What are atoms?

Here is a question I was asked at a job interview not too long ago.

'Explain what atoms are in simple terms'

Despite a degree in physics, I made a dog's dinner of this & gave some rubbish about really really small things.

I was thinking about it recently and looked up a definition & found:

atom: the smallest particle of matter which can partake in chemical reactions.

Sounds straight forward. But then I thought, what is a chemical reaction? Isn't it just an interaction between atoms (and collections of atoms). But that's recursive isn't it?

Any suggestions for answers?

How about considering that atoms are "unbound", i.e. no sharing of electrons with other nuclei. No sharing at all, for that matter.

(Sorry, but a couple of things have been discovered since I studied chemistry back in the Stone Age. :) )

-Skipper

I had to think about this a bit too hard, being a chemistry undergrad I should know a proper defination. An atom I suppose can be defined of as a collection of protons and neutrons ( doesn't have to have neutrons, H ), orbited by a number of electrons equal to the number of protons.

A chemical reaction doesn't have to involve more than one atom. Lots of things happen to just single atoms ( unimolecular reactions ).

>How about considering that atoms are "unbound",

Oh. OK then I'll have a go...

'The smallest particle of matter, which is made up of even smaller particles'. (No that's rubbish.)

Erm...

'The smallest piece of stuff which you can cut with a really sharp knife'. (No that's not good either.)

'The smallest pieces of solid stuff possible.' (Oh dear.)

'The smallest things you can see with a really good microscope'. (Getting worse).

Of course, I could just go & look it up in a proper physics dictionary. But that would be too easy.

So how about...

'Atoms are systems which represent an arbitrary layer in a scale from the infinitesimal to the infinite.'

Things were so much easier before those damm quarks came along. It would have been:
"The smallest division of matter"

>Things were so much easier before those damm quarks came along

Not really. Things like electrons, protons, neutrons were known about for along time before quarks.

Doh!
[note to self]
think before typing
[/note to self]

Good job my lecturers arn't reading.

On thinking though I don't think I did too bad

Quote:

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a collection of protons and neutrons ( doesn't have to have neutrons, H ), orbited by a number of electrons equal to the number of protons.

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An atom doesn't have to have an equal number of electrons. It can have fewer, in which case it's a positively charged ion, but still an atom.
How about a self contained system consisting of at at least one proton, optionally bound with neutrons and optionally orbited by electrons, that makes up the smallest division of a distinct chemical element?

Told you...

Quarks weren't invented when I went to school. Heck, the fuse was still burning on the "Big Bang". :D

-Skipper

Rolls up sleeve and points to arm..."This is an atom, can't you see it?"

Thats the answer I like

Salvelinus,

But...an ion - can be - an atom that has gained, or lost, an electron constituting, I believe, a chemical reaction.

I'll defer...(since you live in the right state. :))

(Love to hang around, but I'm going bowling with my wife and gonna suck some beers. (Have a pint...or six...for our non-American friends.) I'm a whole lot better at one than I am at the other. Your guess. ;) )

-Skipper

atom= An atom is a particle of matter that uniquely defines a chemical element. An atom consists of a central nucleus that is usually surrounded by one or more electrons. Each electron is negatively charged. The nucleus is positively charged, and contains one or more relatively heavy particles known as protons and neutrons.

chemical reaction= a collisions between two particles at the correct angle and at the correct momentum resulting in the fulfilment of the activation energy. This is then followed by an chemical bond.

>chemical reaction= a collisions between two particles

That is a very classical understanding!

How about "the smallest division of any given element"? That's what I'd say.

But nuclear fission isn't a chemical reaction?

The problem with all these descriptions is that they don't offer any insight or real understanding.

Describing atoms as a package of protons neutrons etc. is like defining water as a colourless, ouderless, tasteless liquid. While it may serve some purposes, it doesn't provide a deeper understanding of what water actually is.

So what's the difference between an electron and an atom? Why do we perceive collections of atoms as solid & electricity as not?

>>The problem with all these descriptions is that they don't offer any insight or real understanding.<<

This is because of the arbitrary nature of the core definitions/assumptions within science as a whole and the jargon inherited by it from older systems of thought.

'Atom' simply means 'indivisible' (I think Democritus is credited with the notion and word: atomos). For science 'indivisible' is just great for classical/pre-20th century physics, but is not so good for 20th/21st century science because radioactivity blows a hole (sometimes literally) in the concept of 'indivisible', not to mention the reality smearing of quantum theory (ie topography/geometry of energy levels whether of nuclear or atomic material is described in terms of probability - there is no absolute boundary between what 19th Century science would have considered as absolute and separate chunks of matter: atoms).

So you're back to a dynamic and arbitrary definition again - because it changes to suit the paradigm/belief of the moment.

With regard to you job interview, presuming it was for a scientific position, it would be wise to stick to a 'standard' or current definition along the lines of the smallest unit of matter/energy that can participate in chemical reactions. Better still, play the game of rhetoric and point out that it can have a variety of meanings and throw the question back. If the interviewer fails to appreciate the possible meanings of his/her question then it's probably a good point to wish them every success in finding someone who is suitable for the job as you are, unfortunately for them, far too knowledgeable to waste any more of your valuable time in their Company. ;)

Note: Chemistry may be regarded and is sometimes described as, 'Atomic' physics, dealing as it does almost exclusively with the electromagnetic force (radiochemistry aside) - photons and electrons; neutrons and protons (nuclei) are just chunky bits that provides a convenient descriptor for mass and a useful balancing act for electronic charge.

I like CShot's answer the best, though. :D

Code:

---

class Electron
{
};

class Proton
{
};

class Neutron
{
};

class Atom
{
  Proton* pptr;
  Electron* eptr;
  Neutron* nptr;
};

class Molecule
{
  Atom* aptr;
};

---

Funny Onion!

