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 direct access to frequently accessed tables: NStED also serves photometric time-series data from surveys that aim to discover transiting exoplanets such as "Kepler" and the CoRoT. NStED provides access to over 500,000 light curves from space and ground-based exoplanet transit survey programs, including: The transit survey data are linked to an online periodogram service that can be used to search for periods in the transit survey data sets. A user can also upload their own time series data to search for periods in their own data. The planetary orbital parameters are linked to an online transit ephemeris prediction tool which