The electronic and geometrical structures of the ground and excited states of the homonuclear Sc-2, mixed ScTi, ScV, ScCr, ScMn, ScFe, ScCo, ScNi, ScCu, and ScZn 3d-metal dimers and their anions have been calculated using the density functional theory with generalized gradient approximation for the exchange-correlation potential. The ground states of the neutral dimers are found to be (5)Sigma (-)(u) (Sc-2), (6)Sigma (+) (ScTi), (7)Sigma (+) (ScV), (4)Sigma (+) (ScCr), (3)Sigma (+) (ScMn), (2)Delta (ScFe), (1)Sigma (+) (ScCo), (2)Sigma (+) (ScNi), (3)Delta (ScCu), and (4)Sigma (+) (ScZn). A natural bond analysis reveals an antiferrimagnetic spin coupling in the ground states of ScCr, ScMn, and ScFe. This is due to the electron transfer from Sc to the opposite atom and specific bond formations. While each dimer has a unique chemical bonding pattern, most curious is the localization of two 4s electrons at both atomic sites in the ground (5)Sigma (-)(u) state of Sc-2, which leads to formation of two lone pairs and the bonding scheme: (3d + 3d)(alpha)(3)(4s + 4s)(beta)(1). No appreciable sd hybridization is found for the ground states of the ScX dimers except for ScNi. Even though the electron affinities of the ScX dimers are relatively low and do not exceed 1 eV, each ScX- (except ScCo-) possesses at least two states stable towards detachment of an extra electron.