What are isotopes? You may have heard of them many times in movies when they are talking about nuclear weapons, but isotopes are not just unstable atoms used for undergoing nuclear fission (the splitting of an atom’s nucleus), they are, simply put, atoms that have the same number of protons, but vary in their number of neutrons.

Protons are the subatomic particles that define an atom, if an atom loses or gains a proton, they will become a different element. For example, if a hydrogen atom gains a proton through the process of nuclear fusion (the bringing together or fusing of 2 atomic nuclei), it will become Helium, an isotope of helium to be exact. Because Helium has 2 protons, 2 electrons, and 2 neutrons but Hydrogen has no neutrons in its nucleus. Thus, if we bring 2 hydrogen nuclei together we get a helium atom with no neutrons but 2 protons and 2 electrons.

If an atom loses or gains an electron it becomes an ion. If the atom gains an electron it, considering the atom has the same amount of electrons as protons to begin with, becomes a negatively charged ion and if it loses an electron it, again considering the same idea, becomes a positively charged ion. Ions, unlike atoms that change in proton number, stay the same element. The number of protons in an element defines that element because of this. If an atom gains or loses neutrons, it doesn’t gain or lose charge and doesn’t become another atom. Instead it becomes an isotope of an atom.

Isotopes have different mass properties because gaining neutrons will add mass and losing neutrons will lose mass. When looking at an element on the periodic table, you will see 3 numbers, these are the mass number, the atomic number, and the atomic weight/mass. Lets use Carbon as an example. Carbon’s symbol is C.

Source:https://steemit.com/science/ https://steemit.com/science/@elemenya/chemistry-express-the-weight-of-protons-neutrons-and-electrons

As you can see, the mass number is to the top left of the atom’s symbol, the atomic number is to the bottom left of the atom’s symbol, and the atomic mass/weight is beneath it. The atomic number is the number of protons in the atom, in this carbon isotope’s case it’s 12. The mass number is the combined number of protons and neutrons in the atom. Before I explain the atomic mass, it is important to understand the measurement of mass on this scale. Scientists use a unit called an atomic mass unit (amu). 1 proton weighs approximately 1.007 amu and 1 neutron weighs approximately 1.009 amu. 1 electron weighs almost a measly 0.00055 amu.

The atomic mass shown below Carbon’s symbol is the weighted average mass of all the natural occurring isotopes of an atom. Carbon has 3 naturally occurring isotopes: Carbon-12, Carbon-13, and Carbon-14. These can all be abbreviated as C-12 or C-13. With just the element’s symbol, a dash sign, and then the mass number. Showing by the atomic weight/mass, C-12 is the most abundant isotope in nature at percentage of about 98.9%, C-13 is at about 1.1% abundance, and C-14 is about 0.0001% abundance.

C-12 and C-13 are stable isotopes meaning that their neutrons will not emit energy or subatomic particles. C-14 is known as unstable and radioactive, meaning that the neutrons in its nucleus will decay into subatomic particles or light waves/photons and release energy. Scientists have been able to measure the ages of fossils by using the half life, or the amount of time for half of the neutrons in every one of a particular isotope to decay. 

Scientists believe that the ratio of protons to neutrons determines the stability of the nucleus. Too many or too few neutrons leads to an unstable nucleus. As the neutrons in the nucleus decay, the nucleus will become more stable.

One more thing about isotopes that is really important to understand: There is no “original” isotope, there is only a difference in abundance for isotopes. What is meant by this is that every atom is an isotope of its element. As long as the atom has the same number of protons as its element shows, it is an isotope. This is very important to understand as many people have gotten it mixed up.