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Atomic models, particles and isotopes

Atomic structure and the periodic table • Atomic models and isotopes

Key concepts

What you'll likely be quizzed about

  • In the scattering experiment, a beam of alpha particles directed at a thin metal foil yields three primary outcomes: most alpha particles pass through unharmed, some deflect at small angles, and a very small fraction scatter at large angles.
  • Most of the atom is empty space, which allows alpha particles to travel through without interaction.
  • The concentrated positive charge within the atom results in strong electric fields that cause a small number of alpha particles to deflect significantly.
  • These observations discredit models asserting a uniform distribution of positive charge and validate a model featuring a compact, dense, positively charged nucleus.

Flashcards

Test your knowledge with interactive flashcards

Calculate protons, neutrons, and electrons for Mg2+ (Z = 12, A = 24).

Click to reveal answer

For Mg2+, there are 12 protons, 12 neutrons (24 − 12), and 10 electrons because of the loss of two electrons.

Key notes

Important points to keep in mind

Atomic number (Z) equals number of protons and identifies the element.

Mass number (A) equals protons + neutrons; neutrons = A − Z.

Neutral atom: electrons = protons; ion: adjust electrons by the charge.

Most of an atom's volume is empty space; most mass concentrates in a tiny nucleus.

Relative atomic mass is a weighted average using fractional abundances (percent/100).

Typical atom radius ~1 × 10^-10 m; typical nucleus radius ~1 × 10^-15 m.

Plum pudding model fails because it cannot explain large-angle scattering.

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