Collect information regarding periodical development of fundamental
particles and structure of atom with different atomic models and displa
then information Chart.
Answers
Answer:
you collect brief information about periodically table on topper app
Collect information regarding periodical development of fundamental
particles and structure of atom with different atomic models and displa
then information Chart.
Explanation:
Discovery of electron, Proton and Neutron
Discovery of electron
It was discovered by J.J Thomson in year 1897.He took Crooke's tube and arranged apparatus as shown in figure:
Observations
• When he passed electric current (at high voltage approximately at 10,000volts) through a gas at pressure 1 atm, then nothing happened as no changes were seen.
• When he reduced the pressure to 10⁻² atm, the whole tube started glowing green .
• He further reduced the pressure to 10⁻⁴ atm, the whole tube stopped glowing, but the faint green was still seen at anode end.
• To confirm, a fluorescent screen was placed at the back of anode and anode was made perforated .When the current was passed through it (at same physical conditions), the Zinc Sulphide screen started glowing which confirmed the following fact.
Conclusion
It proved that at these conditions some rays were emitted through cathode and were travelling towards anode called cathode rays consisting of negatively charged particles. These particles were later called as electron. This is how the electron was discovered.
Discovery of Proton
It was discovered by E.Goldstein in year 1920 .It was actually discovered while carrying out experiment to produce cathode rays .The apparatus used is same .
It was seen when cathode rays were produced (at high voltage and low pressure) they traveled through gas in discharge tube .While doing so, they ionized the gas.
That is, they took electrons of gas along, leaving behind positively charged particles of gas. These particles formed canal rays and started moving towards the cathode .These particles are called canal rays as they are not produced by anode .As these particles possess positive charge so, was named as proton.
Now after knowing about the atom, different attempts were made to know about its structure.
Thomson model of an atom (plum pudding model)
His full name was J.J Thomson and he was the one who made first attempt to explain the structure of atom.
According to him, atom is positively charged sphere in which negative charges are present at certain places like plums in pudding or cherries in ice-cream .But this model was rejected as he could not explain the major point seen in his model.
Drawback: He could not explain the distribution of charges and stability of an atom. As we all know opposite charges attract each other so, how come it is possible that few negative charges remain scattered in this big positive space .They would have been neutralized .So, this could not be explain by J.J Thomson that lead to failure of his attempt.
Rutherford Conclusions of his experiment
• Most of the space in atom is empty
• There is something in centre of an atom called nucleus
• Nucleus is positively charged.
So, According To Rutherford structure of an atom it is similar to solar system.
He said:
- Atom is electrically neutral
- Nucleus is in centre in which protons are present.
- Outside nucleus electrons revolve like planets revolve around sun.
In this model also few limitations were seen and some questions left unanswered which lead to its failure.
Discovery of neutron
It was discovered by Chadwick in year 1932 .It was actually discovered while considering the mass of atomic particles .It was seen that the whole mass of an atom is due to nucleus and as far we know , nucleus is positively charged . That means it has only protons. But we also know that mass of an atom is never equal to number of protons.
This shows, that nucleus contain some other particles also that contribute towards mass not charge .Therefore, the particles were called as neutron (as they possess no charge).
Bohr’s theory
To overcome the limitations of Rutherford model the new concept and picture of atom was given by Neil Bohr which made a great contribution in knowing the structure of an atom.
According to it:
• Atom is electrically neutral i.e. number of Protons = number of Electrons
• In centre of an atom, nucleus is present which is positively charged.
• In nucleus proton and neutrons are present.
Proton possess = +ve
Neutron possess = no charge.
• Outside nucleus, shells or energy levels designated as K,L,M,N ----so on are present.
• In shells electrons revolve
• Electrons possess = -vely charged.
• Each shell has fixed amount of energy .So, as long as electron remain in the same shell it never loses or gain energy when it is in its shell.
• Number of electron in each shell is determined by Bohr Bury rule i.e. 2n².
