Why Are Elements Unstable?

Why some elements are radioactive (unstable). When the atoms of an element have extra neutrons or protons it creates extra energy in the nucleus and causes the atom to become unbalanced or unstable.

What makes an element stable or unstable?

An atom is stable if the forces among the particles that makeup the nucleus are balanced. An atom is unstable (radioactive) if these forces are unbalanced; if the nucleus has an excess of internal energy. Instability of an atom's nucleus may result from an excess of either neutrons or protons.

Why higher elements are unstable?

Many of the elements heavier than lead have nuclei so large that they are fairly unstable. Due to the instability, over time they eject a neutron or proton, or a neutron in the nucleus decays into a proton and electron. This is called radioactive decay, since the original nucleus is "decaying" into a more stable one.