Question

Question 5 Compare all the proposed models of an atom given in this chapter.

Class 9 - Science - Structure of the Atom Page 54

Answer 1

Heya,

Thomson's model of an atom:
1. An atom consists of a sphere of positive charge with negatively charged electrons embedded in it.
2. The positive and the negative charges in an atom are equal in magnitude due to which an atom is electrically neutral.

Rutherford's model of an atom:
1. There is a positively charged, highly densed centre in an atom called the nucleus. Nearly the whole mass of an atom resides in the nucleus.
2.The electrons revolve around the nucleus in circular path.
3. The size of the nucleus is very small compared to the size of an atom.

Bohr's model of an atom:
1.An atom is made up of 3 particles electrons, protons and neutrons. Due to the presence of equal number of electrons and protons, atom on the whole is electrically neutral.
2. The protons and neutrons are located inside the nucleus due to which nucleus is positively charged.
3. The electrons revolve around the nucleus in fixed paths called orbots or shells or energy levels. The energy levels are represented as K,L,M,N or 1,2,3,4,5,.....
4. There is a limit to the number of electrons each energy level can hold. It is given by the formula 2n^2 where n is the orbit number .
5. Each energy level is associated with fixed amount of energy, the shell nearest to the nucleus having minimum amount of energy and the one farthest having maximum energy.
6. There is no change in the energy of electrons as they keeping revolving in the same shell and the atom remains stable.

Hope it helps...

Answer 2

Hey,


Thomson's model of an atom:
1.An atom consists of a sphere of positive charge in which electrons are embedded just like seeds in the watermelon.
2. Total positive charge on the sphere is equal to the total negative charge present on the electrons so that atom as a whole is electrically neutral .
3. It could not explain results of rutherford's scatter experiments.


Rutherford Model of an atom :
1.An atom consists of a small positively charged nucleus in the centre and the electrons are revolving around it.
2. There is very large empty space between the nucleus and electron .
3. All the mass of an atom is mainly concentrated in the nucleus .
4. It could not explain the stability of the atom because the revolving electron will be accelerated towards nucleus .hence, it will lose energy. It's Orbit will become smaller and smaller and ultimately the electron will fall into the nucleus.


Bohr 's model of an atom :
1. An atom consists of a small heavy positively charged nucleus in the centre and the electrons revolve around it in circular path called orbits.
2. In a particular , atom the orbit in which the electrons revolve are the discrete orbits having fixed radii and energy. These discrete orbits are ,therefore ,also called energy levels or shells. The term cell is used to indicate that atom is three dimensions .
circular orbits or energy levels or shells around the nucleus.
3.As long as an electron is revolving in a particular Orbit , it can neither lose energy nor gain energy. Thus, the atom is stable and does not collapse. This state of the atom with lowest energy is called ground state of the atom .
4.Energy is lost or gained by an electron only when it jumps from one orbit to the other.
The energy falls on an electron and it absorbs this energy, it will jump to some outer shell.
The atom is then said to be in the excited state. In the excited state, the atom is not stable. It loses or emits energy and jumps from inner shell to outer shell by absorbing energy whereas energy is emitted when an electron jumps from an outer shell to an inner.

HOPE IT HELPS