What is the Periodic Table?

The New Periodic Table - by European Chemical Society

The periodic table of elements is used to display all of the known atomic elements. Each square on the table relates to one element, and the position and colour of each element shows what kind of element it is, its properties, and how it relates to other elements.

There is a lot of information in even the simplest periodic table. To make it easier to understand, we’re going to break it down from the very beginning:

What Is an Atomic Element?
Atoms are the building blocks of everything around you, from your clothes, to the trees outside, to you!

Not all atoms are the same, however. Atoms themselves are made out of things called sub-atomic particles (basically “things smaller than an atom”).

The number and kind of sub-atomic particle determines what kind of element an atom will be. Because of this, different atomic elements have different properties.

For example, let’s look at two elements you can use the same way, with different results: oxygen, and helium. These are both gasses at room temperature, and you can breathe them both in.

However, you probably know that you need oxygen to live, while helium will just make your voice squeaky. They’re both elements, they’re both gasses, but they have very different properties because of how their atoms are made.

Atomic elements can be added together to form molecules. You can make molecules by multiplying a single element, or you can add lots of different elements together.

For example, when you add one atom of oxygen with two atoms of hydrogen, you get water.

Part of the periodic table is arranging these elements in a way that gives someone an idea about the properties of the different elements very quickly.

What Information is On Each Element?
When you look at the periodic table of elements, you see a lot of squares, or “cells”. Each cell contains information about a single element.

Some periodic tables offer more detailed information than others, but they all have certain basic elements. These are the atomic symbol, the atomic number, and the atomic weight. Most periodic tables list the element name, but some don’t due to size restrictions.

What Is the Atomic Symbol?
The thing you’ll first notice is the atomic symbol, which is usually one or two large, bold letters.

Each element’s atomic symbol is an abbreviation of that element’s name. The first element listed on the table is hydrogen, which is “H”. If you find “oxygen” on the periodic table, you will see its Atomic Symbol is “O”.

But then why is potassium “K”? It starts with a “P”!

• Atomic symbols are sometimes abbreviations of a chemical’s Latin name. In the case of potassium, the “K” comes from “kalium”, the Mediaeval Latin word for potassium.
• Atomic symbols are sometimes taken from older names that aren’t used any more for a particular element, that were more common when the element was first put on the table. Silver has an atomic symbol Ag, which comes from argentum.

What Is the Atomic Number?
Remember earlier when we said atoms are made of different sub-atomic particles?

The three main particles to be aware of are protons, neutrons, and electrons.

Protons and neutrons form the nucleus of an atom — kind of like its body. The electrons float around the nucleus in what’s called the electron shell.

The atomic number of an element is how many protons are in the nucleus. Generally speaking, there are an equal number of protons and neutrons.

Hydrogen, with an atomic weight of 1, can actually be a single proton with no neutrons or electrons.

Oxygen has 8 protons, and so has an atomic number of 8.

You can split an atom to make elements of smaller atomic numbers, or smash atoms together to form elements with higher numbers. Doing either results in a lot of energy being released very quickly, often in the form of an atomic explosion.

What is the Atomic Weight?
This number usually sits at the bottom of the element cell, and is usually given to three or so decimal places.

This one is easy — it’s just how much the atom weighs! The unit of weight used for an atom is called a dalton. The weight given on a periodic table is quite precise, which is why there are usually a few decimal places in the number rather than a nice round even number.

How Are Elements Arranged on the Periodic Table?
Elements are arranged in a number of ways. Because the table is meant to group elements together in specific relations, it takes on a bit of a funny shape.

Firstly, the elements are ordered from lowest to highest atomic number, starting with hydrogen (1) in the top left. Elements are ordered left to right in atomic number by row.

But why is the second element, helium, all the way on the other side of the chart?

The 7 rows and 18 columns of the periodic table are used to arrange elements according to two properties:

• Rows represent the atomic period
• Columns represent families

What Is an Atomic Period?
Earlier we mentioned that electrons, one of the sub-atomic particles, float around the nucleus of an atomic in what are called shells.

Electron shells have layers, and each layer can only hold so many electrons.

Generally speaking, the larger the atom, the more electrons it has. As each layer of the shell gets filled up, the electrons start to fill the one above, and so on.

The atomic period is how many of those layers an atom can fit electrons into. Elements on the bottom layer of the periodic table can fit electrons into seven layers, elements on the top can only fit them into the first layer.

What Are the Atomic Families?
The columns in periodic table indicate how “full” the outermost layer of each atom’s electron shell is. Elements in the first column aren’t very full at all, while elements in the 18th column have “complete” shells.

What this tells us about each element is how reactive they are with other elements. Atoms form molecules by interlocking their electron shells. If the outer shell is mostly empty, the atom is very reactive. If the outer layer is full, it’s almost completely non-reactive.

What Are the Colours Used on the Periodic Table of Elements?
Colours on the periodic table are used to group atoms by element type. The exact colours use depend on whoever is designing the table.

So, for example, helium, neon, argon, krypton, xenon and radon are “noble gases”, elements which are very un-reactive (which you can tell because they’re in the 18th column, as explained above!) They will always be coloured the same.

The types elements get grouped into are:

• Alkali metals
• Alkaline earth metals
• Lanthanides
• Actinides
• Transition metals
• Post-transition metals
• Metalloids
• Other nonmetals
• Halogens
• Noble gases
• Unknown

Using the Periodic Table
So! Bringing it all together, looking at the periodic table can tell you a lot of information even without needing to read it in detail.

• Colours group specific types of elements together.
• Elements on the left of the table are more reactive than elements on the right.
• Elements at the top of the table have fewer electron shell layers than those at the bottom.
• The further along the element on the table, the higher its atomic number and atomic weight.

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