Theory of Valence Pioneer: Edward Frankland

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Sir Edward Frankland was one of the foremost English chemists of his day. He laid the foundation of modern structural chemistry through his discovery of the theory of valence, which states that atoms come together to make chemical compounds in regular ratios.

He also introduced the term “bond” to describe the way that atoms link to each other. Frankland became professor of chemistry at the prestigious Royal College of Chemistry and he published Water Analysis for Sanitary Purposes.

Edward Frankland was born in Lancashire, England on January 18, 1825, an illegitimate son of a prominent lawyer. At age 15, he became an apprentice in a chemist’s shop. By 1847, he was a chemistry teacher at Queenwood College, Hampshire, but soon went to Germany in Marburg to work with Robert Bunsen for three months.

Frankland Discovers Organometallic Compounds

While working with Bunsen, Frankland became fascinated by a class of chemicals that bound metal atoms to other compounds, now called organometals. The particular set of these that he was looking at were zinc dialkyls.

An addition to studying organometals, he used these compounds for entertainment. He described the process of adding water to these compounds, which resulted in a greenish blue flame, several feet long, shooting out of the tube. The display caused excitement among those present and it diffused an abominable odor.

This pattern, however, had actually been seen before. A few years earlier, Alexander Crum Brown reported it in his M.D. thesis at the University of Edinburgh, entitled “On the Theory of Chemical Combination.”

A General Symmetry of Chemical Compounds Formula

What both Crum Brown and Frankland saw was that when elements combine, they did so in whole number ratios. Antoine Lavoisier had been moving to the idea when he split and recombined water, and found constant proportions of hydrogen and oxygen were always involved. Frankland took this further and developed what he called atomicity, now known in the chemistry as valence. In his first report he said, “The combining power of the attracting element… is always satisfied by the same number of atoms…”

Frankland’s Valence Theory

The theory of valence states the following:

The valence number equals the number of chemical bonds that any given atom can make with other atoms when forming a compound.

In terms of atomic bonding, the idea is that every atom has a fixed number of bonds that it can form, and that to be stable, all of these bonds must be used. For example, if a hydrogen atom bonds with another hydrogen atom, then the bonds on each atom will be fully used in forming H2, otherwise known as the molecule of hydrogen. Alternatively, two hydrogen atoms can combine with the two bonds of oxygen to form H-0-H, or water. Frankland further introduced the compound notation for what is now known as H20 (water.)

Valence of Carbon Forming Organic Chemical Compounds

Benzene image by Benjah-bmm27

The concept of valence was picked up and developed later by Friedrich August Kerkule, who decided that the valence of carbon must be four. He further suggested a radical idea that this would allow carbon to form into chains of atoms, therefore creating huge molecules. He was right.

In 1865, Kerkule proposed that carbon not only form chains but also link into closed six-atom rings. In the simplest carbon molecule, three of each carbon’s bond on each carbon binds to a hydrogen atom. The resulting molecule is sweet smelling benzene, an organic chemical compound, containing six atoms of carbon and six hydrogen atoms.

Scientific Legacy of Edward Frankland

Edward Frankland’s concept of the theory of valence forms the foundation of modern structural chemistry. Kerkule’s later realization that carbon can form chains and rings gave rise to organic chemistry. Between them, Frankland and Kerkule enabled chemistry to become an important tool in the creation of new complex compound molecules beyond what already existed in their day.

The discovery of the theory of valences produced a huge impact in chemical engineering and industrial purposes that range from medical drugs to textile dyes. For instance, benzene has been used as an additive in gasoline. It has also been used as a solvent and precursor to industrial chemicals in drugs, plastics, dyes and synthetic rubber. Sir Edward Frankland was knighted in 1897. After a brief illness, he died two years later, in August 9, 1899.

Sources:

Farndon, John, etal. The Great Scientists. London: Arcturus Publishing. (2005)

McGovern, Una, Ed. Biographical Dictionary. Edinburgh: Chambers. (2002)

Moore, Pete. E=MC². London: Quintet Publishing Ltd. (2002)

Originally published at Suite101.

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