Seeing the chemical ties that bind (Science Advent 4)

(Every day until December 25, I’m posting a science-related image and description.)

Day 4

Hydrogen bonds as imaged by an atomic force microscope. [Credit: Science]

Chemical bonds in the molecule 8-hydroxyquinoline as imaged by an atomic force microscope, with a diagram to show the positions of the atoms and their bonds. The dotted lines in that diagram are the hydrogen bonds; the red dots are oxygen, the gray are carbon, the blue are nitrogen, and the white are hydrogen. [Credit: Science]

Chemistry at its heart is the formation and breaking of electrical bonds between atoms. This happens as electrons are shared between atoms or redistributed due to interactions. Despite the many elements and molecules they make, and all the marvelous complexity of chemistry, there are only three basic types of chemical bonds: covalent (where an electron is shared between two atoms), ionic (where an electron is swapped), and hydrogen.

Hydrogen bonds are responsible for the structure of ice (including snowflakes!), DNA, and a wealth of other important things. Here’s how it works: a molecule containing hydrogen shares electrons unequally, giving the hydrogen a slight positive charge and the other atom (such as oxygen or nitrogen) a slight negative charge. Two of these molecules can then attract each other, with the positive bump on one molecule bonding with the negative bump on another.

The image above shows the molecule 8-hydroxyquinoline, which involves several atom types structured in smaller molecules bound together by hydrogen bonds. The image was produced by an atomic force microscope, which maps the distribution of electric charge as it repels atoms on the microscope tip. (Atomic force microscopes are very cool, and worthy of a later blog post!) What’s fascinating is that the picture of the molecule produced this way is remarkably similar to the schematic diagram next to it. Our mental picture of the shape of molecules is actually the way they “look”, if we could see with electrons.



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