The Ties That Bind - Chemical Bonds

Do you remember Tinkertoys? They were made out of wood and had a spool with holes into which you could insert sticks to make almost anything. In fact, the set was designed and patented to enable the construction of 45-45-90 degree right triangles based on the Pythagorean theorem (The sum of the squares of the sides of a triangle equals the square of the hypotenuse: a² + b² = c²). This design allowed for the construction of some very complex machines, including a tic-tac-toe playing computer and a robot. Elements can be combined together much like Tinkertoys, based on how full their outer electron shells are, their polarity and ionic states, and Hydrogen's affinity for them. They can create one to many bonds, with each other or with other elements, following specific rules. Just as in the case with Tinkertoys where you had to use specific colored sticks to build a certain shape, with the formation of compounds or molecules from several atoms, you have to use elements that fit the rules to connect to one another. Each element will only bond with certain other elements and only under certain conditions. Even with the rules for combining elements together, the possibilities are endless. As we mentioned last time, just considering biological compounds, over ten million different molecules have already been classified.

Elements form bonds with other elements at the atomic level. These bonds exist in three main types - ionic, covalent and hydrogen. Other types of bonds do occur but these three will be our focus.

Hydrogen bonds are not really chemical bonds but more of a weak attraction between hydrogen and another element in a compound that helps to link molecules together loosely or in the case of large molecules like proteins, helps to define their structure. Typically, in living systems, such bonds form between Hydrogen and Oxygen or Nitrogen. Each of the elements in the bond must also be covalently bonded to another atom. Water forms Hydrogen bonds extensively between the Hydrogen of one molecule and the Oxygen of another. Due to the nature of these bonds Water (H₂O) is a liquid at room temperature and has a much higher boiling point than that of the other Group 16 Hydride, Hydrogen Sulfide (H₂S), that does not form Hydrogen bonds and is a gas at room temperature.

Ionic bonds are generally between two atoms of opposite polarity, like Na⁺ and Cl^-. Ionic bonds are not a bond between two specific atoms of opposite charge but are a bond between a positively charged atom or ion with a group of negatively charged ions surrounding it. Thus, in the case of NaCl or Salt, the molecule will form a lattice of positively charged Na⁺ ions (gray) surrounded by negatively charged Cl^- ions (green) that are themselves surrounded by positively charged NA⁺ ions. A cubic structure will be the result. Typically the ionic bond is broken when the molecule is dissolved in water or other polar solvent and the molecules of the solvent surround the electrically charged atoms.

Covalent bonds are true bonds where the unpaired electrons are fully shared between the two atoms. These bonds are between two specific atoms of the bonding elements. These are generally the strongest type of bonds. An example would be the double bonds between Carbon and each atom of Oxygen in Carbon Dioxide or CO₂ (O=C=O).

A molecule can have either Ionic bonds as in Salt (NaCl) or covalent bonds as in Carbon Dioxide (CO₂) or both as in Sodium Cyanide (NaCN) where the Na⁺ is bonded to the CN^- with an ionic bond and the Carbon is bonded to the Nitrogen with three covalent bonds. Only molecules with covalent bonds and containing Hydrogen can be Hydrogen bond donors. Hydrogen bond acceptors also have covalent bonds but do not have to contain Hydrogen.

Using these three types of bonds, God has created a vast array of biological molecules from just a handful of elements. The DNA molecule contains just Carbon, Nitrogen, Hydrogen, Oxygen and Phosphorus and yet it contains all of the information necessary to produce life as we know it. Could this (DNA) have happened randomly? With its intricate design and elegant function, I think not.