For students, understanding the general architecture of the atom and the roles played by the main constituents of the atom in determining the properties of materials now becomes relevant.

The amount of carbon-14 gradually decreases through radioactive beta decay with a half-life of 5,730 years.

So, scientists can estimate the age of the fossil by looking at the level of decay in its radioactive carbon.

For carbon, there are a lot of C-12, a couple of C-13, and a few C-14 atoms.

When you average out all of the masses, you get a number that is a little bit higher than 12 (the weight of a C-12 atom).

We have already learned that ions are atoms that are either missing or have extra electrons. They are just a little different from every other atom of the same element. Electrons don't have much of a mass when compared to a neutron or proton.

Let's say an atom is missing a neutron or has an extra neutron. An atom is still the same element if it is missing an electron. For example, there are a lot of carbon (C) atoms in the Universe. Atomic masses are calculated by figuring out the amounts of each type of atom and isotope there are in the Universe.The second lesson, Radioactive Decay: A Sweet Simulation of Half-life, introduces the idea of half-life.By the end of the 8th grade, students should know that all matter is made up of atoms, which are far too small to see directly through a microscope.This lesson is the third in a three-part series about the nucleus, isotopes, and radioactive decay.The first lesson, Isotopes of Pennies, deals with isotopes and atomic mass.However, radioisotope dating may not work so well in the future.