NCERT Solutions for Class 9 Science Chapter 4 contains all the main and important topics which have a complete and detailed description. NCERT Solutions for Class 9 Science Chapter 4 will help the students of class 9 to understand concepts.
NCERT Solutions for Class 9 Science Chapter 4
NCERT Solutions for Class 9 Science Chapter 4 covers the complete syllabus. Chapter
4 science class 9 ncert solutions are based on NCERT science books of
science for class 9.
The
students can download ncert class 9 science chapter 4 solutions in PDF format
for offline use.
Table of Contents
1. Chapter 4 Class 9 Science NCERT Solutions Overview
2. Science Chapter 4 Class 9Questions-Answers
3. Class 9 ScienceChapter 4 Exercise Question- Answers
4. Important Points of NCERTSolutions Class 9 Science Chapter 4
5. Facts About NCERT Class 9Science Chapter 4 Solutions
6. Important Oral Questions-Answersof Ch 4 Class 9 Science
NCERT Solutions Class 9 Science Chapter 4
You must
know the complete overview of ncert solutions class 9 science chapter 4 before you go through science chapter 4 class
9 ncert solutions.
Chapter 4 Class 9 Science NCERT Solutions Overview
1. Charged
Particles in Matter
i. Discovery
of electron
ii.Determination
of charge to mass ratio(e/m) of electrons
iii. Charge
on the electron
iv.
Mass of the electron
v.
Discovery of proton- Experiment of anode rays or canal rays
2. The
Structure of an Atom
i.Thomson’s
atomic model – Features and drawbacks
ii. Rutherford’s
atomic model
a.Alfa
particle scattering experiment
b.Drawbacks
of Rutherford’s atomic model
iii.
Bohr’s Atomic model
iv.
Discovery of neutron
v.
Atomic Number and Mass Number
3. How
are Electrons Distributed in Different Orbits (shells)?
i.
Electronic configuration
ii.
Concept of Valency
iii.
More facts about valency
iv.isotopes-
Characteristics
v.
Applications of Isotopes
vi.
Isobars
vi.
Fractional atomic mass
Students of CBSE affiliated schools, RBSE, and all other states can download class 9 science chapter 4 solutions in English medium in PDF format for free.
Science Chapter 4 Class 9 Question- Answers
Chapter- 4 Structure of the Atom
Science chapter 4 class 9 questions- answers From page No. 47
Q1. What are
canal rays?
Ans. These rays are positively charged radiations
which are called canal rays.
Q2. If an atom
contains one electron and one proton. Will it carry any charge or not?
Ans. The atom containing one electron and
one proton will not carry any charge and it is neutral because one positive
charge (Proton) balances one negative charge (electron)
Science chapter 4 class 9 questions- answers from Page No. 49
Q1. On the basis of Thomson’s
model of an atom. Explain how the atom is neutral as a whole.
Ans. According to Thomson’s atomic model – An atom consists of a positively charged sphere and electrons are embedded in it. The positive charges and negative charges are equal in magnitude so an atom is neutral.
Q2. On the basis of Rutherford’s
model of an atom, which subatomic particle is present in the nucleus of an
atom?
Ans.
Protons
Q3. Draw a sketch of Bohr's model
of an atom with three shells.
Ans.
 |
| Bohr's model of an atom |
Q4. What do
you think would be the observation if the
Ans. If the
Science chapter 4 class 9 questions- answers from Page No. 49
Q.1 Name the three sub-atomic particles of an atom.
Ans. Electrons,
protons and neutrons.
Q.2 Helium atom has an atomic mass of 4 μ and two protons in
its nucleus. How many neutrons does it have?
Ans.
Atomic mass = Number of protons + Number of neutrons
4 = 2 + Number of
neutrons
Number of
neutrons = 4 - 2 = 2
See Also
Science chapter 4 class 9 questions- answers from Page No. 50
Q.1 Write the distribution of electrons in carbon and sodium
atoms.
