Class-8th The Structure of the Atoms Essential Chemistry Solutions Ch-4

Class-8th The Structure of the Atoms Essential Chemistry Bharti Bhawan  Solutions Chapter-4. We Provide Step by Step Answer of Objective, True False , Match the following , Short / Long Answer Type of Exercise-4 The Structure of the Atoms. Visit official Website CISCE for detail information about ICSE Board Class-8.

Class-8th The Structure of the Atoms Essential Chemistry Solutions Ch-4 Bharti Bhawan

Board ICSE
Publications Bharti Bhawan
Subject Chemistry
Class 8th
Chapter-4 The Structure of the Atoms
Book Name Essential
Topics Solution of Objective, True False , Match the following , Short / Long Answer Type Questions
Academic Session 2021-2022

 Short-Answer Type Questions

Solutions of Bharti Bhawan Publishers for ICSE Class-8th Essential Chemistry Ch-4 The Structure of the Atoms 

Page 42

Question 1 : 

What name was given by Kanad to the tiny particles that matter is made up of ?

Answer :  Acharya Kanad thus named that indivisible tiniest of tiny particles of matter as ‘Parmanu’ or ‘anu’. We commonly call this indivisible tiniest of tiny particles of matter as atoms

Question 2 : 

Answer the following on the basis of Dalton’s atomic theory.

(a) Are atoms divisible?

(b) Do atoms of the same element have the same weight?

(c) Do atoms of different elements have the same weight.

(d) What are the particles that take part in a chemical reaction?

Answer :  

(a) According to Dalton atomic theory, atoms are divisible particles and can be created in a chemical reaction. According to Dalton, an atom can be further subdivided into protons, neutrons and electrons.

(b)

Atoms of the same chemical element do not always have the same mass because, although the number of protons in the nucleus is the same for all atoms of the same element, the number of neutrons is not. Most elements as they occur naturally on earth are mixtures of several isotopes.

(c)

The molar mass of an atom is simply the mass of one mole of its identical atoms. However, most of the chemical elements are found on earth not as one isotope but as a mixture of isotopes, so the atoms of one element do not all have the same mass

(d)

The correct answer is Only electrons participate in chemical reactions. Electrons are the negatively charged particles of an atom that are involved in chemical reactions.

Question 3 : 

Name the particles that constitute cathode rays.

Answer :  Cathode rays are made up of electrons—the fundamental negatively charged particles.

Question 4 : 

What are anode rays made of?

Answer :  An anode ray (also positive ray or canal ray) is a beam of positive ions that is created by certain types of gas-discharge tubes. They were first observed in Crookes tubes during experiments by the German scientist Eugen Goldstein, in 1886.

Question 5 : 

Give the word equation that led to the discovery of neutrons.

Answer :  Chadwick repeated the creation of the radiation using beryllium to absorb the alpha particles: 9Be + 4He (α) → 12C + 1n. These particles were neutrons.

Question 6 : 

What are the relative masses and unit charges of the electron, proton and neutron?

Answer :

Subatomic particle Relative mass Relative charge
Proton 1 +1
Neutron 1 0
Electron 0.0005 -1

 

Question 7 : 

Who discovered the nucleus ?

Answer :  Rutherford

Question 8 : 

Which fundamental particles constitute the nucleus of an atom?

Answer :  The nucleus of an atom consists of neutrons and protons,

Question 9 : 

The nucleus of an atom of which element does not contain neutrons?

Answer : The hydrogen (H) atom does not have any neutrons in its tiny nucleus.

Question 10 : 

Where are electrons placed in an atom? Are they stationary?

Answer :  The electrons are placed around the nucleus in the atom. NO they are not stationary.

Question 11 : 

What particles will be formed if an electron is transferred from a sodium atom to that of chlorine?

Answer :  When a sodium atom transfers an electron to a chlorine atom, forming a sodium cation (Na+) and a chloride anion (Cl), both ions have complete valence shells, and are energetically more stable.

Question 12 : 

Give the nuclide symbols of sodium (atomic number = 11, mass number = 23) and phosphorus (atomic number = 15, mass number = 31).

Answer :  Sodium = Na and Phosphorus = P


 Long-Answer Type Questions

Solutions of Bharti Bhawan Publishers for ICSE Class-8th Essential Chemistry Ch-4 The Structure of the Atoms 

Page 43

Question 1: 

Describe the cathode-ray experiment of Sir J J Thomson that led him to conclude that cathode rays are made up of negatively charged particles.

