The Bohr Model of the Atom

Lesson notes

Overview

Electrons orbit the nucleus in discrete shells. Change the proton count to build any element. This topic is rated beginner and is number 1 of 110 in Chemistry. Core ideas and first intuitions. No prior knowledge needed.

What you are seeing

The panel above shows an interactive animation of the idea. Every slider changes one quantity so you can see its effect on the outcome. The animation is drawn live from the model, so everything you see responds to the sliders. Press Space to pause, use Restart to replay from the start, and change the speed to slow down quick events.

In depth

In Bohr’s model, electrons orbit the nucleus in fixed shells, each with a definite energy, and a shell number n can hold at most 2n² electrons: 2, 8, 18, and so on. An electron absorbs or emits a photon only when it jumps between shells, which explains line spectra. The number of protons, the atomic number Z, defines the element, and a neutral atom has the same number of electrons. The model is a simplification of quantum mechanics, but it remains a useful way to picture electron arrangements.

The key idea, step by step

1. Electrons orbit the nucleus in discrete shells. 2. Change the proton count to build any element.

Reading the relationship

The expression "shell capacity = 2n²" is a compact summary of the idea. It uses the symbols s, h, e, l, c, a; name what each one stands for before you start. Notice that it contains a squared term, so doubling that quantity changes the result by a factor of four. Then use the sliders to see how changing one quantity changes the others.

A guided exploration

1. Run the animation once with the default settings and describe in words what happens. 2. Change one slider at a time and note which quantity responds most. 3. Push each slider to its extreme and decide whether the result still makes sense.

Try this

Start by only moving one slider at a time. Say aloud what you expect, then check.

Common pitfalls

Keep the particle picture in mind. Mistakes often come from treating a rate, an amount and an equilibrium position as the same thing, or from ignoring units and conditions.

How it connects

Once you are comfortable, continue with “Hydrogen, the Simplest Atom”.

Why it matters

Chemistry links the tiny scale of atoms to the materials, medicines and energy we use every day.