Frankland's valence theory Science

Laying the seeds of structural chemistry

On May 10, 1852, Edward Frankland read a paper on organic metallic compounds to the Royal Society in which he made an empirical observation about the theory of valence. Wondering what that is? Let’s find out...  

The celluloid that Rev. Hannibal Goodwin used to make his camera film is a compound created from nitrocellulose and camphor. While nitrocellulose is formed by nitrating cellulose, an organic compound, camphor belongs to the class of compounds called terpenoids, which are large naturally occurring organic chemicals.

The branch of chemistry dealing with organic compounds came from Friedrich August Kekule’s realisation that carbon can form chains and links. This proposal from Kekule in the 1860s was triggered by Edward Frankland, who had stated his theory of valence only in the previous decade.

Troubled childhood

Frankland’s childhood was troubled. As the illegitimate son of Peggy Frankland, he had access to education, but they were treated as outcasts. At 14, Frankland was apprenticed to a pharmacist, Stephen Ross. The five years that followed, from 1840 to 1845, were drudgery, as Frankland worked 70-hour weeks with little learning from Ross.

Still, his interest and talents weren’t quashed. Thanks to local doctors Christopher and James Johnson, Frankland received training in experimental chemistry in the few free hours that he had. He went on to have training stints with reputed chemists including A. W. H. Kolbe, Robert Bunsen and Justus Liebig, completing his doctorate by 1850.

He began working in professorial posts and continued working with organometallics, a class of compounds he had started studying while with Bunsen. Frankland’s observations led him to the theory that when elements combine, they do so in fixed whole number ratios. He called this atomicity, now known in chemistry as valence, and further built on the idea.

On May 10, 1852, Frankland presented his ideas to those gathered at the Royal Society. He stated that elements have fixed combining capabilities, or “only room, so as to speak, for the attachment of a fixed and definite number of the atoms of other elements”. He used the term atomicity, but by the mid 1860s, the expression “valence” or “valency” superseded it.

Kekule built on Frankland’s theory of valency and decided that carbon’s valency must be four. This allowed him postulate the radical idea that carbon can form chains and links. Thus, while Frankland’s theory laid the foundations for modern structural chemistry, Kekule used the same to give rise to organic chemistry.

His other works

As for Frankland, he was involved in numerous other works as well. He helped discover just how exactly muscles consume the energy in food. He worked as a water quality consultant, tirelessly pursuing polluters to ensure clean water and prevent the outbreak of diseases. The fact that he was born out of an affair meant that he didn’t receive a lot of credit that was due to him during his time. Now, of course, we know...


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Printable version | Oct 27, 2021 4:21:23 PM | https://www.thehindu.com/in-school/sh-science/laying-the-seeds-of-structural-chemistry/article8575530.ece

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