Chemical Reactions and the Use of Arrows

When some chemical reactions occur, one reactant molecule is transformed into one product molecule. To represent the movement of valance electrons in a chemical process arrows are drawn on the molecule. A single headed arrow on a molecule (below in blue) represents movement of a single electron (radical) involved in making or breaking a bond. An example of a chemical reaction with arrows drawn to indicate breaking and forming bonds can be seen below.

In the molecules in the previous picture two electrons in molecule A come together and are shared between the two end carbon atoms to creat a new bond and form a six membered ring in molecule B. Two other electrons, one from each triple bond, move to two carbon atoms where they exist as radicals.