What part of the atom determines if it will combine or break apart from other substances?

The atom consist of three parts, proton, neutron and electrons. The electrons determine that i will combine or beak from other substances.

Explanation:

The atom consist of three parts which are following

proton neutron electron

The proton and neutron form nucleus of an atom. It is present at center of an atom. They have positive charges, while electrons remained outside the nucleus in particular energy levels or shell around the nucleus.

During combination or breaking of substances, only arrangements of electrons take place. The valence shell electrons decide whether they have to combine or not, while nucleus remained unchanged during any reactions.