\(\pi\) bonding to \(\pi\) anti-bonding orbital Lone pair to \(\pi\) anti-bonding orbital After all, how do you describe something that seems to be both particle and wave, and which can have a wide range of frequencies or wavelengths?Ī visible light photon has a wavelength of 500 nm (nm is short for nanometer, 10 -9 m).\) electron jump No one has yet come up with a better system. While it can be confusing at first, this is how the nomenclature developed historically. So, now when scientists talk about light, they might refer to electromagnetic waves or photons of a given energy, frequency, or wavelength. Though Lewis’s theory was inconsistent with many behaviors of light known through experiments, his name for the particles, photons, was adopted immediately and has stuck to this day. It was not until 21 years later that the chemist Gilbert Lewis published his own theory of particle light (now long abandoned) in which he called these particles of light photons. In this way, we can take an image of the sky and determine the brightness of an astronomical object.Įinstein’s idea of light as discrete packets of energy was published in 1905. In astronomy, we make use of the particle nature of light by using the photoelectric effect to record the number of photons that come from a particular region of the sky. Because of the particle nature of light, we can capture the energy of sunlight. In everyday life, the photoelectric effect explains the working of solar panels, for example. This is because no single light particle has the required minimum energy, and these particles are absorbed only one at a time. However, if the frequency of the light is too low, then no electrons can be liberated, no matter how many of them are present. The higher the intensity of light shining on a metal, the more packets, or particles, the metal absorbs and the more electrons are emitted. Since the energy of a particle of light depends on its frequency, an incoming particle with a high enough frequency will have enough energy to liberate an electron from a metal. More precisely, Einstein showed that light behaves as if it were made of discrete particles when it is absorbed. In deducing how the photoelectric effect works, Einstein showed that light can be modeled as discrete little packets, like particles, each having energy \(hf\). It was Albert Einstein (1879-1955) who clarified the matter when he explained the photoelectric effect. Until this time, models of electromagnetic radiation predicted that the energy of light should depend on its amplitude, or intensity they could not explain the dependence on frequency. The equation means that the higher the frequency of a photon, the higher its energy. In SI units, Planck’s constant is 6.626 × 10 -34 J s. The constant of proportionality, \(h\), is called Planck’s constant. Where the SI units for energy are joules (J) and the units for frequency are Hz. More specifically, the German physicist Max Planck (1858 – 1947) showed that the energy \(E\) of light with frequency \(f\) is given by the expression below. This is known as the photoelectric effect. In subsequent experiments, physicists found that the amount of energy absorbed by the metal depends on the frequency of the light that is shining on it. Toward the end of the 19th century, Heinrich Hertz first observed that when a metal is exposed to light, it will absorb energy from the light and emit electrons. In some cases, light behaves more like particles. There is another way to describe light in addition to electromagnetic waves. ĭo you agree with any of these students and if so, whom?
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