TEST YOURSELF 2.2 Chemistry 9th Chapter 2

TEST YOURSELF 2.2

 (1) How was it proved that the whole mass of an atom is located at its centre?

Ans . Since most of the alpha particles in Rutherford's experiment passed through the foil undeflected, therefore most of the volume occupied by an atom is empty. The complete rebounce of a few particles show that the nucleus is very dense and hard.

These observations show that the whole mass of an atom is located at its centre.

 (2) How was it shown that atomic nuclei are positively charged?

Ans . Rutherford bombarded alpha particles on gold foil. These are actually helium nuclei (Ho). The deflection of a few alpha particles proved that there is a 'center of positive

charges in an atom, which is called nucleus of an atom.

(3) Name the particles which determine the mass of an atom?

Ans . The mass of an atom is due to the particles present in the nucleus of an atom. These particles are protons and neutrons.

(4) What is the classical theory of radiation? How does it differ from quantum theory?

Ans . According to Classical Theory of radiation, moving charged particles i.e. electron in an atom release or emit energy continuously. According to Quantum Theory of Max Planck revolving electron in an atom does not absorb or emit energy continuously. The energy of a revolving electron is quantized as it revolves only in orbits of fixed energy.

(5) How can you prove that angular momentum is quantized?

Ans .Let angular momentum (mvr) of 1st orbit is mvr = nh/2TT

By putting the values of h and TT

mvr = 6.63 x 10^-34/2x3.14 = 1.0x 10^-34 kg m²s^-2