Intro to Chemistry: The Atom

A long time ago, in ancient Greece, a philosopher named Democritus was trying to figure out what matter was made of. He thought that if divided a block of salt in half, then divided it again, and again, and again, that eventually he would reach a point where the salt could no longer be divided. He called this unit, atomos, meaning “indivisible.”

Democritus was astonishingly close, although he supposed that all of these atoms were identical. In reality, there are at least 118 known types of atoms, called elements. In Physiology, we really only deal with a handful of them: Hydrogen, Carbon, Oxygen, and Nitrogen. You’ll also see a few others, including Calcium, Phosphorous, Sodium, Potassium, and Chloride.

An atom is made up of 3 types of subatomic particles:

  • Protons — these particles are positively charged and they’re found in the nucleus (center) of an atom
  • Neutrons — these particles have no charge (they’re neutral) and are also found in the nucleus of an atom
  • Electrons — these particles have a negative charge and are found orbiting around the nucleus

Normally, the number of electrons (negative charges) and protons (positive charges) in an atom are the same, so the charge of the atom is balanced.

If something happens and an atom gains or loses electrons, then the atom will have a positive or negative charge. For example, if Lithium has 3 protons (+) and 3 electrons (-), the charge of the atom is neutral. But if it loses an electron (-), then the Lithium atom will have a positive charge. This point confuses a lot of people so take a moment to take it in — if you lose a negative charge, you become positive.

Atoms (or molecules) that have a charge are called ions. Positively charged ions are called cations and negatively charged ions are called anions.

In the Lithium example, we asked,”what would happen if an atom gained or lost electrons?” But what if it gained or lost protons? Well, it wouldn’t. Sort of. If an atom of an element gains or loses a proton, then it is no longer an atom of that element. It becomes a different element.

The number of protons in an atom determines which element it is. In fact, if you look at the Periodic Table of Elements, they’re arranged by their atomic number, which is the number of protons each element has. Let’s take Carbon and Nitrogen as an example. Carbon has 6 protons and Nitrogen has 7. If Carbon gained a proton, it would become Nitrogen. If Nitrogen lost a proton, it would become Carbon. It’s not very common for atoms to gain or lose protons, but it does happen, for example, when solar radiation excites Nitrogen to lose a proton and become radioactive Carbon-14.

So by now, you have to be asking “what happens when an atom gains or loses neutrons?” Well, it becomes an isotope. The textbook tells us that isotopes are atoms of an element that differ in the number of neutrons. You could think about isotopes as different versions of an element. If we say that Windows and MacOS are different elements, then Windows 7 and Windows 10 would be different isotopes of Windows.

The weight of an atom is called its atomic weight or atomic mass and it’s measured in units called Atomic Mass Units (AMU). 1 AMU is equal to the weight of normal Hydrogen atom. Protons and neutrons each weigh 1 AMU. We don’t factor in electrons because they have very little mass.

Carbon, which has 6 protons and (normally) 6 neutrons, weighs 12 AMU. This isotope of Carbon is the most common and it’s known as Carbon-12. Different isotopes of Carbon can have different numbers of neutrons. For instance, Carbon-13 has 7 neutrons and Carbon-14 has 8 neutrons. Remember, when we see different isotopes of an element, only the number of neutrons will change. The number of protons cannot change, because then it would be a different element.

That’s it for now! Join us next time when we cover how these atoms are involved in reactions and build molecules.

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