Why do atoms combine with each other?

Most interactions among atoms take place in the outermost shell of each atom. The number of each electron in this shell determines how an atom combines with other atoms to form compounds. When atoms combine they gain, lose or share electrons in such a way that the outer shells become chemically complete.

Atoms combine with each other to form various compounds.

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1. they vary with a higher number because boiling is way hotter than melting