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For millennia, scientists have pondered the mystery of life; namely, what goes into making it. According to Genesis, man was created out of clay and the “breath of life”. However, other cultures put forth the notion that all things were composed of particles, a tiny, indivisible entity that could neither be created nor destroyed. This was a largely philosophical notion however and it was not until the emergence of atomic theory and modern chemistry that scientists began to postulate that all matter was composed of tiny units that, when taken in combination, produced the basic building blocks of all things. Molecules, they called them, taken from the Latin “moles”, which translates to “mass” or “barrier”, but used in this context to mean a small unit of mass.
By its classical definition, a molecule is the smallest particle of a substance that retains the chemical and physical properties of the substance and is composed of two or more atoms; a group of like or different atoms held together by chemical forces. It may consist of atoms of a single chemical element, as with oxygen (O2), or of different elements, as with water (H2O). Molecules as components of matter are common in organic substances (and therefore biochemistry) and make up most of the oceans and atmosphere.
Historically, molecular theory and atomic theory are intertwined. The first recorded mention of matter being made up of “discreet units” began in ancient India where practitioners of Jainism espoused the notion that all things were composed of small indivisible elements that combined to form more complex objects. In ancient Greece, philosophers Leucippus and Democritus coined the term “atomos” when referring to the “smallest indivisible parts of matter”, from which we derive the modern term atom. Then in 1661, naturalist Robert Boyle argued in a treatise on chemistry that matter was composed of various combinations of “corpuscules”, rather than earth, air, wind and fire. However, these observations were confined to the field of philosophy.
It was not until the late 18th and early 19th century when Antoine Lavoisier’s law of conservation of mass and Dalton’s law of multiple proportions brought atoms and molecules into the field of hard science. The former proposed that an element was a basic substance that could not be further broken down, the latter proposing that each element consists of atoms of a single, unique type, and that these atoms can join together to form chemical compounds. A further boon came in 1865 when Johann Josef Loschmidt measured the size of the molecules that make up air, thus giving a sense of scale to molecules.
Today, our concept of molecules is being further refined thanks to ongoing research in the fields of quantum physics, organic chemistry and biochemistry.
We’ve also recorded an entire episode of Astronomy Cast all about Molecules in Space. Listen here, Episode 116: Molecules in Space.