The H5O2 group can behave very differently in different surroundings. When partially charged, with the remainder of the charge on surrounding groups, it can have a short central hydrogen bond, with O-O distance <2.5 Angstrom. A different arrangement of surrounding groups can produce a normal hydrogen bond, with O-distance >2.7 Angstrom. The transition is, for some systems, very abrupt. In the cases we discuss here, there is an example of a set of conditions in which this abrupt transition occurs. There is also a case in which intermediate values of the central hydrogen bond occur, but this behaves as though these values remain on one side of the transition point. The switch is effected by small changes in the position of the surrounding groups. To study this, several sets of four groups were used to surround the H5O2 group. Density functional calculations were carried out on the system, with the surrounding groups fixed in each of several positions, and the H5O2 group optimized. Some configurations produced short bonds, some normal bonds. The most instructive set of surrounding groups was simply four Cl- ions, with protons added; the protons both adjusted charge and affected bonding. When the total charge on the system was -2 (including the H5O2 group charge), either a normal or a short bond could be produced, depending on the distance of the Cl- ion from the H5O2 group. The change from normal to short occurred over a change in Cl-position of 0.005 Angstrom. Calculations of bond order, and with the atoms-in-molecules technique, gave consistent results. When the total charge was -3, changes in bond length, bond order, and bonding were smooth, and the system appeared to remain on one side of the transition. It appears that there exist conditions under which the H5O2 group can act as a chemical switch and that addition of a proton can activate the switch.