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Atomic Structure

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The Indian philosopher, Kannad suggested that matter is made up of several small particles
called anu which cannot be broken down further.
Sommerfeld modified Bohr’s model by introducing the idea of motion of electrons in
elliptical orbits.
Schrodinger formulated a new model called quantum mechanical model of atom or wave
mechanical model of atom.
Atoms can be divided into two main parts: the nucleus and the extra-nuclear part.
Electrons, protons and neutrons are identified as fundamental particles. The nucleus of an
atom comprises protons and neutrons, and electrons are present in the extra-nuclear part.
The numbers which designate and distinguish the various atomic orbitals and the electrons
present in them are called quantum numbers. The four quantum numbers are as follows:
Principal quantum number (n)
Azimuthal quantum number (l)
Magnetic quantum number (m)
Spin quantum number (s)
The Principal quantum number determines the energy of the shell.
The Azimuthal quantum number represents the sub-shell to which an electron belongs.
The Magnetic quantum number represents the orientation of an atomic orbital in space.
The Spin quantum number represents the direction of the spin of the electrons.
The distribution of electrons in the different orbitals of an atom of an element is called
electronic configuration.

STRUCTUREE OF ATOM


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ATOMS

ATOMS ARE SMALLEST
ELEMENT OF MATTER .
2. ATOMS ARE MADE UP OF
THREE SUBATOMIC
PARTICLES : ELECTRONS,
PROTONS AND NEUTRONS.
3. PROTON AND NEUTRON ARE
PRESENT IN A SMALL NUCLEUS AT
THE CENTER OF ATOM.
4.ELECTRON ARE PRESENT OUTSIDE THE
NUCLEUS.
5. ATOMS HAVE FOUR SHELL K, L, M, N.

DISCOVERY OF ELECTRON

THE EXISTENCE OF ELECTRON IN AN ATOM WAS SHOWN BY J.J THOMSAN IN 1897.THOMSON PASSED ELECTRICITY AT HIGH VOLTAGE THROUGH A GAS AT VERY LOW PRESSURE TAKEN IN A DISCHARGE TUBE.STREAMS OF MINUTE PARTICLES WERE GIVEN OUT BY CATHODE (NEGATIVE ELECTRODE).THESE STREAMS OF PARTICAL ARE CALLED CATHODE RAYS (BECAUSE THEY COME OUT OF CATHODE). THE MASS AND CHARGE OF THE CATHODE RAY
PARTICLES DOES NOT DEPEND ON THE NATURE OF GAS TAKEN IN THE DISCHARGE TUBE. CATHODE RAYS CONSISTS OF SMALL, NEGATIVELY CHARGED PARTICLES CALLED ELECTRONS. SINCE ALL THE GASES FROM CATHODE RAYS, IT WAS CONCLUDE THAT ALL THE ATOMS CONTAIN NEGATIVELY CHARGED PARTICLES CALLED ELECTRONS.

DISCOVERY OF PROTON

SOMEWHERE BETWEEN THOMSON AND CHADWICK, PHYSICISTS REALIZED THAT THERE ARE POSITIVELY CHARGED CONSTITUENTS OF THE NUCLEUS, WHICH WE CALL 'PROTONS'. THE WAY THIS HAPPENED WAS A GRADUAL PROCESS, AND THAT IS WHY IT IS HARD TO SAY EXACTLY WHO DISCOVERED THE PROTON, ALTHOUGH IF YOU HAD PUT A NAME AGAINST IT, IT WOULD BE RUTHFORD, SORT OF.  AFTER THE DISCOVERY OF THE ELECTRON, IT WAS REALIZED THAT THERE MUST

RATHERFORD’S MODAL OF AN ATOM

BY 1911 THE COMPONENTS OF THE ATOM HAD BEEN DISCOVERED. THE ATOM CONSISTED OF SUBATOMIC PARTICLES CALLED PROTONS AND ELECTRONS. HOWEVER, IT WAS NOT CLEAR HOW THESE PROTONS AND ELECTRONS WERE ARRANGED WITHIN THE ATOM. J.J. THOMSON SUGGESTED THE"PLUM PUDDING" MODEL. IN THIS MODEL THE ELECTRONS AND PROTONS ARE UNIFORMLY MIXED THROUGHOUT THE ATOM: