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The Periodic Table

Part of Chemistry Creations

Today, we are exploring something that is used lots and lots when talking about chemistry – the Periodic Table – or to give it its full name: The Periodic Table of Elements.

You might recognize the shape of the table from the picture below (the design of the table gets put on all sorts of items like lunchboxes, shower curtains, coffee mugs).

But what is it?

The Periodic Table is a summary of all the chemical elements that make up the world – the building blocks of chemistry. For more of an introduction check out this video from Matt, featuring the huge Periodic Table we have in the Dundee Science Centre Café.

Periodic Table

There are lots of ways you can use the Periodic Table – it contains a lot of information – in fact some ways of showing the table have lots of detail included, like this version here.

Periodic Table
Periodic Table (Select Image For Larger View)

Things that can be included in a copy of the Periodic Table:

Name and Symbol: The most important things to include are the name or the element or its symbol. Take oxygen for example – the symbol is O (which makes a lot of sense) - or for iron the symbol is Fe. The symbols make it easier to talk about combining elements into compounds.

Group Number: this is a way of labelling the columns of the table – columns of elements tend to have similar properties. The left-most column, called Group 1 is made up mostly of reactive metals (with the exception of hydrogen). The right-most column, sometimes called Group 0, is made up of the “Noble Gases” – gases like helium or neon that react with almost no other chemicals.

Period Number: this is a way of labelling the rows (or “Periods”) of the table.

Atomic Number: the element’s atoms have a particular structure, made up of a nucleus at the centre and electrons orbiting around it. The nucleus is made up of two kinds of particle: protons and neutrons – the atomic number tells you how many protons are in the nucleus – for hydrogen it is 1, for carbon it’s 12, and for uranium it’s 92. The atomic number actually forms the definition of an element – a pure substance made of atoms with a fixed atomic number.

Atomic Mass: this is another property of the atomic structure. It’s the total number of protons and neutrons together in the nucleus – and can vary from atom to atom of an element. For example chlorine atoms all have 17 protons in the nucleus, but there can be either 18 or 20 neutrons (and very rarely 19). On average the atomic mass comes out as 35.45, which is somewhere in between! The heaviest natural element is uranium with an average atomic mass 238.03 (Note: the mass of the electrons hardly counts at all to the mass of the atom – an electron is over 1,800 times lighter than a proton or neutron, which have masses roughly the same).

And more! Some tables include things like the melting point and boiling point of the element, or are colour coded to show which elements are solids, liquids, or gases at room temperature.

But chemistry doesn’t stop at elements! You can combine elements in many different way to make what we call “compounds”. For example:

Water: has a chemical formula of H20 – meaning there are two hydrogen atoms and one oxygen atom in each molecule of water.

Carbon Dioxide: has a chemical formula of CO2 – meaning there is one carbon atom and two oxygen atoms in each molecule of carbon dioxide.

Table Salt: has a chemical formula of NaCl – meaning that for every atom of sodium there is one atom of chlorine.

But say you don’t know the chemical formula of your compound? How do you figure it out? Well, one starting point is to look for tell-tale colours when your compound burns – as Matt demonstrates in this video.

Flame Test Video

Come back tomorrow where we’ll be exploring two very important types of chemicals – acids and alkalis!

Atomic Structure
Atomic Structure

This page is part of the Chemistry Creations information.

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