Naming Molecules Trivia Quiz

The images used in this quiz are called ball-and-stick models of molecules. Each ball represents a single atom - and they are color-coded to help you identify the different kinds of atom. Carbon is black, and hydrogen is white, so this molecule has one carbon atom and four hydrogen atoms, which is written CH4. (Actually, the numbers in all of the formulas should be written below the line of the letters that stand for the elements, but that can't be shown here.)

Carbon is present in so many of the molecules associated with living things that the study of carbon compounds is called organic chemistry. This is the smallest molecule in the group of chemicals called hydrocarbons, which means they are made up of carbon and hydrogen, in varying amounts. Its name starts with meth-, which shows that there is only one carbon atom in the molecule. The -ane ending shows that it has as many hydrogen atoms attached as is possible, which is four, since every carbon atom can be joined to up to four other atoms.

Methane is the main chemical found in natural gas, which is widely used as a fuel for cooking and heating.

As the image shows, this molecule has two carbon atoms, so its name is given the prefix eth-. Once again each carbon atom is joined to four separate other atoms, so its name has the suffix -ane. It is the second member of the alkane family, in which all carbon atoms are joined to each other by a single pair of shared electrons, showed by the black stick connecting the two carbon atoms.

Ethane is a gas under normal circumstances, but not one you will encounter very often. It is most important for its use in industry, to make other more useful chemicals.

Like ethane, ethene has two carbon atoms, but this molecular model shows that there are two sticks connecting them. This is called a double bond, and its presence is indicated by the ending -ene for the name. Because each carbon atom has used two of its four bonding electrons to join the other carbon atom, there is only room for two hydrogen atoms on each of them.

This is the smallest molecule of the alkene family, all of which have at least one double bond between carbon atoms. If there are more than two carbon atoms, the full name will include some numbers to show which ones are connected by a double bond. Double bonds are less stable than single bonds, so these chemicals tend to react easily, replacing the double bond with two single bonds to other atoms. This is called an addition reaction, because new atoms are added onto the molecule, and alkenes are said to be unsaturated, which means they can add more atoms.

Ethene's common name is ethylene. It is used in a number of chemical industries to manufacture new chemicals. One of the most familiar would be the plastic called polythene or polyethylene, in which a bunch of ethene molecules join together to make a long chain, or polymer. It is used for plastic bags, plastic bottles, plastic wrap around fresh foods, and more.

Once again, this molecule has two carbon atoms, and its name starts with eth-. This time, however, the two carbon atoms are sharing three pairs of electrons, shown by the three sticks you can make out in the diagram if you look closely. This is called a triple bond, and is indicated by the ending -yne on the name. Triple bonds are even less stable that double bonds, so these molecules are very reactive, and are not found in nature. They can be produced by processing natural gas.

Ethyne is more commonly called by its old name, acetylene. (The prefix acet- used to be used for substances containing two carbon atoms. It comes from the Latin word for vinegar, where the earliest molecules with two carbon atoms were found.) For many years, a mixture of oxygen and ethyne was used in welding metals, using a device called an oxyacetylene torch to produce a flame with a very high temperature, high enough to melt metals so they could be joined.

Now it's time to start looking at a few larger hydrocarbons, which offer a lot more room for variation. This one has six carbon atoms, all joined in a row by single bonds, so its name is hexane. These atoms can be joined differently, and the new molecule has slightly different properties, so chemists give them different names, even though they still have 6 carbon atoms and 14 hydrogen atoms.

Instead of having all six in a row we could have five in a row, and the last one attached to one of the three carbon atoms that are not at the end of the chain. This is named by calling the molecule pentane (because the long chain has five carbon atoms), and then describing where there is a carbon attached instead of the expected hydrogen atom. This gives two possible molecules, called 2-methylpentane and 3-methylpentane, depending on where that last carbon is attached. There are several more ways in which the atoms can be joined, which are called isomers of hexane. They include 2,2-methyl butane and 2,3-methylbutane, each of which has four carbon atoms in the longest chain.

For each of these arrangements of 6 carbon atoms, it is possible to have a molecule with one or more double or triple bonds (and therefore less hydrogen than in hexane). These names start to get even more complicated, as we need to include more numbers to indicate where in the molecule the double/triple bonds are located. You can just imagine how much detail is needed to systematically describe the molecules when there are several hundred carbon atoms in each one!

