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Size doesn’t always matter. Take a look at the electron- the shrimp of the nucleus, the lightest stable subatomic particle. Despite its small size, it’s absolutely indispensable. Although it’s nearly massless, the electron helps to bind together the atoms that are the stuff of matter. J.J. Thompson discovered the electron in 1897, and since then we’ve been astounded by their weird and wonderful properties. Get ready to learn some truly shocking facts about electrons!
By analyzing questions, you can see patterns emerge, patterns that will help you answer questions. Qwiz5 is all about those patterns. In each installment of Qwiz5, we take an answer line and look at its five most common clues. Here we explore five clues that will help you answer a tossup on electrons.
CATHODE RAYS
Cathode rays made possible the discovery of electrons. Cathode rays were themselves discovered in 1869 by Johann Hittorf. Hittorf was studying the properties of a Crookes tube, a glass bulb containing a partial vacuum with two metal electrodes at either end. When Hittorf applied voltage to the electrodes, he discovered a ray traveling from the cathode to the anode. This ray, while invisible to the naked eye, caused the glass around the anode to glow. Although Hittorf didn’t know it at the time, this invisible beam was a stream of electrons, traveling from the negative cathode to the positive anode.
JJ THOMSON
British physicist JJ Thomson built on Hittorf’s findings. In 1897 he discovered that the cathode rays were streams of negatively-charged particles. Based on these findings, as well as his experiments with positively charged particles in neon gas, Thomson proposed his famous plum pudding model to describe the atom’s structure. According to the plum pudding model, an atom consists of a mass of positively charged particles (the pudding) throughout which electrons are scattered.
ERNEST RUTHERFORD
Thomson’s successors built on his theories and his findings. Ernest Rutherford conducted experiments between 1908-1913 with Geiger and Marsden in which he bombarded gold foil with alpha particles. The scattering pattern of these alpha particles produced findings that led to an adjustment of the plum pudding model. Rutherford proposed that instead of being a positively charged “cloud” an atom contained a small, positively-charged nucleus but was otherwise empty space. It took further experiments to clarify the role of the electrons in this.
ORBITALS
So we know that electrons aren’t located in the positively-charged nucleus. Nor are they floating randomly throughout the atom. Instead, electrons can be found in orbitals around the nucleus. These orbitals aren’t exactly a street address; they’re regions in which the electrons have the greatest probability of being found. Each orbital is assigned its own quantum number. Quantum numbers consist of integers (1, 2, 3, etc.) in conjunction with the letter s, p, d, or f. A law known as the Pauli Exclusion Principle states that no two electrons can have the same set of quantum numbers. Hund’s Rule dictates that each orbital must be filled singly before it will permit a second electron.
OIL-DROP EXPERIMENT
The miniscule size of the electron forced scientists to get creative when analyzing it. In 1909 Robert Millikan and Harvey Fletcher came up with an ingenious way to find the charge of a single electron. The pair’s oil-drop experiment involved suspending charged droplets of oil in mechanical equilibrium between two electrodes. Using known information regarding the mass of the oil droplets and the electric field between the two electrodes, Millikan and Fletcher were able to identify the charge of the electrons.
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Quizbowl is about learning, not rote memorization, so we encourage you to use this as a springboard for further reading rather than as an endpoint. Here are a few things to check out:
To learn more about orbitals and how they determine the properties of different elements, visit this website.
Cathode Ray Tubes are an old invention. Outside of your grandfather’s giant old radio, are they still used today?
Electrons are widely used for an efficient form of mass spectrometry. Learn more about it here!
For a helpful summary of Millikan’s method and set-up, check out this video!
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