ATOMIC STRUCTURE
An atom
has a very complex structure which resembles a miniature solar system. For
simplicity, it may be considered to be a tiny sphere.
An atom of any element consists of the nucleus and the
electrons. The nucleus is a stationary mass, situated at the centre and carrying a
net positive charge. It consists of heavy particles-protons and neutrons. Each
of these particles are 1836 times heavier than an electron. Each proton carries
a positive charge, while the neutron carries no charge.
The electrons revolve around the nucleus in definite orbits. They are
bound to the nucleus by different energy levels. An electron has a very small
mass, and carries a net negative charge. In its normal state an atom carries
equal number of electrons and protons, and is therefore electrically neutral.
Energy levels and quantum numbers:
The electrons in the atom are
arranged in different shells, known as K-shell, L-shell, M-shell, etc. Each
shall includes a fixed number of orbits. These shells are further divided into
subshells depending upon the total number of electrons in each shell. Each
subshell (orbit) is at a definite distance and the nucleus exerts a definite
force on the electrons in this subshell. This force is known as the energy of
the orbit. Each subshell which can be occupied by the electrons is called energy level in the atom. Each electron of
the atom belongs to a particular orbit and hence occupies a definite energy
level. The total energy of the atom is the sum of the energy levels occupied by
the different electrons. The arrangement of electrons in different orbits is
such that it produces a minimum total energy in the atom. This arrangement of
electrons becomes the most stable state of
the atom. If an electron occupies a higher energy orbit, it is called an excited state of the atom.
Various shells, the subshells and the number of
electrons which can occupy a given subshell .
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