Lewis acids and bases ionic bonding. Classically, the term "Lewis acid" is restricted to trigonal planar species with an empty p orbital, such as BR where R can be an organic substituent or a halide. For the purposes of discussion, even complex compounds such as EtAlCl and AlCl are treated as trigonal planar Lewis acids. Metal ions such as Na, Mg, and Ce, which are invariably complexed with additional ligands, are often sources of coordinatively unsaturated derivatives that form Lewis adducts upon reaction with a Lewis base[citation needed]. Other reactions might simply be referred to as "acid-catalyzed" reactions. Some compounds, such as HO, are
NASA Star and Exoplanet Database NASA Star and Exoplanet Database The NASA Star and Exoplanet Database (NStED) is an on-line astronomical stellar and exoplanet catalog and data service that collates and cross-correlates astronomical data and information on exoplanets and their host stars. NStED is dedicated to collecting and serving important public data sets involved in the search for and characterization of exoplanets and their host stars. The data include stellar parameters (such as positions, magnitudes, and temperatures), exoplanet parameters (such as masses and orbital parameters) and discovery/characterization data (such as published radial velocity curves, photometric light curves, images, and spectra). The NStED collects and serves