List each scientist who contributed to today's understanding of the atom along with his contribution.?

Answer 1

Philosophical atomic ruminations date back to the ancient Greeks and Indians in the fifth and sixth centuries BCE. It was the Greeks (Democritus; see below) who coined the term atomos, which meant "uncuttable".

The first philosophical statements relating to an idea similar to atoms was developed by Democritus in Greece in the fifth century BCE around 450 BCE. The idea was lost for centuries until scientific interest was rekindled during the Renaissance Period.

In 1803, John Dalton used the concept of atoms to explain why elements always reacted in simple proportions, and why certain gases dissolved better in water than others. He proposed that each element consists of atoms of a single, unique type, and that these atoms could join up to form compound chemicals.

In 1897, JJ Thomson, through his work on cathode rays, discovered the electron and their subatomic nature, which destroyed the concept of atoms as being indivisible units. Later, Thomson also discovered the existence of isotopes through his work on ionized gases.

Thomson believed that the electrons were distributed evenly throughout the atom, balanced by the presence of a uniform sea of positive charge. However, in 1909, the gold foil experiment of Ernest Rutherford suggested that the positive charge of an atom and most of its mass was concentrated in a nucleus at the centre of the atom, with the electrons orbiting it like planets around a sun. In 1913, Niels Bohr added quantum mechanics into this model, which now stated that the electrons were confined to clearly defined orbits and could not freely spiral in or out.

In 1926, Erwin Schrodinger, using Louis DeBroglie's 1924 proposal that electrons behave like waves in an atom, wrote out a wave equation for the electrons in an atom, which had solutions describing electron orbitals. A consequence of this notion, pointed out by Werner Heisenberg a year later, is that it is mathematically impossible to obtain precise values for both the position and momentum of a particle at any point in time; this became known as the Uncertainty principle. Instead, for any given value of position you could only obtain a range of probable values for momentum, and vice versa. Thus, the planetary model of the atom was discarded in favor of one that described orbital zones around the nucleus where a given electron is most likely to exist.

Answer 2

niels bohr - the first model of the atom: nucleus+electrons
max planck - energy is not continuus
de Broglie: matter is also a wave, just like light
einstein - relativity theory, duality particle-wave of light