Chemistry · Class 8–10

Structure of an Atom

Build an atom from the inside out — nucleus, protons, neutrons and electron shells.

syllab.in · free

🧠 Remember it

Structure of an Atom

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."

🌏 In real life

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.

📝 Quick notes

  • 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.

🎯 Test yourself

What is the maximum number of electrons the L shell (n = 2) can hold?

8, using 2n² = 2 × 2² = 8.

Learn it fully — free

See the animated, step-by-step Structure of an Atom lesson on Syllab

syllab.in

Open the full lesson