Atomic and Molecular Scale

A scale explorer that fixes the nuclear radius at one, lays out the electron shells of all 118 elements and the sizes of molecules on that same ruler, and lets you see how much of an atom is empty space.

An atom is mostly nothing

Textbook diagrams draw the nucleus and the electrons at whatever size fits the page, which hides the real proportion badly. Here the nuclear radius is pinned at one and every shell is drawn as a multiple of it, so as the shells expand the nucleus shrinks to a single dot on screen. Stepping through all 118 elements also shows how shells are added and how atomic radius rises and falls across each period. The phrase "an atom is mostly empty space" stops being a slogan once you watch the ratio at true scale.

Choosing elements, switching to molecules

Pick an element and its shell structure is drawn immediately. Zoom with the wheel or a pinch to travel between the region right around the nucleus and the outermost shell, and drag to bring any part of the structure to the center. Molecule comparison lives in its own tab, so you can move from a single atom to structures built out of several without losing your place. Alternating between a light element and a heavy one is the quickest way to see what changes and what does not.

How the shell radii are computed

Shell radii come from the Bohr model with a Slater screening approximation. Inner electrons partially shield the nuclear charge, so an effective nuclear charge is derived first and each shell radius follows from it. Real atoms are probability clouds rather than tidy rings, so the crisp shells you see here are a device for conveying size, not a picture of where an electron is. The numbers are meant for teaching and orientation; reach for proper quantum chemistry results when precision matters.

Good moments to open it

In a chemistry lesson it replaces a table of radii with a picture of how atomic size shifts along a period and down a group. Once the nucleus-to-shell ratio is drawn honestly, the Rutherford scattering result becomes much easier to motivate: almost everything passes through because there is almost nothing there. The molecule tab extends the same ruler outward, so the step from one atom to bulk matter can be told as a continuous story. It runs in the browser with nothing to install and works on phones, so it is easy to pull up mid-class.

Look it up here

• How big is a hydrogen atom? A hydrogen atom has a radius of about 52.9 pm, or 0.53 angstrom, and carries just one electron shell. Show it here →
• How many electron shells does a carbon atom have? Carbon is element 6 and holds two electron shells, one layer more than hydrogen. Show it here →
• What does a gold atom look like? Gold is element 79 and stacks five electron shells, which makes it look far bulkier than carbon. Show it here →
• How much bigger is a molecule than an atom? The molecule tab puts molecules such as water and proteins on the same scale as a single atom for comparison. Show it here →

FAQ

Is an atom really almost entirely empty?

Nearly all of the mass sits in the nucleus, yet the nucleus is minuscule compared with the atom around it. Fixing the nuclear radius at one and drawing the shells, as this view does, makes that ratio visible. The space is not useless, though: the electron cloud fills it and keeps other atoms from simply passing through.

What are the shell radii based on?

They are computed from the Bohr model with a Slater screening approximation: shielding by inner electrons gives an effective nuclear charge, and each shell radius follows from that. Actual electrons are spread out as probability clouds rather than sitting on a line, so read the rings as an approximation of size.

Can I compare molecules as well?

Yes. Molecule size comparison has its own tab, so after looking at the shell structure of a single atom you can move straight over and see how molecules compare on the same scale.

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