The ONIOM method is used to study the addition of H and F atoms to the side of a (10,0) carbon nanotube. The entire model uses 200 carbon atoms, while the accurate section includes 24 carbon atoms. The B3LYP functional is used for the accurate calculation of the reaction site, while the Universal Force Field (UFF) is used to describe the neighboring atoms. The F atoms appear to favor bonding next to existing F atoms. Unlike the addition of fluorine, the addition of two or four H atoms to a (10,0) tube is computed to be endothermic.