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I like to help people learn.

Modern experimental evidence supports the atomic model

For the last several posts, we’ve gone through the atomic nature of the physical world and the model of the atom.  Now let’s turn to modern evidence that these ideas are correct.  Remember, atoms are too small to see with the eye, even with the best microscope.  So how do we know the model is correct?

There is lots of evidence the picture is correct.  In most cases, there are layers of physics between the observation and the interpretation which is fine if you take the time to understand the physics.  Here I’ll talk about what is – in my opinion – the observations with the smallest amount of physics between what is measured and what we describe as seen.   Continue reading


Topic 5 – Atoms and Isotopes

Isotopes of lithium

Image from “Russell’s Blog” which you can access by clicking on the image

Last time we talked about the important parts of atoms – protons and electrons – and how they come together to define the unique properties of every element.  Now let’s tackle the one remaining part, which is how neutrons fit into the mix.  Remember, neutrons and protons are practically the same thing in terms of mass, except the proton carries a positive charge.  The neutron even says it in the name.  It is neutral, meaning no charge, just mass.

That mass is what the neutron brings to an atom.  The mass of an atom is dictated by the number of protons and neutrons.  The identity of an atom is defined by the number of protons, so a given element will always have the same number of protons.  Lithium always has three protons, carbon has six protons, iron has 26 and so on.  The number of protons is so important, it is called the atomic number and you will find it on every periodic table you will see.   Continue reading

Topic 4 – The atom: Putting it all together


In the last few posts, the atomic nature of the universe was discussed, Dalton’s atomic theory explained and we took a tour of the “guts” of an atom.  Now let’s use all this to understand how the pieces fit together to illustrate what makes the element (and atom) hydrogen, different from carbon, oxygen and neodymium.  The short story is the way the parts come together – it’s really a counting game.


This links to a periodic table you can download.

A new element is discovered almost every year – but for now, a current periodic table will show 118 unique elements.  (I’ve linked this image to a good table you can print out if you wish.)   All periodic tables will have at least 3 pieces of information.  For each element, every table should give you at least the symbol, the atomic mass and the atomic number.  Some have far too much information, stuff you should be able to infer from the position on the table, they symbol, the mass, and so on, but every table – except the ones on the shoes at the top of this post – should give the three fundamental data.  Of these three, the most important is the atomic number.  So important is the atomic number, notice it provides the organizing principle for the arrangement of the atoms.   Continue reading

Topic 3 – What’s an atom made of, Dad?

My poor parents – especially my Dad.  When I was young, I never stopped asking questions.  I was like David After Dentist but I never sobered up and quit.  Eventually, my Dad started acting like he was hard of hearing, but oddly, only when it was just the two of us.  I often wonder if this isn’t a reason why so few kids end up in science – it can be very hard to encourage constant questioning and that’s one of the most important qualities of a scientist.  Today, let’s ask about the “guts of an atom.”

Representation of protons, neutrons and electrons

Protons, neutrons and electrons scaled to a pool table. Think of the neutron as a cue ball, the proton as an eight ball and the electrons are tiny BBs.

Last post was about Dalton’s Atomic Theory, and before that, about the atomic nature of the physical universe.  Now it’s time to drill down into the atom.  I’m going to talk about this from the perspective of a chemist – which limits us to only three basic parts: the proton, the electron and the neutron.  Each of those parts is made up of even more fundamental bits – quarks, charms, strings, and on and on.  The dividing line is one based on energy.  Super high energies – far greater than those one can obtain even at the center of a hot, hot sun – are necessary for the proton, neutron and electron to be broken into the pieces studied by high-energy physics.  That’s the world the guys on “The Big Bang Theory” live in – they use super powerful machines to create those high energies but a chemist works in the world of every day heat and energy.   Continue reading

Topic 2 – Dalton’s Atomic Theory

The Evolution of the Atom

This shows the evolution of the model of the atom. It begins at top left with Dalton’s idea of an indivisible particle and moves to the left until Bohr’s model appears in the lower left. Bottom right is a modern representation.

Last time, I introduced the atomic nature of the physical universe. This time we will look a little deeper at its roots.

The history of chemistry goes back thousands of years, probably starting with the alchemists, and it’s interesting. The alchemists might be among the greatest con men of all time. That period in the development of science is a great story for another time.

When thinking about atoms, we start much later in history, with the work of John Dalton who contributed the major portion of his work around 1800. His model of the structure of matter marks the beginning of modern chemistry and while today, we know he missed the mark on a couple of his assertions, his basic model still serves as a simple way to understand much of the physical universe. Continue reading

Topic 1 – The Atomic Nature of the Physical Universe

An atom with its orbitals showingIf you take a moment to look around you, it’s a gorgeous world.  Every single thing you see that is solid has a shape, and the liquids and gases swirl and wave in ways that are wonderful to watch.  The macroscopic world is not only beautiful but it is functional.  The shapes, sizes and colors have function and meaning and in most cases, purpose.

But even the young school children know something like a tree is not one solid piece.  There are at the very least, bark, leaves and branches.  Right now if you look around wherever you are, you will probably easily notice that most things are made of pieces.  As I write, I am at my desk and in front of me I see pens, my computer screens and a couple of speakers.  The pens have caps and clips and I know inside I will find a thin pipe and inside that I will find ink.  The screens have a variety of plastic pieces all with different purpose and I know there are circuit boards and wires inside.  The speaker has a variety of buttons and knobs and the different kinds of materials are obvious.  Without really thinking about it, we see a pen, a screen and a speaker – the whole – but upon closer inspection, most things can be decomposed into parts.   Continue reading