The History of Molecular Geometry
Molecular geometry is just one aspect of molecular science. Molecular science can include molecular sizes, formulas, and spectroscopy. The concepts of molecular geometry and molecular science were first conveyed by Amedeo Avogadro in 1811, but it took a hundred years before the science was codified by Jean Perrin. In molecular geometry, the structures of molecules are fixed at certain bond lengths and angles. The overall shape of molecules is important for determining their properties.
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Molecular Science
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Molecular science is a general term that encompasses the science of molecules, particularly molecular chemistry and molecular physics. Although molecular chemistry studies the chemical bonds between molecules and how they form and break, molecular physics focuses more on determining their structure and properties. Molecular geometry is a focus under molecular physics because of the important of structure.
Molecular Geometry
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Molecular geometry is the study of how molecules are arranged. It can show what molecules are attached to one another and then can tell the lengths of the bonds as well as the angles at which the bonds are made. Although the bonds are fixed, so the lengths and angles do not change, molecules do rotate and revolve, making accurate measurements difficult. Molecular geometry is useful for determining reactivity, polarity, magnetism, and other physical properties.
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Dalton and Gay-Lussac
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During the nineteenth century molecular science was a new concept, and scientists such as John Dalton and Joseph Louis Gay-Lussac tried to come up with their own theories to explain molecules and atoms. Dalton had no method to measure atoms and never differentiated atoms from molecules. Gay-Lussac was able to determine the ratios of gases were small numbers but didn't go further in his work.
Avogadro
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Lorenzo Romano Amedeo Carlo Avogadro, conte di Quaregna e di Cerreto, commonly known as Amedeo Avogadro, was an Italian scientist born in Turin, Italy, on 9 August 1776. Avogadro was able to determine that atoms and molecules were not the same thing. Although all things are made of atoms, the number of each atom in the substance was the molecule. For example, water was made of two molecules of hydrogen and one molecule of oxygen.
Perrin
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Jean Perrin began studying Brownian motion in 1908. Brownian motion is the theory of erratic movement of particles in an otherwise immobile liquid. Albert Einstein predicted that water molecules were in random motion but had no hard evidence. Using the new ultramicroscope developed during this time period, Perrin was able to experiment and estimate the sizes of molecules and atoms and their quantity. With reliable experimentation, molecules became more of a solid science and not just a hypothesis.
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References
- Photo Credit Image by Flickr.com, courtesy of Christian Guthier
