Let’s see what you know about the most basic chemistry… What does this formula represent? H-I-J-K-L-M-N-O Don’t you recognise it? It is water. It’s H to O (H2O)…
Okay, let’s build on that… Two chemists walk into a restaurant and the first one says “I’ll have some H2O” and the second chemist says, “Yeah, I’ll have some H2O, too” drank it, started foaming at the mouth and then threw up. Why? H2O2 is Hydrogen Peroxide…
What’s in an Atom?
Atoms usually have Protons (positively charged particles) and Neutrons (uncharged particles) in the centre. How many determines their atomic mass. Hanging around this nucleus are the electrons that exist in a cloud-like structure where they pop in to and out of existence without actually orbiting. We used to think they went in circles like the planets going around the Sun but Quantum Theory showed us differently. Google® that later for fun!
The number of Protons tell us what an element is. If it has 22 Protons, it’s Titanium; if it has only 1, then it is Hydrogen. The number of Neutrons can change, but they don’t affect the identity of the element. The Atomic Mass is the average mass of the number of Protons and Neutrons found in the nucleus.
Okay let’s get serious and have a look at the Periodic Table. It is a grid, and it reads from left to right, or up and down, depending on what information you are looking for.
Element #1 is Hydrogen and it is in the top left corner, the first element in the pink row (or Period) #1. The next element is Helium away over in column 18 in the top right corner. It is very far away. Each element in a period has the same number of electron shells or orbitals. Hydrogen has one orbital and so does Helium, but they’re the only elements that only have one, so they get their own row. We’ll talk about why it’s so far away in a moment.
The next Period (light blue) has eight different elements in it, and they all have two electron shells or two orbitals. Do you see where this is going? Each new periodic row has one more orbital than the previous period. The third row (yellow), or period, has eight elements that each have three orbitals. Currently we have only discovered seven orbitals so that is why there are seven rows.
Period 6 (cream) and Period 7 (Blue) have some slightly different elements that are listed separately at the bottom. They’re part of the same row but we keep them aside for convenience.
When we look at the Periodic Table from top to bottom we are looking at Groups.
In the illustration the first group is red and every element in that group has the same number of electrons in its outer electron shell or orbital. Group 1 has one electron; group 2 has two electrons; group 3 has…you guessed it… 3 electrons! It goes on this way all the way to group 18, which has…? Right, 18! But there is an exception in column 18… Helium is listed in column 18 because that is where all the other noble gasses are. They all have 18 electrons in their outer shell except for poor Helium. Having one odd noble gas in column two was awkward so we agreed it should be in 18 with the rest.
These outermost electrons are called valance electrons and are responsible for the chemical bonds with other elements. Again, there are exceptions. The Yellow zone in the centre is filled with Transitional Elements and they actually allow the outer two orbitals to share electrons with other elements. So group 3 usually has three electrons and group 4 usually has 4 electrons, etc….
This tells you some simple things about how to read a Periodic Table. The table below is less flooded with colour so you can see the letters telling you what the elements are.
The letters come from history, and are traditional. If you were looking for the element Lead, you would need to know that alchemists originally called it Plumbum so its letters are Pb. It has 82 protons. See if you can find it on the chart.
Many of the symbols make sense. Hydrogen is H; Helium is He; Carbon is C; Nitrogen is N; Oxygen, Fluorine and Neon are O, F, and NE, respectively. But there are odd ones like Sodium (Na), Potassium (K), Gold (Au), Silver (Ag), and Mercury (Hg) that you will have to remember.
And of course there is the element in Period 3, at Group 12… That’s the Element of Surprise! Now go learn some chemistry and have fun! And come back to check on this table… periodically…