History Of The Atom ATOMS, BONDING AND MOLES Flashcards
In the early 1800s what did John Dalton believe about the atom?
He suggested that substances were made up of atoms which were like small and hard spheres. He also suggested that each chemical element has its own atoms that differed from others in terms of their mass.
Who discovered the electron?
At the end of the 1800s a scientist called J.J. Thomson discovered the electron.
How did J.J. Thomson discover the electron?
By applying high voltages to gases at low pressure.
How did Thomson imagine the atom?
Like a plum pudding. He knew electrons were negatively charged because beams of particles were attracted to positive charges.
He knew that atoms themselves carry no charge so decided that they must be embedded in a cloud of positive charges.
How was the nucleus discovered?
The alpha particle scattering experiment.
Who carries out the alpha particle scattering experiment?
Geiger and Marsden.
What happened in the alpha particle scattering experiment?
Some rays were deflected by the gold foil.
This is because the nucleus is positive, therefore, it reflects the positive rays (if it gets hit straight on)
If the nucleus is skinned by the rays, they get decelerated in another direction.
How were electron shells discovered?
Niels Bohr noticed that the light given out when atoms were heated only had specific amounts of energy. Therefore, he decided that electrons must be orbiting the nucleus at set distances, in certain fixed energy levels.
How are the neutrons discovered?
James Chadwick did an experiment which could only be explained by the existence of neutrons. The neutrons must have no charge and have the same mass as a proton.
