If sucrose (c12h22o11) is composed of glucose (c6h12o6) and fructose (c6h12o6) shouldn't the molecular formula be (c12h24o12). what happened to the missing hydrogen and oxygen atoms?

This is a type of condensation reaction.

Explanation:  Condensation reactions are the reactions in which two small molecules combine to form a larger molecules producing a small molecule such as ,   etc. as a byproduct.

Glucose( and Fructose() are the simplest carbohydrates and when they combine to produce Sucrose() and release water() as a byproduct.

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.