usando el concepto de valencia para los elementos S, P Y Br predice las formulas de los compuestos mas simples formados por estos elementos al combinars, cada uno, con el hidrogeno.

c- cold periods in earth's history during which glaciers covered much of the surface.

explanation:

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.