Questions on Atoms (based on from reading some of "Atoms in Motion" - Chapter 1 - Feynman Lectures)

[studiot]

 

swansont

I was always taught that noble gases don't form molecules. I wonder if there is a geographic dependence on the definitions used here.

 

 

I expect that was a simplification imposed by your teacher.

 

 

What did she have to say about Helium and Avogadro's Hypothesis?

 

 

Historically the concept of atoms was introduced followed by the concept of elements and finally the concept of compounds.

 

Three laws were enunciated

 

The law of Definite Proportions

The Law of Constant Composition

The Law of Multiple Proportions

 

These codified the idea of 'pure substances' that could be formed from or reduced to simpler forms of matter (called elements), which could not be reduced further.

 

The natural question arose "If an atom is the basic form of an element, what is the basic form of a pure substance?"

 

This lead to the idea of a molecule, after quite a few false trails and some obstruction by some older scientists, lead by Berzelius.

 

The concept of a bottle or bag of a pure substance containing multiple instances of identical units is simple and alluring and offers a working explanation for many physical observation.

 

But it is only a model and not always reliable.

 

For instance what does a molecule of pure diamond look like?

 

 

tylers100

Last few questions before I move on to other lectures and / or topics:

 

If you are still reading this rather than moving on I was going to discuss your view of the space between atoms with some hopefully helpful comments.

 

Are you still interested?

Edited March 20, 2015 by studiot

[tylers100]

Studiot: Yes, I'm still interested.

 

It's just that I thought there are certain aspects of atom such as subatomic particles and elementary particles to be maybe bit too advanced or beyond my understanding for time being, that's why I mentioned that line (last few questions before moving on to other lectures or topics). But then I started reading this website: The Particle Adventure it seems to be interesting and useful, but however I'm not completely sure whether if it is credible or not.. let me know if it is or not, I don't want to blindly learn and understand wrong things.

 

Anyway, about the space between atoms... sure, as I'm still thinking about that.

[studiot]

 

Anyway, about the space between atoms... sure, as I'm still thinking about that.

 

 

My comment about atoms and molecules was meant to be a helpful simplification (particularly as you will meet technical terms as your reading progresses)

 

So I am interested in what you made of it.

 

 

As to space.

 

Think carefully what how you mentally picture an atom (from a distance, lets leave the inside till later)

 

You must have seen the 'ball and stick' models of molecules (there you go, a technical term) made of coloured balls to represent the atoms making up a mlecule and the sticks to connect them.

 

So when they are close enough to be joined together there are 'connection sticks' in the space between the atoms.

 

These are not solid or other atoms so how do they work?

 

 

Well instead of picturing the atom as a solid ball, think of a mist or fog.

 

As you walk through the mist some patches seem thicker, more dense than others.

The more tenuous parts may even thin out to clear air.

Furthermore if you walk far enough you will exit the fog and enter clear air.

 

Now think of an atom as being a clump of particularly dense fog but thinning out towards its edges, and think of two such clumps coming close together.

 

As they appraoch each other the thin edges will touch first, forming a thicker zone between the two clumps.

 

This thicker zone corresponds to the sticks in the ball and stick model.

It is formed by overlap of two fuzzy edges of the atoms.

 

How are we doing so far?

[tylers100]

studiot: I drew a picture. See below. Do the picture match your conceptual description of atoms? I drew two different groups of atoms as clumps of dense fog (1st located top and 2nd located below on the picture); I was unsure about the first one...it could be inaccurate representation of your conceptual description, so I drew second group.

[Sensei]

I was always taught that noble gases don't form molecules.

That had to be before 1962..

http://en.wikipedia.org/wiki/Noble_gas_compound

[studiot]

It is more like the second one, but you have the general idea.

 

This does not mean the ball and stick model is wrong or redundant.

That model is useful for other purposes.

 

Real world molcules are more complicated and unlikely to be symmetric.

Many are three dimensional.

 

This fog approach is called the charge cloud representation. Here are the charge cloud representations for oxygen and methane.

Compare the ball and stick with the CC for methane.

 

 

[tylers100]

studiot: Yes, on the 2nd picture.. I can see the difference between two representations of methane; the charge cloud on left is 3-dimensional and "ball and stick" on right is 2-dimensional. (the 2-dimensional representation.. is it called valence structure.. or Lewis structure? reference link: Lewis Structure)

[studiot]

No the methane pics both represent a 3D picture.

 

Pretend the carbon atom labelled C is a blue ball and the hydrogen atoms, labelled H are red balls and the tapered lines are sticks.

Then you have a ball and stick model.

 

I did say to ignore what was inside the atoms and neither of my pics attempt to show the details of the connections in the way the Lewis representations do.

 

None of these are Lewis representations.

 

To understand these would mean going into the structure of the atom and considering some sub atomic 'particles', we call nucleons and electrons.

