it was the Greek philosophers who first proposed that matter is made a book particles at a mass means indivisible this is what the term atom was derived from note dates do not need to be learnt off they may however be useful for a science quiz many years later John Dalton an English chemist put forward his famous theory on atomic structure he stated that all matter is made up of tiny particles called atoms and that these atoms are indivisible this means they cannot be broken down into simpler particles William Crookes almost 70 years later performed experiments bypassing electric currents through glass tubes the tubes were maintained under low pressure to help ensure and vacuum was present he did not want molecules in air interfering with his results crooks first experiments involved a maltese cross inside some glass tubing at a glass tubing was attached to a battery and one switch done beams of lights from the cathode was produced the result was a shadow of the Maltese Cross being produced crooks tank included the deed phrase cathode rays travel in straight lines and produce a fluorescence or eleven certificates he could be asked to draw a diagram you crooks the second experiment involved to pad the wheel the setup was largely the same except for a paddle wheel replacing the Maltese Cross the result cathode rays strike the paddle wheel pushing it towards the anode direction crooks concluded that cathode rays must contain particles with enough energy to move the paddle wheel crooks didn't realize us but this was the beginning to discovering electron you not long laser JT Thompson expanded on crooks experiments he wanted to know if the particles had a charge his experiment was similar to crooks however he attached two plates in the vacuum tube when he passed the cathode rays in between uncharged plates they hit the fluorescent screen undeflected however when he charged the plates would use electricity and repeated experiment he found that the cathode rays were deflected towards the positive place he concluded that cathode rays were negatively charged as like charges repel lake charges you Thompson is credited with electron discovery you constant continued to studies on electrons using electromagnets he adjusted the strengths of electromagnets and found a charge to mass ratio of the electron it is very important that you state an exam at Thompson found a charge to mass ratio as he did not discover the mass of electron nor the cherish of electron Thompson made two discoveries he discovered that cathode rays had a negative charge and he discovered the charge to mass ratio of an electron it was Robert Millikan who actually determined to charge on electron his experiment is known as Milliken's oil-drop experiment in 1909 Robert Millikan working at the University of Chicago succeeded in measuring the charge on the electron he allowed a fine spray of oil to settle through a hole into a chamber where he could observe their fall the top and bottom of the chamber consisted of electrically charged plates he introduced a source of x-rays which can cause creation of charges when they strike matter charges produced by the x-rays attached to an oil droplet producing one or more charges on the droplet when there is no voltage applied the fall of the droplets is determined by their mass and the viscosity of air through which they fall when a voltage is applied the droplets that have a negative charge will fall more slowly stop falling or even rise depending on the number of charges on them by adjusting the applied voltage and observing the droplets both with voltage off and voltage on Milligan was able to determine that the charges on the droplets were all multiples of a smallest value one point six times ten to the minus nineteen coulombs he took this to be the charge on a single electron Thompson proposed a straw of NASA in 1898 which is known as Thompson's plum-pudding you are expected to be able to draw and label his diagram although protons had not yet been discovered Thompson new data must be some attractive force to prevent electrons being last all the time his model was widely accepted until 1909 Ernest Rutherford his Larry creditors would provide in the correct structure of an atom Waterford from Bart is a thin piece of gold foil with alpha particles alpha particles are past research particles he made three observations firstly the vast majority of alpha particles went straight through on deflected ly secondly storm alpha particles were deflected at large angles and more surprisingly evolved a tiny amount of health particles were deflected straight back his tree observations led him to make tree conclusions which are discussed in the next slide you are expected to know three observations and Rutherford's tree conclusions from these observations Rochefort stated that the positive particles in the center of the atom are called protons Raja Ford's experiment meant at Thompson's plum pudding model was incorrect as no reflection of alpha particles should have occurred for it model James Chadwick a student of Waterford is credited with the discovery of the neutron the neutron was last to be discovered because I had no charge therefore it was the most difficult to detect Chadwicks performed a very similar experiment to Rutherford except he used beryllium instead of gold behind beryllium was a paraffin wax block the alpha particles knocked neutrons out Tiberium which then caused the neutrons to knock protons Algie paraffin block you need to know the charges and locations of the subatomic particles you also need to know the relative masses you