![]() ![]() ![]() Only when almost all the air has been removed to create a high vacuum – a state that would shatter ordinary glass vessels – can the rays travel the full length of the tube without bumping into air molecules. The quality of Everett’s glassblowing was absolutely crucial for the experiments to work.Ĭathode-rays are produced when an electric current is passed through a vacuum tube. Everett made all of Thomson’s apparatus, and was responsible for operating it – in fact, he generally forbade Thomson from touching anything delicate on the grounds that he was “exceptionally helpless with his hands”. Cambridge’s Cavendish Laboratory, where Thomson spent his scientific career, also has an original tube in its collection.Įach tube was custom-made by Thomson’s talented assistant, Ebenezer Everett, a self-taught glassblower. Using more than one cathode-ray tube in 1897 for his experiments, Thomson managed to identify a particle 1,000 times smaller than the then known smallest piece of matter: a hydrogen atom. I had read lots about Thomson’s famous experiments on the electron – the first subatomic particle to be discovered – but to actually see and touch his apparatus myself, to notice the blackened glass and the tube’s minute features that are omitted in books, brought the object to life. Holding the delicate glass cathode-ray tube in my hands, once used by the great physicist JJ Thomson, was an incredible treat, and an experience I will never forget. Rupert Cole celebrates JJ Thomson’s birthday with a look at one of the star objects in our Collider exhibition. The densely-packed center of the atom is called the nucleus and represents 99.99% of an atom's mass.Rupert Cole celebrates JJ Thomson's birthday with a look at one of the star objects in our Collider exhibition. ➞ reflected particles had a "direct hit" with the center. ➞ deflected particles are those that had come "close to" the positively-charged center. ➞ most alpha-particles pass directly through because the atom is mostly open space. Rutherford's experiments involved bombarding various atoms of gold foil with low-energy alpha particles (α-particles): = Rutherford's Gold Foil Experimentġ911 - Ernest Rutherford disproved Thomson's "Plum Pudding Model" of the atom and discovered the nucleus. ➞ The mass of an electron: m e = 9.1 x 10 -31 kg ➞ The charge of an electron: 1.6 x 10 -19 C = The Charge and Mass of the Electronġ909 - Robert Millikan performed experiments that determined the charge of an electron and the mass of an electron. NOTE - We are not mentioning the word "protons" here. ➞ tiny, negative, point-charges ( raisins) arranged in a spherical cloud ( pudding) of positive charge. In his Plum Pudding Model, Thomson assumes the electrons are spread out like raisins in a pudding: Thomson's Cathode Ray Tube Experiments inspired him to propose his "Plum Pudding Model" of the Atom. Because atoms were known to be neutral, Thomson reasoned that there must be a positive charge somewhere in the atom as well. Because the "cathode rays" were deflected away from the negative end of an applied electric field, Thomson postulated that the cathode rays are negatively-charged particles called electrons.Ģ. When an outside electric field is applied (image on the right), we can see that the electrons (cathode rays) are attracted to the positive end of the applied electric field.ġ. These cathode rays are produced by the applied voltage between the two electrodes. ![]() Thomson's Cathode Ray TubeĪs you can see in the image below, cathode rays are streams of electrons running through the cathode ray tube from cathode to anode. ![]() Thomson as he conducted experiments with a cathode ray tube. The Electron = discovered in 1903 by J.J. 3 - Chemical Quantities and StoichiometryĤ - Types of Chemical Reactions and Solution Stoichiometryħ - Quantum Mechanical View of the Atom, and Periodicityĩ - Covalent Bonding and Molecular Orbitalsġ0 - Liquids, Solids, and Intermolecular Forcesġ5 - Applications of Acid-Base Equilibriaġ6 - Spontaneity, Entropy, and Free Energyġ8 - Transition Metals and Coordination ChemistryĢ0 - An Introduction to Organic Chemistryġ - Structural, Bonding, Molecular PropertiesĢ - The Nature of Organic Compounds: Alkanes and Cycloalkanesģ - Stereochemistry of Alkanes and Cycloalkanes: 3-D Structures of MoleculesĤ - The Study of Organic Reactions: An Overviewġ0 - Substitution (SN2, SN1) and Elimination (E2, E1) Reactionsġ1 - Mass Spectrometry and IR Spectroscopyġ3 - Conjugated Systems and UV Spectroscopyġ5 - Electrophilic Aromatic Substitution (E.A.S.)ġ8 - Aldehydes and Ketones: Nucleophilic Addition ReactionsĢ0 - Carboxylic Acid Derivatives and Nucleophilic Acyl Substitution ReactionsĢ1 - Carbonyl Alpha-Substitution Reactions ![]()
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