ATOM

 

To Be Discussed -

Atomic Physics

Atomic models

1. Dalton
2. J.J Thomson
3. Rutherford
4. Bohr
5. Discovery of Neutron

Atomic Physics - Branch of Physics deals with the structure and characteristics of an atom and subatomic particles.

Models of the Atom

•         Nowadays, we know that atoms are the composition of a positively charged nucleus in the center surrounded by negatively charged electrons.
•         Many attempts were made to develop atomic models to explain the structure and properties of an atom.
•         Now, we are going to discuss how our modern understanding of the atom has evolved over time.

Who gives the idea of an atom

•         The idea of atom was invented by two Greek philosophers, Democritus, and Leucippus in the fifth century BC.
•         The Greek word ατομον (atom) means indivisible.

                                    

•         They believed that atom could not be broken into smaller pieces.

Dalton's model of an atom

•         In  1803, Dalton's atomic model sets up the building blocks for others to improve on.
•         Though some of his conclusions were incorrect, his contributions were vital. His explanation was extra-ordinary for that period of time.
•         Dalton proposed that all matters are composed of atoms
•         When Dalton proposed his model electron and nucleus were unknown. 

JJ Thomson's model of an atom

•         JJ Thomson, who discovered the electron in 1897, proposed the plum pudding model of the atom in 1904.
•         However the atomic nucleus had not been discovered yet.
•         In this model, the atom is made up of negative electrons that float in a soup of positive charge, much like plums in a pudding.

•         In 1906, Thomson awarded the Nobel prize for his work in this field
•         There was still no understanding of how these electrons in the atom were arranged.

Rutherford's model of an atom

•         In 1911, Rutherford tested Thomson's hypothesis by devising his gold foil experiment.

•         His model described the atom as tiny, dense, positively charged core called nucleus surrounded by lighter, negatively charged electrons

Limitations of the Rutherford model

•         An electron accelerating around the nucleus would continuously emit EM radiation and lose energy.
•         It would eventually fall into the nucleus and the atom would collapse.
•         However, this is not consistent with real-world observations- Atoms are stable.

Bohr's model of an atom

•         Proposed in 1913
•         Revised Rutherford's atom to create a more stable model of the atom.
•         Atoms are mostly empty space with a positively charged nucleus surrounded by electrons that travel in circular orbits (like solar system).

Discovery of Neutron

•         In 1920, Rutherford predicted that another kind of particle must present in the nucleus along with the proton.
•         Because if there were only +ve charged protons in the nucleus, then it should break into bits because of the repulsive forces between like-charged protons.
•         To stays atom electrically neutral, this particle would have to be neutral itself.
•         In 1932, James Chadwick discovered the neutron.

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