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

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.

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.

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.

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.