NCERT Solutions for Class 9 Science Chapter 4: Structure Of The Atom

Content Curator

The NCERT Solutions for class 9 Science Chapter 4 Structure Of The Atom have been provided in the article below. Some of the Class 9 Science Chapter 4 important concepts include:

NCERT Solutions for Class 9 Science Chapter 4

Download: NCERT Solutions for Class 9 Science Chapter 4 pdf

Important Topics in Class 9 Science Chapter 4 Structure of the Atom

Structure of Atom consists of three basic particles: Electrons, Protons, and Neutrons. Nucleus is the center of the atom and contains protons. Protons are positively charged, whereas Neutrons have no charge. In absence of electrical charge, the neutron is not repelled by a cloud of electrons or by a nucleus. Thus, it becomes a useful tool for probing the structure of atoms. Outermost parts of atoms are called Electron Shells and contain negatively charged electrons.

Atomic Number

Atomic number can be expressed by the number of protons or electrons present in the atom. Atomic number is responsible to determine the type of an element. It is represented by the letter Z.

Example: Calculate the mass number of a given element which has an atomic number of 15 and a total number of protons of 15.

Solution: As we already know the formula, the mass number can be determined,
Thus, Number of Protons + Number of Electrons = Mass Number
= 15 + 15 = 30

Mass Number

Mass number, or atomic mass number, of an element can be defined as the total number of protons found in the atom of an element. The mass number of elements is important because it helps determine atomic mass.

The Formula of Mass Number: Mass number = The Atomic mass number + the total number of neutrons

Subatomic Particles of an Atom

Subatomic particles are those that help compose atoms. These are the constituent units of all matter, including Electrons, Protons and Neutrons.

Example: Name and define the three Subatomic Particle of an Atom.

Solution: The three primary subatomic particles are Electrons, Protons, and Neutrons. Electrons are known for its negatively charged particles, while protons are positively charged. Meanwhile, neutrons are neutral as because they do not carry any charge.

Proton Mass

Protons are stable subatomic particles possessing positive charge. It is considered equal in magnitude to a unit of electron charge, alongside a rest mass of 1.67262 × 10⁻²⁷ kg. Proton Mass cn be represented using the sign m_p.

Example: How is Proton Mass calculated?

Solution: Proton Mass can be evalutated using three steps:

These are the three methods:

Theoretical calculation
Via atomic molar mass (which is a measure of atomic mass)
By estimating and comparing the charge/mass with electrons

Check Out:

Chapter Related Links
Rutherford Model of an Atom	Valency	Chemical Formula
Atoms MCQs	Size of the Nucleus	Isotopes and Isobars
Valence Bond Theory	Valence Electrons	Isotopes
Writing Chemical Formulae	Atomic Mass Formula

Also Check:

Important Science Study Guides
Named Reactions	Physics Constants	Difference between in biology
Difference between in chemistry	Difference between in physics	Periodic Table

CBSE X Related Questions

1.
Which structure in a leaf is mainly responsible for gaseous exchange?
- Xylem
- Stomata
- Phloem
- Cuticle
View Solution
2.
(a) Study the given electric circuit in which 2 A electric current is flowing between points X and Y.

(i) Using the battery, key, voltmeter and ammeter in this given electric circuit, redraw a circuit diagram in which 2 \(\Omega\) and 4 \(\Omega\) resistors are connected between X and Y in parallel combination.
(ii) Circuit drawn by you, in which resistors are connected in parallel combination, calculate the electric current flowing through 4 \(\Omega\) resistor.
View Solution
3.
What is the function of diaphragm in human respiratory system ? Where is it present in human body ?
View Solution
4.
Briefly mention the steps in double-circulation through human heart.
View Solution
5.
Due to change in length and area of cross-section of a conductor, resistance of conductor changes while resistivity does not change. Why ?
View Solution
6.
The reasons for excessive generation of wastes are:
(i) Use and throw policy.
(ii) Increased availability of packaged food.
(iii) Increased construction wastes.
(iv) Non-sorting of dry and wet wastes
- (i), (iii) and (iv)
- (i), (ii) and (iii)
- (i), (ii), (iii) and (iv)
- (ii), (iii) and (iv)
View Solution