A Brief History of Periodic Power

By Jonathan Lam on 12/21/15

Tagged: the-homework-life the-homework-life-informative

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You might know this information already, but I'm just writing to write (and teach, if you didn't already know this). We're delving into this subject in class, and I thought I'd write some about it.

The Periodic Table is a wonderful tool — some say it is the most important chemist's tool — that can fit onto a single sheet of paper.

It has the power to predict, to confirm, to contain all the known substances of the world — a remarkable feat for a simple chart.

But how does it work? Who came up with it? For thousands of years, the only known "elements" were fire, wind, earth, and water. In 1790, Lavoisier compiled the 23 known elements. In the early 1800s, with the Industrial Revolution and the discovery of electricity (which could be used to separate compounds into elements), many more elements were discovered. Dobreiner noticed groups of three elements with similar properties, which he called the "model of triads." Newlands then tried to assemble the first periodic table, arranging them by atomic mass. He discovered a pattern, a periodic pattern, in which every seven elements had similar properties. He called this the "law of octaves". The international scientific community frowned up his then-ridiculous ideas and the unscientific association with "octaves," however.

Mendeleev and Meyer also noticed the periodic pattern when organizing the elements and arranged their own tables of the elements simultaneously. They thus created the "periodic law": that the chemical and physical properties of the elements recur when they are arranged by atomic mass. However, Mendeleev is often credited to be the "father of the modern periodic table" because posted his ideas earlier, and was so confident in his predictions — he even predicted the properties of the elements scandium (Sc), gallium (Ga), and germanium (Ge)!

However, as time went on and some some elements did not seem to fit the pattern of atomic mass, Mosely discovered that every element has a unique atomic number (number of protons), and he rewrote the periodic law and reorganized the periodic table by atomic number instead of mass, which fixed the few inconsistencies in Mendeleev's table.

A quick word about the reasons behind periodic law: The periodic table is grouped into columns called groups or families, which have similar properties. The rows are called series, or periods, which have periodic (repeating) patterns of properties. Elements all have a valence shell of electrons, a set of electrons that are the farthest away from the nucleus and have the ability to with other elements. The number of valence electrons determines an atom's chemical and physical properties; and, because of the octet rule — which states that atoms all try to gain, lose, or share electrons to reach a full valence shell — atoms all try to achieve stability in the same way if they have the same number of valence electrons. For example, all alkali metals (family one) are extremely reactive and "want" to rid their single valence electron; similarly, the halogens (family 17) want to gain one more electron to fill their outermost electrons. In addition to the octet rule, other factors also govern other characteristics of atoms such as coulombic attraction, creating trends in atomic properties such as electronegativity, ionization energy, and atomic radius.

There's a lot more to the periodic table, a lot more information lying behind the rules of periodic law that can predict so much about every element, known or unknown.

I'll probably follow up on this soon with any future insight. But that's it for now!