- Person
- Max Born
- Lived
- 1882–1970
- Field
- Quantum mechanics
- From
- German-British
The story
When a metal such as sodium reacts with a halogen such as chlorine, it forms an ionic compound, in this case ordinary table salt. The crystal is held together by the attraction between positive and negative ions, and the energy of that attraction, the lattice energy, is a key to understanding why such compounds form and how stable they are. But it cannot be measured directly.
Max Born had studied crystal lattices since 1912, when he and Theodore von Kármán worked out how atoms vibrate in a solid. During the First World War he was in Berlin, where he formed a lifelong friendship with Albert Einstein. In November 1918, within days of the armistice, a chance meeting with the chemist Fritz Haber led to a discussion of how an ionic compound is formed when a metal reacts with a halogen.
Out of that conversation came the Born–Haber cycle, published in 1919. The chemist Kazimierz Fajans formulated the same approach independently and published it in the same journal, so it is sometimes called the Born–Fajans–Haber cycle.
The cycle breaks the formation of an ionic solid into a series of simple steps: turning the metal into a gas, splitting the halogen molecules into atoms, removing electrons from the metal atoms, adding electrons to the halogen atoms, and finally bringing the gaseous ions together into a crystal. Because of Hess's law, the total energy change is the same whatever path is taken. The overall heat of formation, the sublimation and bond energies, the ionisation energy and the electron affinity can all be measured, so the hard-to-measure lattice energy can be calculated from them.
The method works best for fully ionic solids such as the alkali halides, and an extended version can be used to estimate the polarity of compounds whose bonds are partly covalent.
The cycle linked Born's physics of crystals with practical chemistry. More than a century later it remains a standard part of chemistry courses worldwide, one of the first places students see how energy bookkeeping can reveal what cannot be measured.
Why it matters
Generations of chemistry students have learned how ionic substances hold together through the method Born helped devise.
About Max Born
Physicist who co-founded quantum mechanics and gave the wave function its probability meaning; dismissed from Göttingen by the Nazis in 1933, he won the Nobel Prize in exile in 1954.
More about Max Born
- Max Born founded the physics of vibrating crystalsIn 1912 Max Born and Theodore von Kármán founded lattice dynamics, explaining how atomic vibrations set a solid's properties; Born later wrote the classic text on it.
- Max Born built a home for refugee scientists in EdinburghDriven out of Germany in 1933, Max Born became Tait Professor at Edinburgh in 1936 and built a research group made up mostly of refugees from Europe.
- Max Born trained a generation of great physicistsAt Göttingen in the 1920s Max Born supervised Oppenheimer, Maria Goeppert Mayer, Max Delbrück and others, while Pauli, Heisenberg, Fermi and Wigner served as his assistants.
- Max Born found quantum mechanics' central equationIn 1925 Max Born recognised Heisenberg's new physics as matrix algebra and found its key law, the commutation relation now carved on his gravestone.
- Max Born showed quantum waves give probabilitiesIn 1926 Max Born proposed that the quantum wave function gives the probability of finding a particle, the Born rule, winning a share of the 1954 Nobel Prize.
- Max Born co-wrote the classic book on opticsMax Born and Emil Wolf wrote Principles of Optics, published in 1959, which became a standard reference on the physics of light for generations of scientists.
- Max Born rallied Nobel laureates against nuclear warIn 1955 Max Born and Otto Hahn initiated the Mainau Declaration, in which Nobel laureates warned against nuclear weapons; within a year 52 laureates had signed.
Sources
- Max Born Wikipedia
- Born–Haber cycle Wikipedia
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