Ans.
|
For Carbon
|
|
Atomic
number = 6
|
|
Number
of protons =6
|
|
Number
of protons = Number of electrons
|
|
Electronic
distribution = K L
2 4
|
|
For Sodium
|
|
Atomic
number = 11
|
|
Number
of protons =6
|
|
Number
of protons = Number of electrons
|
|
Electronic distribution = K L
M 2 8 1
|
|
Ans. K
shell can hold 2 electrons
While L shell can hold 8 electrons
When both the shells are full, there will be (8+2) = 10) electrons in the atom.
Science chapter 4 class 9 questions- answers from Page No. 52
Q1. How will you find the valency of chlorine, sulfur and magnesium?
Ans.
|
Valency – The combining capacity of an atom is
known as valency. |
|
For chlorine |
|
Atomic number =17 |
|
Protons = 17 |
|
Electrons =17 |
|
Electron distribution = K L M 2 8 7 |
|
Chlorine needs 1 electron to complete its outermost
shell |
|
So its valency is -1 (accepts one electron) |
Valency – The combining capacity of an atom is known as valency.
For Sulphur |
Atomic number =16 |
Protons = 16 |
Electrons =16 |
Electron distribution = K L M 2 8 6 |
Sulfur needs 2 electrons to complete its outermost shell |
So its valency is -2 (accepts two-electron) |
For Magnesium |
Atomic number =12 |
Protons = 12 |
Electrons =12 |
Electron distribution = K L M 2 8 2 |
Magnesium will donate 2 electrons to complete its outermost shell |
So its valency is +2 (donates one electron) |
Science chapter 4 class 9 questions- answers from Page No. 52
Q.1If the number of electrons in an atom is 8 and the 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?
Ans.
|
(i)
Atomic number = Number of Protons =8 |
|
(ii)
Number of electrons = number of protons, so the atom will be neutral. There is no charge on the atom |
Q.2 With the help of the table given, find out the mass number of oxygen and sulfur atom.
Table: Composition of Atoms of the First Eighteen Elements with Electron Distribution in various Shells
|
Name
of Element |
Symbol |
Atomic Number |
Number of Protons |
Number of Neutrons |
Number of Electrons |
Distribution of Electrons |
Valency |
|||
|
K |
L |
M |
N |
|||||||
|
Hydrogen
Helium
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon Sodium Magnesium Aluminium
Silicon
Phosphorus Sulphur
Chlorine
Argon
|
H He Li Be B C N O F Ne Na Mg A1 Si P S
CI Ar |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 |
- 2 4 5 6 6 7 8 10 10 12 12 14 14 16 16 18 22 |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 |
1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 |
- - - 1 2 3 4 5 6 7 8 8 8 8 8 8 8 8 |
- - - - - - - - - - 1 2 3 4 5 6 7 8 |
- - - - - - - - - - - - - - - - - - |
1 0 1 2 3 4 3 2 1 0 1 2 3 4 3.5 2 1 0 |
Ans.
|
For Oxygen |
|
Number
of protons = 8 |
|
Number
of neutrons =8 |
|
Atomic
number= 8 |
|
Mass
Number = P +N = 8 + 8 =16 |
|
For Sulphur
|
|
Number
of protons = 16 |
|
Number
of neutrons =16 |
|
Atomic
number= 16 |
|
Mass
Number = P +N = 16 + 16 =32 |
Science chapter 4 class 9 questions- answers from Page No. 53
Q.1For the symbols H, D and T tabulate three sub-atomic
particles found in each of them.
Ans.
|
For H.
|
|||||||||||
|
Atomic
number = 1
|
|||||||||||
|
Mass number = 1 |
|||||||||||
|
Number of electrons = 1 |
|||||||||||
|
Number of neutrons = 1-1 = 0 |
|||||||||||
|
Q.2 Write the electronic configuration of any one pair of isotopes and isobar.
Ans. Isotopes – Isotopes are atoms having the same atomic number but different mass numbers.
Isotopes 6C12 6C14 |
Electronic Configuration K L K L |
2 4 2 4 |
Isobars – Isobars are atoms having the same mass number but different atomic numbers.
