Answer the following:
1.How were cathode rays discovered by Thomson? Describe with the help of an experiment.
2. Define the terms atomic number and mass number.How are they related to each other?In which case the atom of the element has same number of protons and electrons?
3.Discuss the main features of Rutherford scattering experiment.What are the limitations of this model of the atom?
4. How do neutrons and protons differ in characteristics?
5.Write the main postulates of Bohr-Bhury scheme.
Answers
- Summary. J.J. Thomson's experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons. Thomson proposed the plum pudding model of the atom, which had negatively-charged electrons embedded within a positively-charged "soup."
- The mass number of an atom is equal to the number of protons plus the number of neutrons that it contains. In other words, the number of neutrons in any atom is its mass number minus its atomic number. Although all atoms of a given element must have the same atomic number, they need not all have the same mass number.
- Although the Rutherford atomic model was based on experimental observations it failed to explain certain things. Rutherford proposed that the electrons revolve around the nucleus in fixed paths called orbits. ... So Rutherford model was not in accordance with Maxwell's theory and could not explain the stability of an atom.
- Protons are a type of subatomic particle with a positive charge. Protons are bound together in an atom's nucleus as a result of the strong nuclear force. Neutrons are a type of subatomic particle with no charge (they are neutral).
- Electrons revolve around the nucleus in different energy levels or shells and each shell is associated with definite energy. The energy of the K shell is the least while those of L, M, N and O shells increases progressively. ... 3rd energy level is M shell4th energy level is N shell and so on.
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Explanation:
1.Thomson's experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons. Thomson proposed the plum pudding model of the atom, which had negatively-charged electrons embedded within a positively-charged "soup."
The ray originates at the cathode and passes through a slit in the anode. The cathode ray is deflected away from the negatively-charged electric plate, and towards the positively-charged electric plate. The amount by which the ray was deflected by a magnetic field helped Thomson determine the mass-to-charge ratio of the particles.
2.The mass number of an atom is equal to the number of protons plus the number of neutrons that it contains. In other words, the number of neutrons in any atom is its mass number minus its atomic number. Although all atoms of a given element must have the same atomic number, they need not all have the same mass number.
3.On the basis of his experiment, Rutherford put forward the model of an atom, which had the following features: There is a positively charged centre in an atom called the nucleus. Nearly all the mass of an atom resides in the nucleus. The electrons revolve around the nucleus in well-defined orbits.
The major limitation of Rutherford’s model of the atom is that it does not explain the stability of the atom. As we know now, when charged bodies move in circular motion, they emit radiations. This means that the electrons revolving round the nucleus (as suggested by Rutherford) would lose energy and come closer and closer to nucleus, and a stage will come when they would finally merge into the nucleus. This makes the atom unstable, which is clearly not the case. The electrons do not fall into the nucleus, atoms are very stable and do not collapse on their own.
It didn’t explain about the arrangement of electron inside atom.
4.Protons are positively charged, neutrons are uncharged and electrons are negatively charged. The negative charge of one electron balances the positive charge of one proton. Both protons and neutrons have a mass of 1, while electrons have almost no mass.
(or)
Protons are a type of subatomic particle with a positive charge. Protons are bound together in an atom's nucleus as a result of the strong nuclear force. Neutrons are a type of subatomic particle with no charge (they are neutral).
5 Electrons revolve around the nucleus in different energy levels or shells and each shell is associated with definite energy. The energy of the K shell is the least while those of L, M, N and O shells increases progressively. ... 3rd energy level is M shell4th energy level is N shell and so on.