Why are atoms of lithium, sodium, and potassium almost neverfound alone in nature

 The Alkali elements are so reactive that they are never found alone in nature

These three metals- called the alkali metals- have one electron in their outer shell. Since all atoms want to be stable, it try's to lose this electron. They are very reactive, and so will be found in compounds or mixtures, such as sodium chloride (table salt!)

Hope this helps:)

Yes, endothermic means it turns cold. and some chemical changes include change of tempature.