(a) What is the g

(a) Substances that are made of two or more materials and which can be separated by physical methods are known as mixtures, such as the mixture of salt and water, the mixture of sugar and water, the mixture of different gases, air, etc. In a mixture, components do not combine chemically or through any chemical change. In a mixture, components do not lose their properties.

(b) Mixture of two or more substances with one phase only, i.e. having no distinct boundary of constituent particles is called a solution. For example, solution of sugar and water, solution of salt and water, lemonade, soft drinks, etc. The solution is a homogeneous mixture of two or more substances; an ordinary mixture is made up of two or more matters and which can be separated by physical methods, such as the mixture of different gases, air. In a mixture, components do not combine chemically or through any chemical change.

OR

In 1911, Rutherford performed the gold foil experiment. He bombarded a stream of a-particles on a gold foil, a thin sheet which was 0.00006 cm thick in an evacuated chamber. An alpha-particle is a positively charged helium ion (He²⁺). A simplified picture of this experiment is shown in the figure.

In this famous experiment, the following observations were made.

● Most of the a-particles passed straight through the foil without any deflection. This concluded that most of the space inside of an atom is empty.

● A few α-particles were deflected through small angles and a few through larger angles. This happened due to the positive charge on alpha-particles and core (nucleus) of the atom. The heavy positively charged ‘core’ was named as the nucleus.

● The number of α-particles that bounced back was very small. This concluded that the volume of the nucleus is very small in comparison to the total volume of the atom.

On the basis of the gold foil experiment, Rutherford concluded that an atom consists of the nucleus which has a positive charge and it is surrounded by electrons that are moving around the nucleus. The number of electrons and protons are equal and the entire mass of the atom is concentrated at its nucleus.

Drawbacks in the Rutherford’s model are:

● According to classical electromagnetic theory, a moving charged particle, such as an electron under the influence of attractive force loses energy continuously in the form of radiations. As a result of this, the electron should lose energy and therefore, should move in even smaller orbits ultimately falling into the nucleus. But the collapse does not occur. There is no explanation for this behaviour