For the past three weeks, we have been focusing on the atom and its structure. This month marks the 100th anniversary of Bohr's foundational work on the subject.
However, long before anyone knew what an atom is or what they were made of or how they behaved, chemists were doing chemistry. Or people were doing chemistry.
ndeed, one could make a strong argument that one of the defining characteristics of humanity is that we practice chemistry, be it in the form of cooking or the making of pottery or the synthesis of paints for the walls of caves. Everyone does chemistry every day.
For much of our history, we have not had a coherent explanation of chemical principles. Instead, chemical transformations were wrapped in the cloak of alchemy. Practitioners engaged in the art as magic with little understanding of why reactions occurred or what compounds were made.
It is perhaps because we have been practicing chemistry for so long that there are so many myths and misconceptions about chemistry. For example, the notion that there is something inherently special or mystical about certain compounds or groupings of compounds still exists today.
This belief arises from the notion that there is a distinction between "organic" and "inorganic" substances - between the substances involved in living organisms and the rest of the world. Living or organic organisms were infused with "elan vital" or vital impetus. Non-living organisms lacked this vitality. Inorganic compounds weren't even dead because they had never been alive.
This all changed in the early 1800s when the chemist Friedrich Wohler was able to synthesize urea - a well-recognized and characterized organic compound - from inorganic starting material. Clearly the theory of a vital force was incorrect.
Since Wohler's time, chemist have embarked on a campaign of synthesizing the compounds found in nature such as vitamins, sugars, lipids, fats, and proteins while also exploring the many other compounds that are possible.
For much of the 1800s, synthetic organic chemistry was devoted to isolating and labeling the various compounds found in the natural world. In some case, such as salicylic acid, chemists were able to both isolate and modify the compound. Salicylic acid is found in tree bark and is moderately effective at relieving headaches and body aches.
Acetylated salicylic acid or "Acetylsalicylic acid" was much more effective at treating headaches and body aches. So much so that the generic name "aspirin" is part of our common language.
Many compounds were isolated and characterized as organic chemistry blossomed from simply a study of the chemicals in living things to a major area of research. We have now characterized and synthesized millions of organic compounds ranging from simple hydrocarbons to complex molecules such as hemoglobin and Vitamin B12.
Still, during the 1800s and well into the 1900s, we didn't have a good explanation of chemistry at the atomic and molecular level.
With the development of the quantum mechanical atom, chemists turned their attention to understanding why certain atoms will group together with others. How do four phosphorus atoms bind together to give white phosphorus which is potentially toxic? How do those same four phosphorus atoms react with water to give phosphoric acid which is essential for life?
This duality for many chemicals can be confusing. How can an element have both detrimental and beneficial properties?
Chemistry, of course, isn't just about atoms. If it was, once we had isolated all of the elements, chemistry would have been finished.
No. Chemistry is about how atoms interact with one another. It is about all of the chemical compounds from salicylic acid to hemoglobin, from white phosphorus to Adenosine TriPhosphate or ATP.
Once we understood the quantum mechanical atom, the question of why certain elements clump together to form distinct compounds didn't take many years to understand. The simple answer to the question is "bonding" although that is a bit like saying that a car runs because it burns gasoline. True, but not the whole explanation.
For the most part, bonding can be divided into three categories: Covalent, Ionic, and Metallic. Each type of bonding has its own peculiarities. Each generates different chemical consequences.
For example, fluoride ions in a compound such as sodium fluoride readily dissolved in water to give aqueous ions that are free and independent of the sodium ions. Any ionic compound capable of generating fluoride ions generates exactly the same fluoride ions which have no trace of their origin. This is a consequence of an ionic bond.
On the other hand, fluorine atoms covalently bonded as part of a glucose molecule can never break away on their own. They are stuck in place and will not generate fluoride ions.
This difference is important to chemistry and helps to answer the question of why some compounds are good for you even though they contain elements that might be bad under other circumstances.
More on bonding next week.
