Atoms of different elements unite during chemical changes to produce new substances called compounds.

Here's why:

* Chemical changes involve the breaking and forming of chemical bonds between atoms.

* Elements are pure substances made of only one type of atom.

* When atoms of different elements bond together, they form a compound, which has different properties than the original elements.

For example, when sodium (Na) and chlorine (Cl) react, they form sodium chloride (NaCl), commonly known as table salt. Salt has entirely different properties than either sodium or chlorine.