Karen Bacon answered on 11 Nov 2013:
That’s a tricky question for a biologist, but I’ll give it a shot.
Atoms are the basic unit of matter and the idea that matter had some basic unit has been around for a long time. The Ancient Greeks thought that all matter was made of some mixture of “elements” by which they meant air, water, fire and earth. It wasn’t until much later that experiments started to reveal the nature of matter and the details of atoms. Atom means “indivisible” and although we now know that atoms can be divided further into what are called “sub-atomic particles”, some of which are studied at Cern (which has been in the news lots because of the Large Hadron Collider), the term is still kept.
When the science of chemistry developed in the 1700s, elements were defined as a type of substance that could not be broken down any further by means of chemistry – think about water, which is made up of two hydrogen atoms and one oxygen atom. You can break a water molecule apart with lots (a surprising amount) of energy. You can’t break the oxygen molecule or a hydrogen molecule apart using simple chemistry though (as far as I know!). Many centuries of experiment have supported the theory of atoms and a British scientist called John Dalton first proposed that all elements consist of a unique type of atom that can be joined together to form compounds. Earlier this year, some scientists from the Netherlands successfully captured an image of a hydrogen atom that showed the nucleus and electron cloud orbiting it. I think this is one of the most extraordinary images in modern science. If you google “hydrogen atom image” you can see it.
That’s a very rough answer – a physicist would give you a much better one, but that’s a bit of what I understand of atoms!
Thomas Doherty-Bone answered on 12 Nov 2013:
To augment Karen’s detailed answer:
It started as an idea, an hypothesis. This was rigorously tested through many different experiments, looking at things in many different ways. The evidence supported the hypothesis that atoms existed, but rejected the hypothesis that they were the smallest possible things. They found things such as nuclei in atoms (found out by Rutherford in Manchester Uni firing lazers at a sheet of gold).
That all said, even though we have a nice visual model of the atom, physicists will still tell you that isn’t how it is based on evidence that does not support it. It is perhaps more a “working hypothesis” with new science challenging this.
Cassandra Raby answered on 14 Nov 2013:
Great answers by these guys, so I guess I’ll just sum it up a little.
The fact that things are made up of atoms is called the ‘Atomic theory’.
We have thought that everything is made up of small particles since Ancient Greece. This was done by ‘observations’ (just by looking).
And then later came the ‘experiments’ that Karen and Tom describe. This is when the scientists decide to test everything out to see if it supports their observations.
So a number of experiments were done. At first they thought an atom looked like a ‘plum pudding’, but then more experiments were done to find something different. As those guys have already told you, they basically fired particles at a sheet of gold, but the particles all bounced back in a different way – and some just went straight through! How could a particle go through a plum pudding?!!
That’s when the experiment showed that actually atoms are mostly empty space!
Sofia Franco answered on 19 Nov 2013:
Well, I guess your question has been covered 😉 check out this Discovery channel video if you want to know a little bit more about it!