Question

2. Compare all the models of atom given in the chapter “structure of the atom”. Give drawbacks

of models also.class 9​

Answer 1

Answer:

the draw back of 1 st model is that it is unstable

mass back of second model.is that it have unstable electrons

Answer 2

Answer:

1) Thomson's model of the atom

When J.J. Thomson proposed his model of the atom in 1903, then only electrons and protons were known to be present in the atom. According to Thomson's model of the atom:

i) An atom consists of a sphere (or ball) of positive charge with negatively charged electrons embedded in it.

ii) The positive and negative charges in an atom are equal in magnitude, due to which an atom is electrically. It has no overall positive or negative charge.

We can also compare Thomson's model of the atom to a watermelon. The red, edible part of watermelon represents the sphere of positive charge whereas the black seeds embedded in watermelon are like the electrons. Although, Thomson's model of atom explained the electrically neutral nature of atom.

2) Rutherford's model of the atom

On the basis of alpha particle scattering experiment, Rutherford gave a nuclear model of the atom. Rutherford's model of atom (or structure of atom) can be described as follows:

i) The electrostatic attraction between the positively charged nucleus and negatively charged electrons holds the atom together.

ii) An atom is electrically neutral. This is because the number of protons and electrons in an atom is equal.

iii) Most of the atom is empty space.

Drawbacks of Rutherford's Model of The Atom

A major drawback of Rutherford's model of the atom is that it does not explain the stability of the atom. In the Rutherford's model of an atom, the negatively charged electrons are revolving around the positively charged nucleus in circular paths. Now, we know that if an object moves in a circular path, then it's motion is said to be accelerated. This means that the motion of an electron revolving around the nucleus is accelerated. According to the electromagnetic theory of physics, if a charged particle undergoes accelerated motion, then it must radiate energy (or lose energy) continuously.

3) Bohr's model of the atom

The Bohr's model of atom can be described as follows:

i) An atom is made up of three particles: electrons, protons and neutrons.

ii) The protons and neutrons are located in a small nucleus at the centre of the atom.

iii) The electrons revolve rapidly round the nucleus in fixed circular paths called energy level or shells.

iv) There is a limit to the number of electrons which each energy level (or shell) can hold.

v) Each energy level (or shell) is associated with a fixed amount o energy.

vi) There is no change in the energy of electrons as long as they keep revolving in the same energy level, and the atom remains stable.

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