Radioactive decay dating
The only way that this can happen is by changing the number of protons in the nucleus (an element is defined by its number of protons).
There are a number of ways that this can happen and when it does, the atom is forever changed.
Statistical probablity is the only thing we can know exactly.
Often students get bogged down in the fact that they don't "understand" how and why radioactive elements decay and miss the whole point of this exercise.
Most students don't really know how isotopes are used to determine age.
And once that first kernel pops, it will never be a kernel again..is forever changed! ) Teaching example using popcorn to teach radioactive decay "A variety of a chemical element (strictly, of one particular element) which is distinguished from the other varieties of the element by a different mass number but shares the same atomic number and chemical properties (and so occupies the same position in the periodic table)." That definition may not mean anything to them.If they can begin to comprehend that it is random and spontaneous, they end up feeling less nervous about the whole thing.