Answer :  In the late 19, start superscript, start text, t, h, end text, end superscript century, physicist J.J. Thomson began experimenting with cathode ray tubes. Cathode ray tubes are sealed glass tubes from which most of the air has been evacuated. A high voltage is applied across two electrodes at one end of the tube, which causes a beam of particles to flow from the cathode (the negatively-charged electrode) to the anode (the positively-charged electrode). The tubes are called cathode ray tubes because the particle beam or “cathode ray” originates at the cathode. The ray can be detected by painting a material known as phosphors onto the far end of the tube beyond the anode. The phosphors spark, or emit light, when impacted by the cathode ray.

The properties of cathode ray-

  • The cathode ray is composed of negatively-charged particles.
  • The particles must exist as part of the atom, since the mass of each particle is only 1, divided by, 2000, fraction of the mass of a hydrogen atom.
  • These subatomic particles can be found within atoms of all elements.

Question 2: 

Explain how cathode rays and anode rays are produced in a discharge tube.

Answer :  Inside the vacuum tube there are positive and negative electrodes. The positive electrode is called anode and the negative electrode is called cathode. When a high voltage is applied between the cathode and the anode, the electrons are accelerated at high speed from the cathode to the anode.

Question 3: 

What observations did Rutherford make in his a-particle scattering experiment? How did he interpret them to arrive at the nuclear model of the atom?

Answer :  Since some ?-particles were deflected back it means they must got striked to some heavy particles. these heavy particles were called as NUCLEUS. ->Thus according to Rutherford’s Model the atom consists of two parts, first is the Nucleus, and second is the extra nuclear part.


 Objective Type Questions

Solutions of Bharti Bhawan Publishers for ICSE Class-8th Essential Chemistry Ch-4 The Structure of the Atoms 

Page 33

Choose the correct option.

Question 1: Which of the following is an electrically neutral particle?

(a) The electron

(b) The proton

(c) The neutron

(d) The a-particle

Answer :  (c) The neutron

Question 2: The particle with-1 unit of electrical charge is

(a) the electron

(b) the proton

(c) the neutron

(d) an α-particle

Answer :  (a) the electron

Question 3: Which of the following particles will pass undeviated  through an electric field?

(a) Electrons

(b) Protons

(c) Neutrons

(d) a-particles

Answer :  (c) Neutrons

Question 4: The atom of which of the following elements has only one proton?

(a) Hydrogen

(b) Helium

(c) Sodium

(d) Neon

Answer :  (a) Hydrogen

Question 5: Which of the following atoms will have the same number of electrons, protons and neutrons?

(a) 12C6

(b) 23Na11

(c) 31P15

(d) 35Cl17

Answer :  (a) 12C6

Question 6: Which of the following atoms has an odd number of neutrons?

(a) 11B5

(b) 14N7

(c) 23Na11

(d) 31P15

Answer :  (b) 14N7


Fill in the blanks. 

(Solutions of Bharti Bhawan Publishers for ICSE Class-8th Essential Chemistry Ch-4 The Structure of the Atoms )

(Page 44)

1. The mass of the cathode-ray particles is …….fixed……… (fixed / variable)

2. The mass of the anode-ray particles is …….fixed…… (fixed / variable)

3. The mass of atoms, except that of hydrogen……can…………… be explained without considering neutrons (can / cannot)

4. An atom has the same number of electrons, protons and neutrons if the mass number is ………double…. the atomic number of the element. (double / triple)

5. Complete the following table.

Elements Z A Electrons Protons Neutrons
Na 11 23 11 11 12
Al 13 27 13 13 14
Si 14 28 14 14 14
S 16 32 16 16 16
Ar 18 40 18 18 22

 


Write T for true and F’ for false for the following statements.

(Solutions of Bharti Bhawan Publishers for ICSE Class-8th Essential Chemistry Ch-4 The Structure of the Atoms )

1. An atom must contain the same number of protons as neutrons.  False

2. An electron is an extranuclear particle.  False

3. An a-particle is positively charged.  True

4. Cathode rays are a stream of electrons.  True

5. Anode rays are a stream of protons.  True

-: End ofClass-8th The Structure of the Atoms Essential Chemistry Bharti Bhawan Solutions Chapter-4.  :-


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