 

The Wiki article shows some 3D structural (ball and stick) models at the top which is misleading because these are not the Lewis representation.

 

A Lewis example of this appears about halfway down the page with two images of the nitrite ion.

Lewis examples are all flattened to 2 dimensions and are used to show the nature of the chemical bonds involved, as well as the electrons not involved in the bonding process.

 

They are, of course, an example of a different model appropriate for a different purpose.

 

We have been talking about structure which, loosly speaking, is about the distribution of things in space and to a lesser extent what is directly connected to what.

[Sensei]

tylers, I recommend you getting ball-and-stick model f.e.
http://www.ebay.com/itm/Scientific-Inorganic-Organic-Chemistry-Atom-Molecular-Models-Links-Set-GFY-/381171962175?pt=LH_DefaultDomain_0&hash=item58bf9e913f

Mine model. 245 atoms in package.

[tylers100]

studiot: Very helpful comments.

Sensei: Good idea.

Questions and Comments on Atoms in Relation to Causality and Time:

In general, an energy or energies cause a motion of sort in atom? (I'm sure it "depends" on whatever.. but I'm being very general.)

If energy or energies does in fact cause a motion of sort in each atom, and make things happen... then what exactly is time.. in absolute sense?

To me, it seems that an energy or energies in atoms make things happen, not time.

If time doesn't exist, and it is actually energy or energies that make atoms move/interactions/etc. Then... the time as spacetime or 4-D doesn't exist?

Seems the energies... should be the one that define other dimensions? Energies as 1st dimension while the rest (2nd,3rd, and 4th) are spatial dimensions (ie xyz or width, height, and depth)?

And it also seems that causality might be the only one conceivable way to make 4-D universe.

I'm sure the questions and comments above might sound stupid or baffling or something like that, but these make sense in my mind somehow (at this moment so far).

[studiot]

Chicken and egg?

 

Force causes change of motion, including motion in the first place from still or rest.

As a result of motion a material body possesses energy.

Since we can distinguish several sorts of motion we distinguish several sorts of energy.

 

When a force causes motion it does work on the body, which means energy is transferred to that body from either another body or another store of energy.

 

Another store of energy?

There are non material places to store energy eg electric and magnetic fields.

 

It is true that we can plot other quantities than position along an axis on a graph, and that energy is a possibility.

 

Equally clearly when we draw such graphs the axis can be called a dimension and that quantity has a coordinate value relative to its axis.

 

We call these generalised coordinates.

 

In theory we could plot one for every conceivable quantity, but

 

because we can also deduce equations connecting at least some of the quantities we only need to plot some and can obtain the others form the equations.

 

The business of Physics is about finding the minimum number of such axes.

 

We tend to group together suitable and like quantities for example the familiar xyz axes, but there is no justification for calling any one the first or fundamental.

Edited March 21, 2015 by studiot

[tylers100]

studiot: Reduce axes (eg dimensions) to minimum number.. So very simple.. Almost like Occam's razor or reductionism approach, but of course only so far as evidences are concerned, right? One of other quantities along on an axis; is possibly energy.. Could you please elaborate on that more if you don't mind?

[studiot]

 

studiot: Reduce axes (eg dimensions) to minimum number.. So very simple.. Almost like Occam's razor or reductionism approach, but of course only so far as evidences are concerned, right?

 

The cynic would say that pure laziness has more to do with it than Occam. Why calculate three things when you only need to work out two?

 

Anyway let us use the xyz coordinates as an example.

 

Let us think of a particle free to roam the galaxy.

It can have any x or y or z coordinate quite independently of the other two.

We say it has three degrees of freedom.

 

Now let us restrict the particle to the surface of the planet Zog.

 

Zog is perfectly spherical with radius R and the centre of Zog is the centre of the galaxy.

 

So all points on the surface of Zog obey the equation x² + y² + z² = R²

 

Now all of a sudden if we know x and y we automatically know z.

 

We have reduced the degrees of freedom from 3 to 2 by introducing one equation or condition.

 

Now you asked about energy

 

Could you please elaborate on that more if you don't mind?

 

 

 

Remember I said that we distinguish several types of energy.

 

There is no better place to make such a distinction than in Thermodynamics.

 

Here our variables are quantities like, pressure, volume, temperature and yes energy.

 

In fact we have several types of internal energy, Helmholtz free energy, Gibbs free energy, work energy, heat energy, and so on.

 

I mentioned Gibbs and he put forward a formulation of thermodynamics, we call the Gibbs formulation and which Plank later called the canonical equations.

 

Maxwell was so impressed that he made a plaster cast of the graph of the Gibbs formulation and presented it to Gibbs.

 

These days we have CGI to draw such things for us on the screen.

 

However this is a webforum, not a textbook, so I will stop there.

[tylers100]

studiot: Thank you for explaining things in sort of explicit way.. I appreciate that.