Isotopes 20Ca40 18Ca40 |
Electronic Configuration K L M N K L M |
2 8 8 2 2 8 8 |
|
|
Class 9 Science Chapter 4 Exercise Question -Answers
Q.1Compare the properties of electrons, protons, and neutrons.
Ans. Comparison between properties of Electron, Proton, and Neutron
Properties | Electron | Proton | Neutron |
Mass
Relative mass
Relative charge Location in the atom | 9.109 × 10-28 g
-1 Outside Nucleus | 1.673 × 10-24 g
+1
Nucleus | 1.676 × 10-24 g
0
Nucleus |
Q.2 What are the limitations of J.J. Thomson’s model of the atom?
Ans. According to the J.J. Thomson model of an atom, electrons are embedded all over in the positively charged sphere. But experiments show that protons are present only in the nucleus and electrons revolve around the nucleus
Q.3 What are the limitations of Rutherford’s model of the atom?
Ans. According to Rutherford’s model of an atom, electrons revolve in a circular orbit around the nucleus. But such a particle would undergo acceleration and radiate energy and ultimately would lose its energy and fall into the nucleus. Now the atoms would become unstable, but atoms are quite stable.
This was not explained through Rutherford’s model of the atom.
Q.4 Describe Bohr’s model of the atom.
Ans.Bohr’s model of an atom
1. An atom has a nucleus in the center.
2. Electrons revolve in a definite circular path of fixed energy around the nucleus.
3. The electron can change its shell or energy levels by absorbing or releasing energy.
4. Electron does not radiate energy while moving in discrete orbit.
 |
| Bohr's model of an atom class 9 science |
Q.5 Compare all the proposed models of silicon given in this chapter.
Ans.
Q6. Summaries the rules for the writing of distribution of electrons in various shells for the first eighteen elements.
Ans. Following are the rules for the writing of distribution of electrons in various shells for the first eighteen elements are-
The maximum number of electrons present in a shell is given by the formula- 2n2.
n = orbit number- 1 ,2,3 etc.
Maximum numbers of electrons present in a shell are-
K shell (n =1) = 2n2 = 2 ×11 = 2 electrons
|
L shell (n = 2) = 2n2 = 2× 22 = 8 electrons
|
M shell (n= 3) = 2n2 = 2 ×32 = 18 electrons
|
N shell (n =4) = 2n2 = 2 ×42 = 32 electrons
|
The maximum number of electrons that can be accommodated in the outermost orbit is 8.
Electrons are not accommodated in a given shell unless the inner shells are filled in a step-wise manner.
Q.7 Define valency by taking examples of silicon and oxygen.
Ans. Valency – The combining capacity of an atom is called valency.
Silicon |
The atomic number of silicon = 14 |
Number of electrons present = 14 |
Electronic configuration = K L M = 2 8 4
|
Its outermost shell has 4 electrons which it can share with other atoms to complete its orbit, hence its valency = 4. |
Oxygen |
Atomic number of oxygen = 8 |
Number of electrons present = 8 |
Electronic configuration = K L = 2 6 |
Its outermost shell has 6 electrons. It will gain 2 electrons to complete its octet.Hence, valency = 2.
|
Q.8 Explain with examples (i) Atomic number (ii) Mass number (iii) Isotopes and (iv) Isobars.
Ans. (i). Atomic number – the atomic number of an element is equal to the number of protons in the nucleus of its atom.eg.- carbon has 6 protons so its atomic number is – 6
(ii). Mass number – The mass number is equal to the number of protons and neutrons in its nucleus. It is denoted by ‘A’.. eg. – Carbon has 6 protons and 6 neutrons, so its mass number is 6 +6 = 12
(iii). Isotopes - Isotopes are atoms having the same atomic number but different mass numbers. eg-
(iv) Isobars - Isobars are atoms having the same mass number but different atomic numbers.eg-
Q.9 Na+ has completely filled K and L shells. Explain.
Ans. The atomic number of sodium is 11 and its electronic configuration is 2, 8, 1. Sodium-ion (Na+) is formed by the loss of one electron from the sodium atom.
