In 1896, French scientist Antoine Henri Becquerel discovered radioactivity which was an early contribution to atomic theory. He discovered this phenomenon while experimenting with uranium and a photographic plate.Know More
Becquerel began his experiment by exposing a crystal that contained uranium to sunlight. After the crystal had soaked up some sunshine, Antoine Becquerel placed it on a photographic plate. The uranium crystal imprinted its image on to the photographic plate, leading Becquerel to the conclusion that the uranium was releasing the absorbed energy of the sun in the form of an x-ray. In the absence of light, however, the uranium still imprinted its image on to the photographic plate. Becquerel was surprised, since there was no obvious source of energy involved. He assumed the image was caused by a spontaneous emission from the uranium, but he had in fact discovered radioactivity.
Following up on Becquerel's discovery, Pierre and Marie Curie began experimenting with uranium and the concept of radioactivity. In 1903, the Curies and Becquerel were jointly awarded the Nobel Prize in physics for the discovery of radioactivity and their research. Marie Curie also discovered two new radioactive elements which were named polonium and radium. She was awarded a second Nobel Prize in 1911 for her findings, become the first person to ever be awarded two Nobel Prizes.Learn More
The atomic theory is that all matter is made up of tiny units or particles called atoms. This theory describes the characteristics, structure and behavior of atoms as well as the components that make up atoms. Furthermore, the theory states that all elements are made up of identical atoms.Full Answer >
Bohr's atomic theory suggests that atoms have a positively charged nucleus that is orbited by electrons that move in circles. These electrons move in specific, distinct orbital levels. This theory has since been made obsolete but has had a lasting impact on the understanding of atomic structure and quantum physics.Full Answer >
Dmitri Mendeleev published his periodic table of elements in 1869. His table arranged the known elements according to their chemical properties and in order of their relative atomic mass. This created several gaps in the periodic table and allowed him to predict eight other undiscovered elements correctly.Full Answer >
Antoine Henri Becquerel was a French physicist who, while using newly discovered X-ray technology to study the effects of light on uranium salts, discovered a new type of radiation. This new form of radiation coming from the uranium salts registered on a photographic plate.Full Answer >