Atomic Theories: Who and When

[caffinatedloz]

Hey guys! In order to teach myself more about how we came to know so much about atoms and atomic structures, and learn about the early proposed theories and scientific experiments, I thought I'd create this thread and write about a new theory every couple of days, moving in chronological order. I hope that everyone else who is studying 1/2 chemistry will find this thread interesting and useful for your studies.

1802: John Dalton
John Dalton was a chemist, born in 1766 in England. His work included identifying the fact that red-green colour blindness was hereditary and studying the behaviour of atoms in terms of weight. Despite coming from a poor background and not having a high level of education, he went on to become a great scientist with a keen interest in meteorology.

Dalton asserted that all matter (solid, liquid and gas) is made up of tiny spherical individual particles, both indivisible and indestructible. He came up with the name atoms, from the Greek term "atomos" meaning undivided. He also identified the fact that substances containing one type of atom were particular elements while substances with different type of atoms were compounds and believed that elements could not be broken down further.

Many of the beliefs that Dalton had turned out to be true (according to our current understanding), however, there was still a lot more to learn about what made "types" of atoms different and the fact that atoms contained different types of smaller particles.

[angewina_naguen]

Loving this heaps, laura_  What a brilliant thread idea! I haven't touched science in years myself but I know this will benefit so many others who are  Keep up the good work and have a happy new year!

[caffinatedloz]

1913: Niels Bohr
Neils Bohr was a Danish physicist. In his lifetime, he made many contributions to our understanding of science. One of the most significant was the Bohr model for an atom which he proposed.

- The Bohr model suggested that electrons revolved around the nucleus in a fixed and circular manner.
- He believed that the way that electrons orbit corresponded to specific energy levels in the atom.
- He believed that electrons could only occupy one fixed energy level and could not exist between two.
- He believed that electrons orbiting further away from the nucleus had higher energy levels.

He believed that electrons could move between energy levels by absorbing or emitting energy (eg. light), which he backed up by calculating energy looking at the distance between lines on the hydrogen emission spectra. Other scientists quickly built on this as they researched and proposed models for other elements.

Neils Bohr was awarded a Nobel prize for his work. He also founded the Insitute of Theoretical Physics at Copenhagen University in the 1920's. This is now known as the Neils Bohr Institute. The element Bohrium was also named after him (as it was an element that he hypothesised existed).