Na → Na+ + e- |
2,8,1 2, 8 |
KLM K L |
K and L shells of sodium ions have 2 and 8 electrons respectively and are completely filled.
Q.10 If bromine atom is available in the form of, say two isotopes
Ans. Percentage of Br isotope with mass number 79 = 49.7
Percentage of Br isotope with mass number 81 = 50.3
Q.11 The average atomic mass of a sample of an element X is 16.2 μ. What are the percentages of the isotope in the sample?
Ans. Let the percentage of the isotope be x. Hence, the percentage of the isotope is (100- x).
Q.12 If Z = 3, what would be the valency of the element?
Ans. For Z =3, the element is lithium (Li)
Electronic configuration of lithium
Z = 3 = K L
2 1
As the outermost shell has 1 electron. Its valency is 1.
Q.13 Compositions of the nuclei of two atomic species X and Y are given as under:
| X Y |
Protons =
| 6 6 |
Neutrons =
| 6 8 |
Give the mass number of X and Y, what is the relation between the two species?
Ans. Mass number of
X = 6 + 6 = 12
Y = 6 + 8 = 14
Both X and Y contain an equal number of protons but different numbers of neutrons. Hence, X and Y are isotopes.
Q.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 a nucleus.
(b) A neutron is formed by an electron and a proton combining together. Therefore, it is a neutron.
(c)The mass of an electron is about 1/2000 times that of a proton.
(d) Isotope of iodine is used for making tincture iodine, which is used as a medicine.
Ans. (a) False (b) False (c) True (d) False
Q.15 Rutherford’s alpha-particle scattering experiment was responsible for the discovery of
(a) Atomic nucleus
(b) Electron
(c) Proton
(d) Neutron.
Ans. (a) Atomic nucleus.
Q.16 Isotopes of an element have:
(a) The same physical properties
(b) Different chemical properties
(c) Different number of neutrons
(d) Different atomic numbers.
Ans. (c) A different number of neutrons.
Q.17 Number of valence electrons is Cl- ion are:
(a) 16
(b) 8
(c) 17
(d) 18
Ans. As the electronic configuration of chlorine Cl (Z = 17) is
K L M
2 8 7
It gains 1 electron in the outermost shell to complete its octet. Hence, valency is 7 + 1 = 8.
Q.18 Which one of the following is a correct configuration of sodium?
(a) 2, 8
(b) 8, 2, 1
(c) 2, 1, 8
(d) 2, 8, 1
Ans. (d) Atomic number of sodium = 11
Its electronic configuration
K L M
2 8 1
Q.19 Complete the following:
Atomic number | Mass number | Number of Neutrons | Number of Protons | Number of Electrons | Name of the Atomic Species |
9 16 - - - | - 32 24 2 1 | 10 - - - 0 | - - 12 1 1 | - - - - 0 | - Sulphur - - - |
Ans.
Atomic number | Mass number | Number of Neutrons | Number of Protons | Number of Electrons | Name of the Atomic Species |
9 16 12 1 1 | 19 32 24 2 1 | 10 16 12 1 0 | 9 16 12 1 1 | 9 16 12 1 0 | Fluorine Sulphur Magnesium Deuterium Protium |
Important points of NCERT Solutions Class 9 Science Chapter 4
so here you are provided important points
of NCERT solutions class 9 science chapter 4 which will be so useful for you to
understand the chapter 4 structure of an atom,
so read them thoroughly and note down.
1. According to Dalton’s atomic theory, the atom is considered to be the smallest indivisible constituent of all matter. This theory could explain the law of conservation of mass. Law of constant composition and law of multiple proportions. So further experiments showed that an atom is the smallest particle but it is made up of even the smallest particles electrons, protons, and neutrons.
2. J.J. Thomson discovered the electron.
3. Sir J.J. Thomson discovered that when very high voltage was passed across the electrodes in the cathode ray tube, the cathode produced rays that travel from cathode to anode and were called cathode rays. It shows that the rays were made upstream of negatively charged particles called electrons. The discovery of electrons meant that the atom is not indivisible as believed by Dalton and others.
