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Lakhmir Singh Chemistry Class 9 Solutions Chapter 4 - Structure Of The Atom

Last updated date: 16th Apr 2024
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An overview of Lakhmir Singh Class 9 Chemistry Solutions Chapter 4 - Structure of the Atom

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Summary of Chapter 4- Structure of the Atom Chemistry Class 9

This Chapter elaborates on the structure of the Atom. Atoms are made of a nucleus and orbits, the nucleus contains Protons and Neutrons and the orbits contain the Electrons. The number of Protons, Electrons, and Neutrons varies with the element the Atom belongs to. 

In the introduction, the description of an Atom and its subatomic parts is given.

The Cathode Ray Experiment

The experiment decodes how electrons were discovered. The cathode ray experiment was carried out by J.J Thomson. The cathode ray tube was vacuum-sealed and was subjected to high voltage and electricity flow. The experiment successfully depicted how the Atom was not one entire part but was made up of subatomic parts.

Thomas model of an Atom

Thomas was the first scientist to come up with the concept of an Atom made of two parts, one part was negatively charged and the other part was positively charged. Thomas proposed the Atom be similar to a watermelon. As per him, the red part was the positively charged part, while the black colored seeds were the negatively charged part. Later on, it was found that he wasn’t entirely right but he was correct about the positive and negative parts of the Atom.

Radioactivity and Radioactive elements

The Chapter also gives a brief introduction to Radioactivity. When a nucleus of an Atom is unstable (having a different number of neutrons and protons) it emits out certain particles spontaneously, this phenomenon is known as radioactivity. Those particles can be Alpha, Beta, or Gamma particles. 

Rutherford’s experiment 

Rutherford experimented to prove how the positive charge in an Atom is not distributed in the entire Atom and how the Atom is mostly empty. In the experiment, he bombarded Alpha particles on a gold foil to prove that the positive charge in an Atom is concentrated in a very small place inside the Atom.

Bohr’s model of an Atom

Bohr explains how each orbit has energy shells. The model also clears out how the electrons do not radiate out any emission. Bohr designated every energy level as K, L, M, N shells. The lowest energy level of an electron is known as ground level. An electron emits or absorbs energy as it moves through different energy levels, this depends on whether it moves to a higher energy shell or lower energy shell.

FAQs on Lakhmir Singh Chemistry Class 9 Solutions Chapter 4 - Structure Of The Atom

1. What are the different types of Radioactive particles mentioned in Lakhmir Singh Class 9 Chemistry Solutions Chapter 4 - Structure of the Atom - Free PDF Download?

Radioactivity is a state of an Atom when an Atom continuously decomposes certain particles to attain a stable nucleic state. There are various kinds of particles that are emitted in the process. The first kind is Alpha particles, these particles are the largest. Alpha particles have only a positive charge, they contain two protons and two neutrons. As they are the largest, their penetration power is also the least. Beta particles on the other hand are high-energy electrons, they have the highest penetrating power. Gamma rays are also emitted from radioactive substances, these rays are harmful and have no charge.

2. What is the drawback of Rutherford’s model mentioned in Lakhmir Singh Class 9 Chemistry Solutions Chapter 4 - Structure of the Atom - Free PDF Download?

Rutherford presented the model of an Atom with the help of his alpha particle experiment. Rutherford explained how there was a positive charge in the nucleus and circular orbits around it. He said the electrons were revolving around the nucleus and were placed in the orbits. It was not possible for the electrons to not experience acceleration if they revolved around. The acceleration would lead to electron radiating energy. This would probably lead to electrons falling into the nucleus. If all of that did happen, the Atoms would not be in the form we know them to be. This model failed to explain why this did not happen and how the Atoms were stable having both positive and negative charges.

3. What is Valency according to Lakhmir Singh Class 9 Chemistry Solutions Chapter 4 - Structure of the Atom - Free PDF Download?

Every Atom has a certain number of electrons in its outermost orbit. The number of such electrons in a particular orbit is known as its valency. The interactions of an element with other elements and its chemical activities are highly defined by its valency and the number of valence electrons it has. When the outermost orbit of an Atom has zero electrons, its valency is zero and the chemical activity is almost nil. Valency can also be defined as the number of electrons an Atom will need to give up or take to attain stability.

4. What are isotopes according to Lakhmir Singh Class 9 Chemistry Solutions Chapter 4 - Structure of the Atom - Free PDF Download?

When an element has two different types of Atoms and they have the same Atomic number and position in the periodic table, they are known as Isotopes. The Atomic number of isotopes is the same but there is a difference in the Atomic mass. Isotopes have a different number of neutrons and the same number of protons. Isotopes have the same valency as the number of electrons is the same. The isotopes have the same chemical properties. A good example of isotopes is Carbon, Carbon 12 and Carbon 14 are isotopes, one of them has 6 neutrons and the other has 8 neutrons.

5. How should I prepare for the theories of Chapter 4 Chemistry CBSE Class 9 using Lakhmir Singh Class 9 Chemistry Solutions Chapter 4 - Structure of the Atom - Free PDF Download?

To prepare for chemistry theories and to score well in your chemistry exam you must have your basics in the subject clear. Read all the theories properly and note down the main points. Try to memorize the names of scientists that made a significant discovery. Remember each theory and its drawbacks. New theories are often given to clarify and overcome the drawbacks of the previous theory. It is necessary to know the specific diagrams given in the Chapter. For instance, you must know the diagram of a cathode ray tube. Nothing is better than revision. Keep on revising every theory every week. These solutions can be downloaded free of cost from the official website of Vedantu and app.