:)

Ken Fitlike isn't too far wrong. I'm doing my chemistry degree now and the nucleus could just be a dot as far as I'm concerned ( organic chemistry aside ). I can however tell you all about the lovely shapes of probabalistic electron density clouds. My first lecture course was on quantum mechanics.
"Chemistry is based around the electron, therefore to understand chemistry you must understand the electron".

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Originally posted by Nick
But nuclear fission isn't a chemical reaction?

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that would be a nuclear reaction

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Why do we perceive collections of atoms as solid & electricity as not?

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that would be because electricity is the motion of electrons from one atom to the next think of it as a fire squad where every atom passes on the electron to the next one...

An atom is simply a catagorization describing groupings of smaller particles. Interestingly, there are not 3 but 2 of these smaller particles! The neutron split yeilds a proton, an electron, and a photon! In turn, the electron may simply be a 'bound' photon, and if all of the above are correct, then the true 'particles' are reduced to protons and photons(quanta of light).
As far as chemistry is concerned, reactions cannot make any changes to the nucleic structure of the atoms involved. That is, when you burn somthing, nothing changes on the atomic level, merely on the molecular (aside from stripping electrons). However, if too many proton/neutron pairs are grouped into a neucleus, the atom becomes unstable and splits into somewhat equal halves, resulting in a very sizable release of energy and some mass loss(fission). Alternately, if you superimpose nucleic matter, you can cause it to not merely split, but almost fully convert to energy(fusion). The most interesting fact about atoms is that they are mostly reused. We are literally made up of the mountains and rivers of the earth!
Also, with electricity, it is not that the electrons are passed along, rather, the vibrational intensity and frequency excite neighboring eloctrons to respond in kind to their neighbors. So I suppose with electrocution, you are actually shocking yourself to death :D

>>Ken Fitlike isn't too far wrong. <<

That's a relief. :D Sorry, for 'energy levels' read 'particle density distribution'. :)

>>I'm doing my chemistry degree now<<

I finished with chemistry so long ago that it was called 'alchemy' :p ;)

>>organic chemistry aside<<

nmr? If so, then covered by electromagnetic force.

>>I can however tell you all about the lovely shapes of probabalistic electron density clouds<<

Oooooh! You'll go far! It takes that something extra (in my opinion anyway) to get excited by orbital symmetry. Good luck with that degree! :D

>>As far as chemistry is concerned, reactions cannot make any changes to the nucleic structure of the atoms involved. <<

Radiochemistry? :p (Thus my description, "the electromagnetic force (radiochemistry aside)". Nuclear transitions involve weak (radioactive decay) and strong nuclear forces. )

Here's one for cold fusion, first proposed (late 1950s?) by Andrei Sakharov (USSR physicist and dissident): Take a couple of deuterons (heavy hydrogen), replace the electrons with mesons (negatively charged like electrons but more massive) and sit back and watch as the wonderfully wierd quantum world makes its presence known. Since all 'particles' exist in a superposition of states and that their 'density distribution' can only be measured in probability, the chances of two hydrogen nuclei in a diatomic hydrogen molecule ever being close enough together, at a moderate temperature, is vanishingly small. By replacing the electrons with mesons and bumping up the mass number of hydrogen to deuterium, the probability of nuclear fusion ie 'overlap' of the nuclei, while still very low, is realised.

>>fact about atoms is that they are mostly reused<<

...and is the original object orientated language (which Endo has already alluding to). ;) Is this why there seem to be a lot of proto-chemists/chemists/former chemists here at cprog?

If one considers an ion to be an atom, (I don't - an atom is uncharged a charged "atom" is an ion), and one accepts that an H+ ion is simply a proton, (i.e. a Hydrogen nucleus), and we accept that H+ ions can be involved in chemical reactions, and we say that a proton is smaller than any atom, then does it not follow that a nuclear particle, the proton, is the smallest particle that can take part in a chemical reaction?

Where the hell is Clyde when you need him?

Chemical reactions are per-force polaric. Therefore, the electron is the smallest participant in chemical reactions (and the most active initiator due to it's speed and freedom). The proton is almost 2000 times more massive than the electron, thus it is slow and heavy.

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I finished with chemistry so long ago that it was called 'alchemy'

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:D

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>>fact about atoms is that they are mostly reused<<

...and is the original object orientated language (which Endo has already alluding to). Is this why there seem to be a lot of proto-chemists/chemists/former chemists here at cprog?

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Nice analogy there.

>>H+ ion is simply a proton<<

Only in plasma. In solution the free proton doesn't exist (well maybe for an infinitesimal duration...), it's solvated eg in water as H3O+.

>>then does it not follow that a nuclear particle, the proton, is the smallest particle that can take part in a chemical reaction?<<

Already covered by "This is because of the arbitrary nature of the core definitions/assumptions" ie it is whatever you state it to be, provided all subsequent measurements and observations are made from that perspective.

But consider that this hypothetical free proton interacts with other matter: it abstracts an electron, or rather interacts to produce some other stable/meta-stable 'compound'. Which leads to:

>>the electron is the smallest participant in chemical reactions<<

Similar to the free proton but also can exist solvated eg in ammonia (NH2-) where it forms a beautiful blue colour.

For those looking for a standard/working definition, then definition 3a of this atom seems utilitarian enough. :)

I realise the H+ attaches to one of the lone pairs on the water Oxygen, however, the chain of reasoning came about when I read this from the thread...

>>> atom: the smallest particle of matter which can partake in chemical reactions.

...it struck me that this was not an adequate definition.

I think part of the problem with this thread/problem is that we are trying to fit todays understanding of matter into an old fashioned terminology framework - the foot is bigger than the shoe.