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Question 1

order of the discovery of the atom as it is today

Answer 1

before the electron was discovered, the atom was said to be tiny spheres that could not be divided
the electron led to the discovery of the PLUM PUDDING model - a ball of positive charge with negative electrons embedded
then the alpha particle scattering experiment disproved the plum pudding model -> most particles went straight through showing it was mainly empty space, some deflected showing there was something dense, and some repelled showing there was something positive. this led to the NUCLEAR model forming
Niels Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances
then protons were discovered
- then james chadwick discovered the existence of the neutron which helped with understanding isotopes

Question 2

history of periodic table

Answer 2

Before the discovery of protons, neutrons and electrons, scientists arranged elements in order of their atomic weights.
- The early periodic tables were incomplete and some elements were placed in inappropriate groups if the strict order of atomic weights was followed.
Mendeleev overcame some of the problems by leaving gaps for elements that he thought had not been discovered and in some places changed the order based on atomic weights.
- Elements with properties predicted by Mendeleev were discovered and filled the gaps.
- Knowledge of isotopes made it possible to explain why the order based on atomic weights was not always
correct.