4. J.J. Thomson proposed that electrons are embedded in a positive sphere.
5. E. Goldstein discovered anode rays by using a perforated cathode (with holes in it) in the discharge tube filled with air at very low pressure. The discovery of anode rays established the presence of positively charged particles protons in an atom.
6. Rutherford’s alpha-particle scattering experiment led to the discovery of the atomic nucleus.
7. Rutherford’s model of the atom proposed that a very tiny nucleus is present inside the atom and electrons revolve around the nucleus. The stability of the atom could not be explained by this model.
8. Rutherford’s model however failed as it could not explain the stability of the atom, the distribution of electrons, and the relationship between the atomic mass and atomic number.
9. According to Thomson’s Plum pudding model, atoms can be considered as a large sphere of uniform positive charge with a number of small negatively charged electrons scattered throughout it.
10. Neil’s Bohr’s model of the atom was more successful. He proposed that electrons are distributed in different shells with discrete energy around the nucleus. If the atomic shells are complete, then the atom will be stable and less reactive.
11. Chadwick discovered the presence of neutrons in the nucleus of an atom. So, the three subatomic particles of an atom are – electron, proton, and neutron. Electrons are negatively charged particles, protons are positively charged particles and neutrons have no charge on them, they are neutral.
12. The mass of electrons is about 1/2000 times the mass of a hydrogen atom. The mass of a proton and neutron is taken as one unit each.
13. Shell of an atom are designated as K, L, M, N…
14. Valency is the combining capacity of an atom.
15. The atomic number of an element is the same as the number of protons in the nucleus of its atom.
16. The mass number of an atom is equal to the number of nucleons in its nucleus.
17. Isotopes are atoms of the same element, which have different mass numbers.
18. Isobars are atoms having the same mass number but different atomic numbers.
19. Elements are defined by the number of protons they possess.
You must know facts about NCERT Class 9 Science Chapter 4 Solutions
1. The e/m ratio for the particles in the cathode rays was found to be the same irrespective of the nature of the cathode or the nature of the gas taken in the discharge tube, these show that the electrons are the basic constituent of all atoms.
2. An electron is a fundamental particle of an atom carrying one unit negative charge and having mass nearly equal to 1/1840th of mass of an atom of hydrogen.
3. A proton is a fundamental particle of an atom carrying one unit positive charge and having nearly equal to the mass of an atom of hydrogen.
4. The phenomenon of radioactivity that is the spontaneous emission of rays from atoms of certain elements also proved that the atom was divisible.
5. On the basis of Rutherford’s atomic model, he could predict the size of the nucleus. he estimated that the radius of the nucleus was 1/104 times smaller than that of the radius of the atom.
6. Nuclear model of an atom can be compared with the solar system. In an atom, an electron revolves around the nucleus in just the same way as the planets revolve around the sun. Rutherford’s nuclear model of the atom is known as the Planetary model of the atom.
7. The electronic configuration of sodium in 2,8,1. The loss of the valence electron, so sodium is a very reactive element.
8. The electronic configuration of fluorine is 2,8,7. So fluorine has one less electron than needed to fill the valence shell completely. The gain of one electron would produce a stable .so fluorine is a chemically very reactive element.
9. J.J. Thomson (1856-1940) a British physicist, was born in Cheetham Hill, a suburb of Manchester, on 18 December 1856. He was awarded the Nobel prize in Physics in1906 for his work on the discovery of electrons. He directed the Cavendish for 35 years and seven of his researches assistants subsequently won Nobel prizes.
10. Rutherford (1871-1937) was born at Spring Grove on 30 August 1871. He was known as the ‘father of nuclear physics. He is famous for his work on radioactivity and the discovery of the nucleus of an atom with the gold foil experiment. he got the Nobel prize in chemistry in 1908.
11. Neils Bohr (1885-1962) was born in Copenhagen on 7 October 1885. He was appointed professor of physics at Copenhagen University in 1916. He got the Nobel prize for his work on the structure of atoms in 1922. Among professor Bohr’s numerous writings. Three books- (i) The theory of spectra and atomic constitution (ii) Atomic theory (iii) The description of nature.
