Studies of organometallic chemistry in the gas phase can provide substantial quantitative information regarding the interactions of transition metals with a wide variety of covalently and noncovalently bound ligands. In this review, the technique of guided ion beam tandem mass spectrometry for the measurement of thermodynamic information is highlighted. Periodic trends in covalent bonds between first, second, and a few third row transition metals and small ligands are discussed. Periodic trends in covalent versus noncovalent metal ligand bonds are compared and fluctuations in sequential noncovalent bonds (solvation) as a function of different metals are reviewed. In all cases, electronic effects that can be used to understand the various trends are elucidated. Finally, recent results for ligands covalently bound to metal clusters are reviewed. (C) 2003 Elsevier Science B.V. All rights reserved.