Structure of an Atom — Interactive Diagram
Build an atom from the inside out — nucleus, protons, neutrons and electron shells.
TL;DR: Build an atom from the inside out — nucleus, protons, neutrons and electron shells.
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Structure of an Atom: Build an atom from the inside out — nucleus, protons, neutrons and electron shells.
Why it matters: Protons, neutrons, electrons and shells explain the whole periodic table, ions and bonding — the foundation of all chemistry.
Structure of an Atom — Step by Step
- At the centre is the NUCLEUS — packed with positively charged PROTONS and neutral NEUTRONS. It holds almost all the atom’s mass.
- ELECTRONS (negatively charged) move around the nucleus in fixed energy SHELLS — like planets around the Sun.
- Example — a CARBON atom: 6 protons, 6 neutrons in the nucleus and 6 electrons (2 in the inner shell, 4 in the outer). That outer count decides how it bonds.
Quick Notes — the Exam Crux
- An atom = a nucleus (protons + neutrons) surrounded by electrons in shells.
- Proton: +1 charge, mass ≈ 1u. Neutron: 0 charge, mass ≈ 1u. Electron: −1 charge, negligible mass.
- Atomic number (Z) = number of protons = number of electrons in a neutral atom.
- Mass number (A) = protons + neutrons.
- Maximum electrons in a shell = 2n² (K=2, L=8, M=18, N=32).
- Valence (outermost-shell) electrons decide chemical behaviour and bonding.
- Isotopes = same number of protons but different neutrons (e.g. C-12 and C-14).
Remember It (Memory Trick)
Positive protons and neutral neutrons sit in the tiny nucleus; negative electrons orbit in shells. Shell capacity = 2n² (K=2, L=8, M=18). "Protons Push in the centre, Electrons Everywhere else."
Real-Life Example
A hydrogen balloon rises while a helium balloon floats gently at a birthday — the two behave differently because their atoms differ by just one proton. Atomic structure decides an element's entire personality.
Test Yourself
What is the maximum number of electrons the L shell (n = 2) can hold?
8, using 2n² = 2 × 2² = 8.
How do you calculate the number of neutrons in an atom?
Neutrons = mass number (A) − atomic number (Z).
What are isotopes?
Atoms of the same element with the same number of protons but different numbers of neutrons.
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