The Handy Chemistry Answer Book. Justin P. Lomont

a living cell, he also discovered the elements beryllium (independently discovered by Antoine Bussy), silicon, aluminum, yttrium, and titanium. In case that wasn’t enough to cement his position in the annals of chemistry, he also discovered that meteorites contained organic compounds and developed a process to purify nickel.

      How many bonds can carbon form?

      Carbon has four electrons available for bonding with other atoms. When carbon is bonded to four other atoms, they are arranged in a tetrahedral geometry. These two simple bonding rules have important consequences, as we’ll see in this chapter.

      What types of bonds can carbon form?

      Carbon can form single (σ) or double (π) bonds to other elements. Double bonds use two of carbon’s four available electrons, so carbon can form two double bonds (like carbon dioxide, CO₂), or one double bond and two single bonds (like formaldehyde, H₂CO), or four single bonds (like methane, CH₄).

      Can carbon form more than one π-bond?

      Yes, if two carbon atoms form one σ and two π bonds (for a total of three bonds, known as a triple bond), the group is called an alkyne. The simplest alkyne is acetylene (C₂H₂). Welding torches use a combination of oxygen and acetylene to reach temperatures of over 6000 °F (3300 °C).

      What is the shape of a carbon-carbon double bond?

      The geometry of the carbon atoms in double bonds is planar. This shape comes from the hybridization of the carbon atom, which is sp² (one p orbital is not involved in forming single bonds). To get a bonding interaction between these two remaining p-orbitals, they have to overlap in space. So in a molecule like ethylene (C₂H₄), all of the hydrogen atoms are located in the same plane.

      What are hydrocarbons, and how many different ones are there?

      Hydrocarbons, as you might have figured out from the name, are molecules that contain only hydrogen and carbon atoms. There are literally an infinite number of ways to arrange these two elements together, especially if you include polymers (see “Polymer Chemistry”). Hydrocarbons are important molecules. Different sizes and types of hydrocarbons are known as natural gas, gasoline, waxes (like candles), and plastics.

      How do chemists name so many different hydrocarbons?

      With a bunch of rules! Let’s start with just straight chains of carbon atoms. Here we just need to define how many carbon atoms there are in the molecule. If the molecule doesn’t have any double bonds, we use the suffix “-ane.” The prefix indicates how many carbon atoms there are. Most of these prefixes are based on Greek numbers (one is Latin, and a few are just weird). Collectively, these molecules are called alkanes.

      Are hydrocarbons always straight chains of carbon atoms?

      No. There could be carbon atoms attached to the linear chains we talked about in the previous question. Let’s learn the next step in naming alkanes and have a look.

      First, we need to define the names of branches (see graphic, next page). Chemists use the same prefixes to indicate the length of the branch, but now the suffix is “-yl” instead of “-ane.” So methane (CH₄), when it’s a branch off of a chain of carbon atoms, becomes methyl (-CH₃), ethane (CH₃CH₃) becomes ethyl (-CH₂CH₃), and so on.

      Next we have to indicate where along the main carbon chain the branch point is. This part is pretty simple—just number the carbon atoms and put this number before the name of the branch. So if you had an eight-carbon chain (octane) with a two-carbon branch (ethyloctane) on the third carbon from the end, it would be called 3-ethyloctane and look like this:

      Hydrocarbons with additional atoms attached to linear chains have suffixes ending in “-yl” instead of “-ane.” Here are some examples.

      There are a lot more rules to naming organic compounds, but that’s enough for now.

      Can carbon chains form rings, too?

      Yes—chains of carbon atoms can connect back to themselves, forming rings of atoms. The prefix cyclo- is added to the name of the linear carbon chain to indicate that a ring is present (so hexane becomes cyclohexane). The chemistry ring structures can be different than their linear cousins because of the added energy that some rings contain. We know that sp³-hybridized atoms like to form bonds that are separated by 109.5°. The more that a ring forces those bonds to deviate from that ideal angle, the more energy (called ring strain) that is released when that ring is opened during a chemical reaction.

What is the structure of diamond?

      Diamond has a repeating structure of carbon atoms in which all the atoms are bonded to four others in a tetrahedral geometry. It’s easiest to see if we first look at the structure of cyclohexane, a ring (cyclo-) of six carbon atoms (-hex-), with no double bonds (-ane).

      If we repeat the structure of cyclohexane over and over, we arrive at the structure for diamond.

      What is charcoal?

      Charcoal is made of carbon and ash and is formed when water and other substances are removed from animals or plants. It can be produced by heating wood or other biologically derived materials in the absence of oxygen.

      What is a heteroatom?

      A heteroatom is any atom that is not a carbon or hydrogen atom. Some examples of typical heteroatoms include oxygen, sulfur, nitrogen, phosphorus, chlorine, bromine, and iodine, though anything other than carbon or hydrogen fits the definition.

      What is a chalcogen?

      A chalcogen is an element in group 16 on the periodic table. This includes oxygen, sulfur, selenium, tellurium, polonium, and livermorium. This name comes from the Greek word meaning “copper-former,” and has its origins in the fact that some of these elements tend to coordinate to metals to form compounds with metals in ores.

      The structure of a diamond crystal.

      What is a cation?

      A cation is a positively charged atom or molecule. Cations have a larger number of protons than electrons, such that they have a net positive charge.

      What is an anion?

      An anion is a negatively charged atom or molecule. Anions have a larger number of electrons than protons such that they have a net negative charge.

      What is a free radical?

      A free radical is an atom or molecule that contains unpaired electrons in one (or more) of its orbitals. Typically these species will be highly reactive