The prefix cyclo- in front of the chemical name tells you that the carbon atoms are joined in a ring. If you imagine the hexane molecule from the last question, to form cyclohexane you need to remove a hydrogen atom from each end, then join those two carbon atoms together. The six carbon atoms do not lie flat, but make a 3D shape, with some higher and some lower. There are several ways this can be done, as you can see if you get out a set of molecular models and try to make it work. The shape in the image, called the chair shape, is the most stable arrangement. The other one is called the boat configuration. Molecules arranged in that shape usually end up adjusting themselves to have a chair shape.

Cyclohexane is not found in natural petrochemical sources, but can be manufactured from them. Its main use currently is as part of the process of making nylon. It is also sometimes used as a solvent (as in correction fluids) and a detergent. The main reason for its selection in this quiz was to introduce the next chemical in a logical fashion.

The benzene molecule is the simplest in the group called aromatic hydrocarbons - so called because the earliest ones discovered had distinctive aromas. They share a special kind of attachment between their carbon atoms, called pi-bonding, which is shown in the diagram by a circle inside the ring of carbon atoms. Each carbon atom is shown attached to two carbon atoms and one hydrogen atom, leaving it needing one more connection. This was once shown by having three of the connections in the ring be single bonds, and three of them double bonds, but this didn't agree with the observed chemistry of benzene, which does not undergo the addition reactions that model predicted. The stable ring is now seen as (in layman's terms) a cloud of six electrons being shared around such that each carbon-to-carbon link is effectively halfway between a single bond and a double bond.

Benzene itself is quite toxic, and is mainly used in the production of other materials. The aromatic ring structure, however, is an essential part of many of the molecules on which life as we know it depends: chlorophyll which captures the sun's energy for use as food, hemoglobin which carries oxygen around the body, and DNA, the material that carries the genetic information for living things are just a few examples.

Hydrocarbons are not the only kind of chemical in the field of organic chemistry, of course. This is an example of an alkanol, in which one of the hydrogen atoms of an alkane has been replaced by a hydroxyl (OH) group. The oxygen atom is shown in red. The hooked shape it makes to replace the symmetrical hydrogen means that ethanol has properties that are quite different from those of ethane.

Ethanol, the alcohol found in alcoholic drinks, is also called ethyl alcohol, grain alcohol, drinking alcohol, or just alcohol. It can be used as a fuel, and in industrial production of other chemicals, but is most often encountered as an intoxicant, produced by fermentation of fruits, grains and/or vegetables. It is also used as a sedative and as an antiseptic.

Ethanoic acid is much more commonly called acetic acid (even by chemists), and is the ingredient in vinegar that provides its tang. As the model shows, it has two carbon atoms in each molecule, but one of them has no directly-connected hydrogen atoms. Instead, there is a hydroxyl group, similar to that found in ethanol, and an oxygen atom which is attached by a double bond. This group is called a carboxylic group, shown as -COOH, and is found in all organic acids. When the molecule dissolves in water, the hydrogen on its end is likely to be detached, so the solution becomes acidic.

Carboxylic acids are found in a number of places: methanoic acid (also known as formic acid) is what make insect stings burn, for example. The important group known as amino acids (from which proteins are made) have an amino (NH2) group and an acid group in each molecule. A carboxylic acid with a lot of carbon atoms in it is called a fatty acid, and is an important component of our food.

Now we're starting to get pretty complicated! Ethyl ethanoate is an example of an ester, a chemical that forms when an alcohol and a carboxylic acid react to form one large molecule. On the left of the image you can see what looks like a molecule of ethanoic acid that has lost the hydrogen from its hydroxyl group. On the right is a molecule of ethanol that has lost its OH group, and grabbed hold of the open oxygen atom from the acid's hydroxyl group. The reaction between an alcohol and an acid is called esterification, and the product is an ester (and a molecule of water). The first part of its name shows the alcohol that was involved, the second part the acid, and the ending -oate tells you how they joined.

This molecule, along with others formed from organic acids with only a few carbon atoms, is usually described by its trivial (traditional) name - ethyl acetate. Larger molecules tend to use systematic names. It should be familiar as the main ingredient in many nail polish removers (because it smells better than the alternative, acetone), as well as other solvents. It is also use in the process of removing caffeine from coffee and tea.

Esters are responsible for the aroma of many fruits, such as bananas, pears, pineapples and strawberries. They are also important in the plastics industry - polyesters are made up of many repeating units, each containing at least one ester (COO-) group.