The Structure of Atoms

The atom is mostly vacuum, its mass concentrated in the neutron- and proton-filled nucleus. Quantum mechanics describes the strange behavior of matter at small scales, including atomic structure, in which negative charge is attracted to positive only up to a point, and positive repels positive only up to a point.

Mass Concentration and Vacuum

Protons are 1,836 times more massive than electrons. As a result, most of the mass of the atom is located in the nucleus. The nuclear radius and atom radius differ by a factor of around 10^5. The electron region is therefore mostly empty.

Probabilistic Nature of Small Particles

As quantum mechanics describes, the less massive that a particle is, the more wavelike it behaves. Therefore, a proton acts more solid than an electron, whose location is more cloud-like and ambiguous.

Noncollapsing Atom

There is a minimum size of electron orbit, preventing electrons from collapsing into the nucleus. It is called the ground level. The wavelike nature of the electron prevents it from being confined to a smaller volume.

Protons Do Collapse

Protons do collapse into each other despite their electrostatic repulsion. A force 100 times stronger than electric charge (at short range) called the "strong force" arises from the quarks inside neutrons and protons.

Chemical Bonds

As electrons build up in shells of orbits, the smaller orbits filling first. The outer shell is the one involved in molecular bonding and chemical reactions. A full outer shell is highly stable so molecular bonds form in ways to fill them.

References

• Arthur Beiser; Concepts of Modern Physics; 1987