Chemical Formulas (Formulae? It’s Geek to Me)

Now that we’ve looked into naming chemicals, we need to look into formulas. There are several types of formula, each providing us with information. At its simplest form (molecular) the formula provides us with the elements comprising the compound and the number of each. Previously we considered two oxides of carbon, one containing equal numbers of carbon and oxygen (CO, carbon monoxide) and (CO2, carbon dioxide). The former depicts a substance containing equal amounts of carbon and oxygen, and the latter where carbon is chemically bonded with 2 atoms of oxygen.

There are several types of chemical formulas. One of the things chemists often need to do is calculate molecular weight. From the simplest formula, we can calculate the sum of the weights of the elements. For instance, consider baking soda, NaHCO3. From the periodic table, we see sodium having an atomic weight of 22.90, hydrogen weighs in at 1.008, and the 3 atoms of oxygen at 47.997, for a total of ……..drum roll:71.905. (There are two numbers for each element: single one without decimals, atomic number, and one with a decimal and several places, atomic weight). Normally, one sums up all the atomic weight numbers, then rounds to one or two decimal places.

This process works OK for simple compounds. As you know, life just ain’t so simple. For example, the sugar glucose has the formula C6H12O6. This tells us how to calculate its molecular weight, but…….this formula is shared by the sugar we call fructose. To distinguish between them, we need to show how the C’s, H’s and O’s are bonded to each other.

What difference does this make? Quite a bit, at times. For instance, the sweetness power (did I coin a phrase here?) is different between them (why else would we care about them, anyhow). Clearly, we need to go greater in depth.

How can we bond a total of 24 atoms to each other ? The C’s are bonded in four directions. Most are bonded to, on one side, an O which in turn is attached to an H. In another direction, the C (usually called the “central atom”) has an H on one side, and O bonded to H on the other. It can be written as -CHOH. Each C is then bonded to the rest of the molecule. Essentially, the difference between glucose and fructose is in what plane the H’s and OH’s are oriented. Told you this isn’t simple. The term of art for two (or more) compounds having the same formula (collection of atoms) is isomer. Fructose and glucose are isomers.

In most general chemistry courses, the topics taught stress inorganic chemicals; the reality is that the overwhelming majority of chemicals are organic. Glucose and fructose are organic chemicals. As I mentioned previously, if the compound contains carbon, it’s probably organic. But not always.

There are several ways to depict formulae on paper. Each provides additional pieces of information which might be needed by practioners. The simplest are molecular (just the atoms present, with the numbers of each, Just the facts, ma’am, to coin a (very old) phrase. We can use these to look at balancing equations.

This is where the fun ends (or, maybe, begins).

By the way, glucose and fructose can combine with each other, lose a molecule of dihydrogen oxide (do I mean water??) and form sucrose. How ’bout that!

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