Chemical Bonding:

As begin in the earlier, the number of electrons within the outer, or valence, shell determines the associative activity of the element. An arrangement of electrons within the outer shell explains why a few components are chemically extremely active, a few are not extremely active, and others are inert. In common, the fewer electrons an element must gain, lose, or share to reach a stable shell structure, the more chemically active the components are. The likelihood of elements forming compounds is tightly influenced through the completion of the valence shell and through the stability of a resulting molecule. A more stable the resulting molecules are, the more likely these molecules are to form. For instance, an atom which "needs" two electrons to totally fill the valence shell would rather react along with another atom that must provide up two electrons to convince its valence.

In that case of H⁺ + Br^-, that is likely to take place since the exchange would satisfy the requirement of both atoms. While there is far more to assume than only the number of valence electrons, that is a good rule of thumb.

If the atom required two electrons and just picked up one, it would still actively find out a further electron.  A reaction of H⁺ + Te^-2 is far less such as to take place since the resulting molecule would still have an incomplete valence shell. Certainly, the combining of two atoms, while both needs to release or gain electrons, might take place (for instance; H₂ or O₂) but is less possible while other atoms are available.

Atoms are bonded or joined together by this interaction of their electrons.  Those are various categories of chemical bonds which hold atoms together; three will be elaborate, covalent, ionic, and metallic.