Radioactivity Flashcards
Democritus 500 BC - Atomic theory of
Everything were made from tiny particles (atomos), which were separated from empty space.
John Dalton 1804
Agreed with Democritus that everything was made from tiny particles and described them as solid spheres. He also suggested that each element was made up of a different type of atom
J.J. Thompson - 1897
Plum Pudding model - He said that atoms could not be solid spheres, he discovered electrons (- charged), he said that atoms were a general ball of positive charge with discrete electrons stuck in it
Rutherford + Students - 1909
Alpha particle scattering - alpha particles passed straight through the but some deflected to the sides and some deflected back. Showing mass is concentrated in the centre and the centre is positive with a cloud of electrons, the nuclear model. However there was a flaw because there is nothing to stop the cloud of negative electrons rushing into the positive nucleus, so the atom should automatically collapse
Niels Bohr - 1913
Electrons orbited the nucleus in electron shells. Preventing the atom from collapsing
Rutherford
The positive charge in the nucleus is made up of small discrete particles called protons
James Chadwick
Discovered Neutro particles in the nucleus called neutrons
Development of the model of the atom
500 BC - Democritus
1804 - John Dalton
1897 - J.J. Thompson
1909 - Rutherford + Students
Development of the model of the atom
500 BC - Democritus 1804 - John Dalton 1897 - J.J. Thompson 1909 - Rutherford + Students 1913 - Niels Bohr Rutherford Jamea Chadwick
Alpha particle scattering
Fired positively charged alpha particles into a thin sheet of Gold. The idea was that if the positive charge in the gold atoms were generally spread out ( as J.J Thompson proposed from the plum pudding model) the alpha particles should pass straight through the thin sheet of gold because the weak spread of positive charge would not be strong enough to affect them. However, in the experiment, some of the alpha particles deflected to the side and some even deflected back the way they had come. Proving J.J Thompsons theory wrong. Because most of the particles were deflected back, scientists realised that most of the mass is concentrated at the centre in a tiny nucleus, which has a positive charge as it repelled the alpha particles. They also realised that because nearly all the alpha particles passed straight through, most of an atom is empty space
