You know that you’re surrounded by stuff – stuff that you can see and stuff that you can’t see. We already know that there are trillions of bacteria, viruses, animals, plants, and fungi around. And we can see and touch all of those other things that make up our world: chairs, desks, pens, pencils, gum that someone dropped on the ground, a note from that cute boy/girl, etc. Plus, there’s even the air around us that’s made up of stuff. All of this stuff is ultimately made up of atoms, so let’s start there.
Atom comes from a Greek word that means “cannot be divided.” Unluckily for the Greeks, we now know that we can split atoms, but that’s a completely different story. However, the first scientists to discover the atoms in the world around us started to try to figure out what it all meant. So they organized the atoms by their elemental form, in a table. This become, thanks to a certain Mr. Mendeleev, the Periodic Table of the Elements.
If you understand the Periodic Table of the Elements thoroughly, you can actually sound very smart. The columns of the Periodic Table all have elements that are in the same family (or group) and share very similar properties. Gold, silver and copper are all in the same family. Neon, argon, krypton, and xenon are all in the same family and are used in “neon” fluorescent lights. The rows of the periodic table also show patterns. There are certain properties of elements that change in a predictable way over a period.
How is the order of the periodic table determined? Well, all atoms have inside of them several different kinds of particles. The ones that we’re most concerned about are protons, neutrons, and electrons. Neutrons are the heaviest particles and have no charge, while protons are slightly lighter but have a positive charge. You can find neutrons and protons in the nucleus of an atom. But you won’t find electrons anywhere near the nucleus. Electrons are way outside the nucleus and are found in “energy levels” around the nucleus. This sounds complicated, but basically you can’t predict exactly where an electron is going to be at any one time, but you know it has to be in a certain region. Electrons have almost no mass and have a negative charge.
However, the most important of these particles is the proton. Sorry, neutron. Sorry, little electrons. You know, you’re cute and everything, but you’re no match for the mighty positive proton. Just by an atom gaining or losing a proton, all of the properties of the entire atom change. In fact, you can turn hydrogen into helium by giving hydrogen one more proton; oxygen turns into useless nitrogen with one less proton; gold becomes worthless as ??? with one more proton. It’s a good thing this doesn’t happen often, which is probably why scientists decided that the number of protons would equal the atomic number.
So now you can look at an element on the Periodic Table and instantly determine how many protons it has: Carbon, with a chemical symbol of C has 6, hydrogen (H) has 1, and Uranium (U) has 92 protons. Bam! Now onto another number on the Periodic Table, the number on the bottom. This is the atomic weight, which means that amount that the average atom of that element weighs. This number is determined by averaging out the weights of all of the different types of each kind of atom. It is slightly different than the atomic mass, which you can find by adding up the number of protons and neutrons for a particular atom.
Depending on the family (or group) that an atom is found in, then its electron configuration will be slightly different. Reading from left to right, every time you start a period, that element has one electron in the last energy level. For the first three periods, every time you go one atom to the right, then you add another electron. For example, lithium has 1 electron in the last energy level, beryllium has 2, boron has 3, carbon 4, nitrogen 5, oxygen 6, fluorine 7 and neon 8.