Atoms are the building blocks of elements. They are the smallest part of an element that react chemically
Atoms are divisible into still smaller particles called sub-atomic particles. They are electron, proton and the neutron.
Thomsons plumb-pudding model was discarded and Rutherford's model came into being. His model did not stand the test of time as it was having a flaw. According to his theory any revolving electron in circular orbit will radiate energy and finally collapse into the nucleus. Such a situation did not exist. Hence his theory was modified by Boh'r.
Bohr's model was able to explain the spectra of hydrogen.
Bohr postulated that electron moves around the nucleus in circular orbits. Only certain orbits can exist and each orbit correspond to a specific energy.
As an orbit is a clearly defined path and this path can be defined only if we know the exact position and velocity of an electron simultaneously
Boh'r model of the hydrogen atom not only ignores the dual behaviour of electron but also contradicts Heisenberg's uncertainity principle.
Schrodinger proposed an equation incorporating de Broglie concept of wave -particle duality and which is in conformity with Heisenbergs uncertainity principle.
Solution to Schrondinger equation gave us the quantum numbers
The quantum numbers are, principal (n) azimuthal (l) magnetic (ml) and spin (ms)
Electron distribution of an atom containing a number of electrons is divided into shells.
Shells are thought to be divided into sub-shells
If two orbitals have the same n+l values the orbital with the lower value of 'n' has the lower energy .
According to Pauli exclusion principle; no two electrons in an atom can have the same set of four quantum numbers
Hund's rule states that pairing of electrons take place only after vacant orbitals are filled with at least one electron.
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