1.2a Atoms and elements

Atoms and elements are words known to many but understood by few.  They crop up in discussions everywhere from medical treatments and aircraft manufacturing to the depths of outer space. The difficulty many of us have is distinguishing between the two and grasping what each word really means. Is water an element, for example (as the ancient Greeks thought)? Is oxygen or carbon dioxide or plutonium? Is an atom the same as an element, or smaller or larger than one?  What exactly is an atom, anyway, and what does it look like?

It’s not hard to grasp the difference and it clears up a lot of confusion if you do. Both words concern the variety of the substance of which the world is made. Since the ancient Greeks, at least, thinkers such as Leucippus and Democritus have pondered this question, so you’re in good company. Some, such as Thales, imagined everything to be made ultimately of a single type of substance – like water, for instance, which is normally a liquid, yet can evaporate into air (or freeze solid). With the 18th century Enlightenment, however, these questions began to be pursued more definitively, through systematic experiments rather than pure speculative reasoning.

The basic question we all ask at some point is “what do you end up with when you break things down repeatedly?” Is there one fundamental building block or are there many? As one person once put it colourfully in a discussion: “when a daisy dies, what is left over – it can’t just be daisy atoms?” The answer, it turns out, is slightly more complicated than you’d hope. But one thing is very clear: you don’t have different building blocks for each separate thing – no daisy atoms, grass atoms, cement atoms or wood atoms. There are much fewer types than that.

metal grains

If you were able to break down different kinds of substance you’d see they are all made up differently at first. Wood for example, is made of fibres as we can know from paper-making, metals when greatly magnified are made up of tiny grains (as in the diagram) ………human cells….. and living tissue is composed of microscopic cells.

All this was revealed after the invention of the microscope which enabled small structures, invisible to the naked eye, to be seen. It turns out many substances are structured at several levels. For example, the cells of living tissue are themselves a composition of walls (called membranes) and internal structures, like the mitochondrion and nucleus.

But the fundamental thing people really want to know is what are things made of at the lowest level: what the cells in a living thing are made of, what’s beneath the fibre in wood and the grains in metal. Is there a fundamental thing that can’t be divided up any more, as the ancient Greeks expected when they coined the word atom? Thanks to the meticulous work of chemists in the eighteenth and nineteenth centuries and the physicists that followed them, we know a lot about this now and it turns out to be interesting and not as straightforward as expected.

The first thing to became clear concerned the nature of different substances. Later, the structure of them became clearer too. It was gradually revealed that some substances you encounter are just themselves under all conditions and can’t be broken down into more fundamental substances. Gold is like this and iron and sulphur and carbon. As they cannot be broken down any further they are elemental and hence called ‘elements’. Most substances, however, are not like this – they are made from more than one element and are known as compounds for this reason.

There are over 90 different elements and they are beautifully displayed in the Periodic Table – that mystifying iconic chart adorning every school chemistry lab.

periodic tableEach element has different properties: looking and behaving differently. Some are metallic (like iron), some are powdery (like sulphur) and some are gases under normal conditions (like neon). They are, however similar to one another in their basic structure. And this is where we encounter the second key concept: the atom. This word denotes the fundamental structural unit of each element.

atomic structure - planetaryThe important point is that all atoms have the same overall architecture; they are tiny and round and are all made of the same fundamental components – various kinds of particle. What distinguishes the atom of one element from another – gold from carbon or sulphur, for example, is not the things of which they are made, but how many of these particles there are and how they are arranged.

It’s quite possible that this news about atoms is more confusing than you’d expect and maybe even a little disappointing. After all, the idea of atoms – ever since the ancient Greeks first conceived of them – was that they are indivisible, they are supposed to be the ultimate, unbreakable foundation of all things. The truth, arrived at somewhat surprisingly in the nineteenth century, is that even atoms are made of smaller things; they too can be broken up into smaller pieces. The word ‘particle’ had to be introduced for the parts of which an atom is composed. It’s the very breaking up of atoms and release of the particles of which it is made that give rise what we know today as radioactivity, nuclear power and the cause of the Sun’s apparently boundless energy. More about these fascinating topics in later blogs.

Now we have clarified the difference between elements and atoms, we’ve made a giant step forward in grappling with science. Atoms of various elements make up everything we know (almost) and help us understand all matter – from bricks and mortar to flesh and bones. One further complication lies ahead, however; an unexpected complication that baffled the early chemists of the 18th century. Their meticulous experiments kept suggesting that when elements combined together in reactions, like coal (carbon) burning in air (oxygen), they didn’t seem to do so in the right proportions. It seems that the atoms of many of the substances we ordinarily come into contact with come in multiples. The building blocks of oxygen seem to weigh as much as two atoms for example, and water three atoms. Experimental evidence gradually showed that more than one atom was involved in the building blocks of many substances; for this kind of fundamental entity the name ‘molecule’ was invented. Today we know that most of the substances in the biological world are built of molecules: flesh, blood, leaves and oil. The same is true for the food we eat, the toothpaste we use and air we breathe. The ubiquitous ‘molecule’ is explained more fully in the next blog. By grasping the concept we can begin to explore how our bodies function, where energy comes from, the make-up of food, plastics and a host of other aspects of our lives.

If you found this interesting, you might like to look at 3. Fundamentals: molecules which takes the topic a little further.