Important Oral Questions- Answers of Ch 4
Class 9 Science NCERT Solutions
Now you have understood the key points of Ch 4 Class 9 Science NCERT Solutions, that’s why you are given
some important oral questions- answers of chapter 4 class 9 science, which are
very useful for your internal assessments. you are advised to learn and
practice them all.
Question -1- Helium has an atomic mass of 4u and 2 protons in its nucleus. how many neutrons does it have?
Answer- 2 neutrons
Question- 2-What is an Ion?
Answer- A charged atom is called an ion.
Question- 3-What is the principle of calculation of valency?
Answer- The number of electrons in the valence shell of an atom that actually takes part in the formation of a chemical bond is equal to its valency.
Question-4-What is a cation?
Answer- A positively charged ion is called a cation.
Question- 5- What is a valence shell?
Answer- The outermost shell of an atom is called its valence shell.
Question- 6-What are canal rays?
Answer- The positive rays reduced in the discharged tube are called canal rays.
Question-7- Name the shell which is closest to the nucleus of the atom.
Answer- K shell
Question- 8-What is the net charge on an atom?
Answer- Zero
Question- 9-Name an isotope used to detect the presence of tumors.
Answer- Arsenic 74
Question- 10-What is the importance of e/m?
Answer- e/m confirms that electron is a common constituent of all types of substances.
Question-11- What is the mass of an electron?
Answer- 9.109 ×10-31 kg
Question-12-Which isotope of carbon is used in radiocarbon dating?
Answer- C-14
Question- 13-What is mass number?
Answer- The sum of the numbers of protons and neutrons present in the nucleus of an atom is equal to the mass number.
Question- 14-What determines the chemical properties of elements?
Answer- The number of electrons and their arrangement in different shells of the atom determines the chemical properties of elements.
Question-15- Which shell has the lowest energy?
Answer- K shell
Question-16- What are orbits?
Answer- Electrons revolve around the nucleus in defined circular paths, these circular paths are called orbits.
Suggested Topics for Internal Assessment and Examination of Chapter 4 Science Class 9 NCERT Solutions
You have been suggested some important
topics of chapter 4 science class 9 NCERT solutions for your better preparation
for upcoming examinations so prepare notes on them.
1. Electronic configuration
2. Arrangement of electrons in different shells. Bohr- Bury scheme.
3. What are energy levels?
4. Elements with stable electronic configuration
5. Elements with one electron in the outermost shell
6. Electronic configuration of atoms involving only K shell.
7. Electronic configuration of elements with atomic numbers 1 to 18.
8. Electronic capacity of an energy level or shell-2n2
9. Discovery of protons and canal rays
10. Structure of atom
11. Experimental study of Rutherford’s alpha particle experiment
12. Application of isotopes
13. Bohr’s model of an atom
14. Rutherford’s model of atom and drawbacks
15. Find Mass of electron
Frequently asked Questions
1. What is
atomic structure short answer?
An atom is the smallest particle that consists of sub-particles named electron, proton, and neutron.
2. What is atom Class 9 learn CBSE?
In CBSE class 9 fourth chapter is the structure of the
atoms. Different scientists gave the model of an atom. Basically, an atom is a
very tiny particle that can’t be seen with naked eyes. an atom consists of
subatomic particles – electrons, protons, and neutrons
3. What isWhere is the electron found and what is its
charge?
Electron is found in an atom and revolve around the nucleus
in certain energy levels or shells.
4. What is an electron and who discovered it in class 9?
Electrons are negatively charged particles and J.J. Thomson
discovered electrons. In class 9 an experiment has been described performed by Thomson.
5. What observation led Rutherford to conclude that
most of the space inside the atom is hollow?
Rutherford performed an alpha particle experiment, in which
a stream of alpha particles from radioactive elements or substances was directed
on a thin gold foil. Most of the alpha particles passed the foil straight so he
observed that most of the space inside the atom is hollow.
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