Models of atom

Thomson’s model

Model

Atom is a positive charge having electrons embedded in such a way that the net charge of the atom is zero.

 Merits

This model explained the electrical neutral nature of the atom.

Limitations

It could not explain the subsequent experiment done on atoms and conclusions derived from them.

Rutherford’s model

 

Model

 The entire mass of atom is concentrated into center called nucleus.  Electrons move at very high speeds around the nucleus in closed the circular path.

Merits

This model gave the idea of the nucleus.

It could not explain the stability of the and the atomic spectrum of hydrogen.

Bohr’s model

Electrons move around the nucleus in certain specified circular orbits and do not lose energy as long as they move in that particular orbit.

Merits 

The model explained   stability of atom and the atomic spectrum of hydrogen.

Limitation

It could not explain the spectra of atoms containing more than one electron.

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Discovery of nucleus

 

In 1911, Lord Rutherford, a scientist from New Zealand, directed a stream of alpha partials toward a very thin gold foil. He selected a gold foil because he wanted as a thin a layer as possible and gold is the most malleable metal.

He observed that:

 

1.     ➧ Most of the alpha particles passed straight through the foil.

2.      ➧Some alpha particles were slightly deflected from their straight path.

3.    ➧   Very few alpha particles were either deflected by very large angles or   completely bounced back.

   ➧Later, Rutherford generalised these results of alpha particles scattering experiment and suggested a model of the atom that is known as Rutherford Atomic Model.

    An alpha particle is a doubly charged helium ion He²⁺, containing two protons and two   neutrons. It is formed by removing of two electrons from helium atom.

According to this model:

 

1.      The atom contains a large empty space.

2.    There is a positively charged mass at the center of the atoms, known as the nucleus, in which the entire mass of the atoms is concentrated.

3.    The size of the nucleus is very small.

4.     The electrons revolve around the nucleus at large distances from each other and from the nucleus.

5.     An atom as a whole is electrically neutral, because the total positive charge of the nucleus is balanced by the total negatively charge of the electrons.

Rutherford model of atomic structure is similar to structure of the solar system. Just as in the solar system, the sun is as the center having the maximum mass and the planet revolved around it, similarly in an atom the nucleus contains the main mass and the electrons revolve around it and orbit shells.

OZONE

 

Ozone⏩

    ⏩Ozone is a light bluish gas found in the upper layer of atmosphere (stratosphere).

    ⏩Ozone is formed by the action of ultraviolet rays of the sun on oxygen.

                                3O₂(g) à 2O₃(g)

Funtions Of Ozone In Atmosphere

  ⏩The ozone layer acts as a blanket in the atmosphere above 16km from the earth‘s surface.

   ⏩Ozone absorbs the harmful ultraviolet rays coming from the sun and thus prevents them from reaching the earth.

DESTRUCTION OF OZONE LAYER

   ⏩Decrease in quantity of ozone in the atmosphere is called the Depletion of Ozone, which leads to the formation of an ozone hole.

  ⏩Due to the ozone hole, Ultraviolet rays of the Sun reaches the earth and causes diseases like skin cancer.

HARMFUL EFFECTS OF OZONE

    ⏩Ozone is poisonous gas with chlorine like smell.

    ⏩It causes respiratory problems.

    ⏩It damages plants and trees.

    ⏩It causes damage to automobile tyres and asphalt.