metal other than gold ?
Answer:

• A gold foil can be made very thin.
• A thin gold foil will have concentration of just 1000 atoms.
• Other metals can’t be made that much thin.
• So, the result wouldn’t be same.

Question 7.
Name the three sub-atomic particles of an atom.
Answer:
Three sub-atomic particles of an atom :

• Electrons
• Protons
• Neutrons

Question 8.
Helium atom has an atomic mass of 4u and two protons in its nucleus. How many neutrons does it have?
Answer:
Helium (He) atom has
Number of protons p = 2;
Atomic Mass A = 4 u (or) Da
Atomic Mass = No. of Protons + No. of Neutrons
A = Z+n  [∵ Atomic number = Proton Number ⇒Z = p]
4 = 2+n
n = 4-2=2
Helium (He) atom has 2 neutrons.

Question 9.
Write the distribution of electrons in carbon and sodium atoms.
Answer:
Carbon : 6
Distribution of electrons :
2 electrons in the first shell
2 electrons in the second shell
2 electrons in the third shell

Sodium : II
Distribution of electrons:
2 electrons in the first shell
2 electrons in the second shell
6 electrons in the third shell
1 electron in the fourth shell

Question 10.
If K and L shells of an atom are full, then what would be the total number of electrons in the atom?
Answer:
Number of electrons in K – shell =2
Number of electrons in L- shell =8
Total number of electrons =2+8=10 electrons.

Question 11.
How will you find the valency of chlorine, sulphur and magnesium?
Answer:
Valency :
a)

Valency = Octet – No. of electrons in outer shell
Valency of Chlorine =8-7=1

Question 12.
If number of electrons in an atom is 8 and number of protons is also 8, then (i) what is the atomic number of the atom ? and (ii) what is the charge on the atom?
Answer:
i) Atomic number = Proton number =8
ii) Atom doesn’t carry any charge.
No. of electrons = No. of Protons

Question 13.
With the help of Table 4.1, find out the mass number of oxygen and sulphur atom.
Answer:
Mass Number :
a) Oxygen: A = Z+n=8+8
Mass number of O=16g

b) Sulphur :
A = Z + n
= 16+16=32 g
Mass number of S = 32g

Question 14.
For the symbol H, D and T tabulate three sub-atomic particles found in each of them.
Answer:

Element	P	1	n
Hydrogen	1	1	0
Deuterium	1	1	1
Tritium	1	1	2

Question 15.
Write the electronic configuration of any one pair of isotopes and isobars.
Answer:
Electronic Configuration of Isotopes:

Electronic Configuration of Isobars:

9th Class Physical Science Chapter 4 Questions and Answers (Lab Activities)

(Page No. 76) Activity – 4.1

Question 1.
Write an activity for understanding the nature of charged particles.
Procedure :
A) Comb dry hair. Does the comb, then attract small pieces of paper?
Answer:
Yes, comb gets electrically charged and it attracts pieces of paper.

B) Rub a glass rod with a silk cloth and bring the rod near an inflated balloon. Observe what happens?
Answer:

• When a glass rod is rubbed with silk, electrons are transferred from the glass rod to the silk. Since the glass rod loses electrons, it becomes rich in positive charge. Similarly, the silk cloth becomes negatively charged. Glass rod attracts the balloon.
• From these activities, we conclude that on rubbing two objects together, they become electrically charged.

(Page No. 84) Activity – 4.2

Question 2.
How do you prepare a model of electronic configuration of the first eighteen elements?
Answer:

• Make a static atomic model displaying electronic configuration of the first eighteen elements.
• The composition of atoms of the first eighteen elements is given Table.

Table: Composition of Atoms of the First Eighteen Elements with Electron Distribution in Various Shells.

Answer:

Students have to prepare a static model of the electronic configuration of 18 elements by using cardboard and other material (except thermocol).