The Progress of the Atomic structure Different theories about the atomic structure were introduced over time. These theories changed as a result of development of different experiments. Leucippus was the first to introduce the theory of atomism, however he didn’t write about his theories in detail. However, Democritus, his student wrote about the theory of atoms in detail. He theorised that everything was composed of atoms and that atoms are solid and indestructible. He also had a theory that there’s a relation between the solidness of the material and the type of atoms it’s made of as atoms differ in shape, mass and size.
For example: metal is made from solid atoms that interlock with each other mechanically to keep them in place. On the other hand water is composed of slippery smooth atoms that allow the water to have its flexible properties. Robert Doyle was a scientist who built up his theories by conducting experimental observations. He discovered that in solids particles were put in fixed position hence their properties and that unlike solids, liquids and gases are composed of particles that are free to move hence the properties of liquids and gases.
He also discovered that by mixing these tiny particles, compounds are made or as he called them “mixt bodies”. In 1803 John Dalton developed the theory of atomism by conducting different experiments and he found out that each element is composed of different atoms to other elements. He also theorised that all the atoms in an element is identical and that compounds are made of two kinds of atoms combined together, which lead him to develop the idea that chemical reactions change the way atoms are grouped together.
He also had a theory that atoms are in and could not be created nor destroyed and they can’t be divided into smaller sections. Eugen Goldstein was a physicist, who experimented with electrical discharge tube by passing an electric current between an anode and a cathode surrounded by gas at a very low pressure in a sealed tube. He believed that negative particles were produced when gas particles spilt in the tube as the cathode rays contained negatively charged particles. He also discovered that agnetic fields could deflect cathode rays and he detected heavy positive particles. Discovering that atoms with similar atomic weights have similar properties was also a big step in the progress of understanding the atomic structure and it was done by Dmitri Mendeleev. He also discovered that there’s a relation between the magnitude of the atoms and the character of the element. J. J Thomson is another scientist that made significant discoveries about atomism. He discovered electrons by experimenting with cathode rays and he found out that electric fields could deflect rays.
He concluded that these rays were negative particles and he called them “corpuscles”. He also proved Democritus and Dalton wrong by discovering that atoms are divisible as he believed that the corpuscles divided from the atoms of the trace gas in the cathode tube. He used the plum pudding model to explain the overall charge of the atom as he theorised that the corpuscles were implanted in a positive charge and the two opposite charges cancelled each other out. Discovering the basic design of the atom was done by Ernest Rutherford.
Rutherford experimented by shooting alpha particles at a sheet of gold and he found out that some of the particles passed right through, which meant that there’s some empty space between the atoms and that they’re not solid particles that are interlocked with each other. He also found out that some particles shot right back, which meant that they hit the positively charged nucleus and they were repelled as they are positively charged as well. Some atoms were deflected as they were attracted to negatively charged electrons that surround the atoms.
The atomic mass was more than the atomic number and the electrons didn’t contribute to the weight of the atoms, so there had to be other particles. The neutron was an unknown particle in the atom, until James Chadwick used a radio active element to detect particles and he discovered that there were particles that are neutrally charged, the neutrons. This discovery was a great step in developing the theory of atomism as it helped to discover nuclear fission and develop nuclear power. The understanding of the atomic number was weak as scientists believed that the atomic number was just a number that increased the mass of the atom.
However, Henry Moseley proved that there’re strong physical basis and he used it to rearrange the elements in the period table. Marie Curie used the electrometer, a sensitive device that detects and measures electrical charge, to discover that uranium rays caused the air around it to have charge and that that the activity of the uranium compounds depended only on the quantity of uranium present. She also discovered that radiation emits from the atoms themselves which proved the pervious theories about radiation emitting from molecules interacting with each other.
Her experiments included pitchblende and torbernite, another two uranium minerals and the electrometer showed that pitchblende four times as active as uranium. She also discovered that torbernite is twice as active as uranium. However she was unaware of the effects of radioactive which resulted in her death. Neil Bohr is a scientist who discovered that the electrons of the atom roam around the nucleus in orbits. He also discovered that the number of the electrons in the outer shells of the atoms determines the chemical properties of the element and it determines which element it bonds with.
Plus he discovered the isotope in uranium that’s responsible for slow neutron fission. Fredrick Soddy was a scientist who experimented with radioactive materials to discover that radio active material decays and that certain types of radiation can blocked off with certain types of materials. He experimented with radio active radium by putting it inside of a glass envelope and that the alpha particles could pass through the thin glass wall but they were contained inside of the glass wall.
He also found out that the same elements could have different masses but they’ll have the same atomic number. In conclusion, our knowledge about the atomic structure and the properties of the atom progressed overtime as there were more theories and experiments that revolved around it. A lot of these theories might have been proven wrong and they might have hindered progress. In my opinion, I think that Ernest Rutherford’s theories have made the most impact in helping us understand the atomic structure.