Atom As A System

Atomic structure

At the scale of an atom, almost all the mass is concentrated in a tiny nucleus. Electrons occupy quantum states around it rather than little planetary tracks. The atomic number counts protons and identifies the element.

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→ Atomic structure

The atomic nucleus

The nucleus contains protons and neutrons bound by the strong nuclear interaction. Nuclear size, binding and stability depend on the balance of several physical effects.

Nuclear structure explains isotopes, radioactivity, nuclear energy and much of the origin of the chemical elements.

→ The atomic nucleus

Atomic orbitals

An atomic orbital is a quantum-mechanical description associated with an electron state in an atom, not a tiny classical path.

The familiar s, p, d and f labels organize electronic structure and help make sense of the architecture of the periodic table.

→ Atomic orbitals

Atomic energy levels

Bound electrons in atoms occupy quantized energy states. Transitions between states can involve absorption or emission of photons whose energies match the energy difference.

Discrete atomic spectra are direct experimental evidence that atomic energies are not continuous.

→ Atomic energy levels

Sources

IUPAC Gold Book · NIST · BIPM