![]() Quarks are elementary because quarks cannot be broken down any further. Protons and neutrons are also not elementary particles because they are made up of even smaller particles called quarks joined together by other particles called gluons (because they "glue" the quarks together in the atom). Modern physicsĪtoms are not elementary particles, because they are made of subatomic particles like protons and neutrons. Some idea of present-day atomic physics can be found in the links in the table below. Although this model was well understood, modern physics has developed further, and present-day ideas cannot be made easy to understand. Isotopes vary in the number of neutrons present in the nucleus. This experiment was called the Geiger–Marsden experiment or the Gold Foil Experimentīy this stage the main elements of the atom were clear, plus the discovery that atoms of an element may occur in isotopes. Rutherford showed this when he used an alpha radiation source (from helium) to hit the very thin gold sheets, surrounded by a Zinc sulphide lampshade that produced visible light when hit by alpha emissions. In 1910, the New Zealand physicist Ernest Rutherford put forward the idea that the positive charges of the atom were found mostly in its center, in the nucleus, and the electrons ( e-) around it. Lord Ernest Rutherford later named these positively charged particles protons Rutherford's atomic modelĪtomic experiment of Lord Ernest Rutherford In the same time, experiments by Eugene Goldstein in 1886 with cathode discharge tubes allowed him to establish that the positive charges had a mass of 1.6726 * 10 −27 kg and an electrical charge of +1,6 * 10 −19 C. In 1906, Robert Millikan determined that the electrons had a Coulomb (C) charge of -1.6 * 10 −19, something that allowed calculation of its mass as tiny, equal to 9.109 * 10 −31 kg. The negative charges were named electrons ( e-).Īccording to the assumptions established about the atoms neutral charge, Thomson proposed the first atomic model, that was described as a positively-charged sphere in which the electrons were inlaid (with negative charges). Thomson knew that the atoms were electrically neutral, but he established that, for this to occur, an atom should have the same quantity of negative and positive charges. The plum pudding model was suggested as the first atomic model by J.J Thomson where he suggested that the atom was a sea of positive charge that surrounded small negative electrons. ![]() Crookes named the emission ' cathode rays'.Īfter the cathode ray experiments, Sir Joseph John Thomson established that the emitted ray was formed by negative charges, because they were attracted by the positive pole. When creating a vacuum in the tube, a light discharge can be seen that goes from the cathode (negatively-charged electrode) to the anode (positively-charged electrode). In 1850, Sir William Crookes constructed a ' discharge tube', that is a glass tube with the air removed and metallic electrodes at its ends, connected to a high voltage source. Get every answer correct the first time to score 100. ![]() If you guess wrong 3 times on a question, you will receive no points. Your score will decrease with every wrong guess. Schematic representation of the Thomson model. Welcome to another practice quiz Pick the best answer for each question. ![]()
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