The structural, energetic and electronic properties of D-5h C-50 before and after passivation by H and Cl are investigated using density functional theory method with GGA and LDA exchange-correlation functional. The results show that H or Cl addition can lead to structural changes and energetic stabilization. Addition reactions also increase the HOMO-LUMO gaps of C-50 derivatives which will make them chemically more stable. The passivation effect of local addition has globality character which not only partly releases the strain of the region near the addition locations of C4 site but also remarkably reduces the strain of other areas away from addition sites. The preferment of C4 site addition is confirmed by single atom additions and by computations on 144 isomers of C-50 H-10 with one or two H atoms added to non-equatorial sites. (c) 2006 Elsevier B.V. All rights reserved.