Metalwork - Materials - Atomic Structure

Atoms... what are they? Well they're small, that's for sure, but they are so important ! Someone has said to you at some stage, 'dot your i's and cross your t's... it's not hard !'. Well every dot on an 'i' has aproximatly a million, million, million atoms in it, ... that's 1,000,000,000,000,000,000 atoms ! (Who bothered counting ?!) They are so small that they cannot be seen by the naked eye. It takes some very special equipment in order to prove that they exist. In ancient Greek philosophy the word 'atom' was used to describe the smallest piece of matter that could be concieved. It wasn't until the 1890's that major advances were made in the field of Atomic Theory when a man called J.J. Thomson discovered that the Atoms themselves could be broken into smaller parts. An Atom is now defined as the smallest part of an Element that retains the properties of the Element. Atoms are the building blocks that make up all matter.

What is an Atom made of ?

Again just to make sure that you know, an Atom is the smallest part of an Element that retains the properties of the Element. It was originally thought that an Atom could not be divided into smaller parts. Then around the 1890's, J.J. Thomson discovered Electrons and this led to more detailed studies on Atoms.

We will start by looking an a Hydrogen Atom, which you can see on the right. (Before anyone starts kicking up a fuss, this is just a simple representation of an Atom). An Atom is made up of two main parts, firstly the Nucleus, the red sphere you can see in the middle and secondly the Electron Cloud, which is the random path the Electron follows around the Atom.

It is interesting to note that most of an Atom is made up of empty space. Relatively speaking the distance between the Electron and the Nucleus is approximately the same as the distance between the Moon and the Earth. Remember I said 'relatively'.

The Nucleus, which you can see a diagram of, on the right, is made up of Protons which have a positive charge, and Neutrons which don't have a charge and so are neutral. As a result the Nucleus has a positive charge. The Protons and Neutrons are all bunched together in a tight ball. The diagram to the right is not the Hydrogen nucleus, as a Hydrogen Atom has only one Proton and no Neutrons. However all of the other Elements have both Protons and Neutrons. If you would like more information on Protons and Neutrons go first to the section lower down on Atomic Mass and then onto the Periodic Table of the Elements.

The Electrons occupy the space often referred to as the Electron Cloud. This is difficult to visualize, but the electrons don't ordit the Nucleus in a circular pattern, the whizz around the Nucleus of the Atom. Look again at the Hydrogen Atom at the top of this section... try and imagine a sphere the size of the circle you can see.... now in reality the electron could be anywhere inside that sphere. And so it's called an Electron Cloud. Simple, I hear you say, unfortuantly it's only simple in this case, because it's Hydrogen, but the principal is the same for other Elements. On the left you can see a diagram of another type of Electron Cloud that looks like a dounut with wings. Well it's not a dounut and they're not wings, it's just a differently shaped Electron Clouds. Different Atoms, depending on the number of Electrons they have, have Electron Clouds of different shapes. Even still Atomic scientists are not 100% sure where the Electrons will be. The diagram that you can see on the right is an approxiamtion based on a lot of test analysis. The good thing is that it's not necessary for you to know any more about this!

Electrons have a negative charge. The total charge of the Electrons in regular Atoms equals the total charge of the Protons, therefore a regular atom is neutral in charge. If you would like to know more about Atoms that do not have an equal number of Electrons and Protons you want to read about Chemical Bonding, where we look at Atoms that have lost or gained Electrons. It is now believed that there are even smaller parts called Quarks inside the Nucleus of the Atom, but technology is not yet sufficiently advanced to find this out for sure.

Electronic Configuration

Understanding the Electronic Configuration of Atoms is very helpfull when you wish to understand Chemical Bonding. The Electrons which whizz around the Nucleus of an Atom do not do so totally randomly. They fit into different levels which are called Shells, and only a limited number of Electrons are allowed in each Shell.

On the right you can see an Argon Atom. Each Shell is shown by a black circle, and as you can see from the diagram the first Shell is only allowed to have 2 Electrons.

The second and third Shells are both only allowed to have 8 Electrons each.Remember it is a very simple diagram and in reality the Atom does not look like this. The diagram makes explation much easier.

If you remember the diagram of the Hydrogen Atom near the top of the page, it had only one Electron and it was situated in the first Shell. It is important to remember that there is a limit on the number of Electrons in each Shell. When a Shell is full the Electrons move to the next outermost Shell.
The Electronic Configuration is written like this example for Argon : 2-8-8. The Electronic Configuration for Hydrogen is written simply as: 1. To see more examples of Electronic Configuration goto the Periodic Table Of The Elements.

Atomic Number

The Atomic Number of an Element gives us three pieces of information. Firstly it gives us the Elements position in Periodic Table Of The Elements. Secondly it gives us the number of Protons and thirdly the number of Electrons. If you remember we already said that there were an equal number of Protons and Electrons in every Atom.

We will take the Oxygen Atom as an example. Oxygen is in position 8 on The Periodic Table Of The Elements. Therefore it should have 8 Electrons and 8 Protons. Oxygen has an Electronic Configuration of 2-6, and this confirms that it has 8 Electrons.

Atomic Mass

Because Electrons, Protons and Neutrons are so small it would be impractical to measure their mass in normal units. As a result a scale unit called the Atomic Mass Unit or amu for short is used. This scale is based on the Carbon Atom which is taken to have an amu of 12. Electrons are much smaller then the Protons and Neutrons, (they have a mass of 1/1840 amu), therefore they are not taken into account when measuring the mass of an Atom. The mass of an Atom is the mass of the Protons plus the mass of the Neutrons, and both have a mass of 1 amu.

Atomic Mass = Mass of Protons + Mass of Neutrons

Using this information we can calculate the number of Neutrons in an Element. We will take Aluminium as an example. Aluminium is in position 13 in The Periodic Table Of The Elements. This information tells us that Aluminium has 13 Electrons and 13 Protons. From the Periodic Table we can also see that Aluminium has an Atomic Mass of 27 amu. Changing the above formulae slightly we get:

Mass of Neutrons = Atomic Mass - Mass of Protons

As each Proton has a mass of 1 amu all of the protons in Aluminium have a total mass of 13 amu, therefore :

Mass of Neutrons = 27 - 13

Mass of Neutrons = 14 amu

So now you should know as much as you need to know about Atoms for Metalwork. A good idea would be to give The Periodic Table Of The Elements a good looking at. You should be familiar with at least the first 20 Elements and it is always handy to know the metals... after all that's what you're here for !