Hydrogen's sole electron occupies the 1s orbital but can be excited to the 4p orbital. list all the orbitals this electron might occupy on its way back to its ground state.

gold is my favorite solid.

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.