NCERT Solutions for Class 9 Science Chapter 4
NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom Exercise and Intext question answers in PDF form to free download. All the solutions are updated for new academic session 2020-2021 based on latest CBSE Syllabus 2020-21.Class 9 Science chapter 4 Intext questions given on Page 43 or Page 49 or Page 50 or Page 52 or Page 53 and Exercises in English Medium are available. You can download these solutions from पेज 53 के उत्तर or पेज 56 के उत्तर or पेज 57 के उत्तर or पेज 58 के उत्तर or पेज 59 के उत्तर or पेज 60 के उत्तर and अभ्यास के प्रश्न उत्तर to study online or in PDF form. NCERT Solutions 2020-21 and Offline Apps for all other subjects based on latest CBSE Syllabus 2020-21 are also available to download.
NCERT Solutions for Class 9 Science Chapter 4
|Subject:||Science – विज्ञान|
|Chapter 4:||Structure of the Atom|
9th Science Chapter 4 Answers in English & Hindi Medium
NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom Intext Questions and chapter end exercise question answers are given below to free download. All the solutions are free to download without any registrations or login. We have updated all the contents on the basis of user’s suggestions and Feedback received from last academic session.
9th Science Chapter 4 Answers in English Medium
9th Science Chapter 4 Answers in Hindi Medium
9th Science Chapter 4 Answers in PDF Form
Is atomic number of an atom always equal to the number of electrons?
No, it is the case when the atom has no charge. In case of cation (positively charged), atomic number is more than the number of electrons and in case of anion (negatively charged), it is less than the number of electrons.
Nucleus of an atom has positive charge on it. Establish.
This can be established on the basis of Rutherford scattering experiment. Since some alpha particles were repelled by the nucleus of the atom, it is expected to have the same charge as on alpha particles. Therefore, nucleus of an atom has positive charge.
Were neutrons known at the time Rutherford performed the scattering experiment?
No, these were discovered later on by Chadwick in 1931 whereas scattering experiment was performed by Rutherford in 1911.
Why are isotopes of an element chemically similar?
Isotopes of an elements have same number of electrons and therefore, same value shell electronic distribution. Since the chemical properties of the atoms are related to valence shell configurations, the isotopes are chemically similar.
Why do elements which exist as isotopes have fractional atomic masses?
The different isotopes of an element differ in their mass number as well as atomic masses. In order to represent the atomic mass of the element, we have to consider average of the atomic masses of the different isotopes and also the ratio in which these are present. In most of the cases, the average comes out to be in fraction. Therefore, these elements have fractional atomic masses.
Why is a proton not a universal particle like electron?
A proton is the positively charged residue left when hydrogen gas is enclosed in the in the discharge tube. For the other gases, the positive residues formed contain different number of protons. Therefore, proton is not a universal particle like electron.
Questions for Practice on 9th Science Chapter 4
An electron is regarded as a universal particle. Explain.
The value of charge (e) and mass (m) of the electron always remain the same whatever may be the source of their emission. In the discharge tube, the electrons may be emitted either from the cathode or form the gas enclosed in the discharge tube. Whatever may be the metal which forms the cathode or the gas present in the discharge tube, these values remain the same. Therefore, electron is regarded as a universal particle.
Why do the element helium, neon and argon have zero valency?
Helium has two electrons in its only energy shell (K-shell). The other two elements have eight electrons in their valence shells. Since these are the maximum number of electrons which the atoms of these elements can have therefore, they do not have any urge or desire to take part in chemical combination. These elements are known as zero valent elements. They have therefore, valency equal to zero.
Important Questions on 9th Science Chapter 4
For example calcium, atomic number 20 and argon, atomic number 18.
The number of electrons in these atoms is different, but the mass number of both these elements is 40. That is, the total number of neutrons is the same in the atoms of this pair of elements.
L कोश में इलेक्ट्रॉनों की कुल संख्या = 8
इसलिए, कुल इलेक्ट्रॉन = 2 + 8 = 10
अतः, उस परमाणु में इलेक्ट्रॉनों की संख्या 10 होगी।
अतः, परमाणु की परमाणु संख्या = 8
(b) परमाणु का आवेश = प्रोटॉनों की संख्या – इलेक्ट्रॉनों की संख्या = 8 – 8 = 0
अतः, परमाणु पर कोई आवेश नहीं है और परमाणु उदासीन है।