Because in CH4 the valence electrons of Carbon are being pulled away from the nucleus with the same force (since all hydrogen has the same electronegativity).So charges are equally distributed throughout the atom and the atom is non-polar. In CH3Cl Cl has a different electronegativity than H, so charges aren't equally distributed and therefore the molecule is polar.
Yes they are stable because they follow octet rule but am not sure if they are exist separetly
Democritus was the one who had theorized that atoms make up everything and they are indivisible.
Dalton was the creator of the first actual atomic theory, most of his research was on gasses and meteorology.
Thompson was the original man who put together the plum pudding model in which Rutherford later proved wrong during his career.
Rutherford had discovered the nucleus within an atom. He had put together gold foil experiment.
Bohr had developed the idea of neutrons and electrons surrounding the nucleus. He was also the creator of the planetary model we now use to calculate electrons with.
