why are some elements naturally radioactive?

Answer 1

The element is determined by the number of protons in the nucleus, for example carbon always has 6 protons, no more, no less. The number of neutrons in the nucleus is more flexible. Each element can have several different isotopes (variations of the same element with a different number of neutrons.) If the atom has too many neutrons - or not enough - it will not be stable, and it will at some point decay, in other words, it is radioactive.

Most elements have at least one stable isotope, for example, carbon is stable with 6 neutrons or with 7. (Most carbon has 6.) Carbon with 8 neutrons is not stable and it is this carbon (Carbon-14) which is used for radiocarbon dating.

With heavier elements, the nucleus gets larger, and the middle ground between too many neutrons and not enough is harder to come by; the heaviest elements have no stable isotopes, all are radioactive. The very heaviest elements discovered so far decay in a fraction of a second and have been observed only in the lab where they were manufactured.

Answer 2

The neutrons and protons that constitute nuclei, as well as other particles that may approach them, are governed by several interactions. The strong nuclear force, not observed at the familiar macroscopic scale, is the most powerful force over subatomic distances. The electrostatic force is also significant. Of lesser importance is the weak nuclear force.

The interplay of these forces is very complex. Some configurations of the particles in a nucleus have the property that, should they shift ever so slightly, the particles could fall into a lower-energy arrangement. One might draw an analogy with a snowfield on a mountain: while friction between the snow crystals can support the snow's weight, a disturbance may faciliate the path to lower potential energy (towards the ground) and an avalanche results.

Therefore some elements are radioactive.

Answer 3

for simple, there's some elements have unstable electrons inside of them, the electrons change or move to the other orbital, when the electrons move out or excite of their own orbital, they loose some energy which are radioactive ray.