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Chemistry · Ch 2 — Structure of Atom

Atomic Models

2.2

Atomic Models

Before turning to how these particles are arranged inside the atom, it is worth collecting in one place what the discharge-tube and oil-drop experiments established about each of them — their charges, masses and symbols. Table 2.1 summarises the three fundamental particles.

Table 2.1Properties of Fundamental Particles
NameSymbolAbsolute charge/CRelative chargeMass/kgMass/uApprox. mass/u
Electrone−1.602176×10−19-1.602176 \times 10^{-19}−1-19.109382×10−319.109382 \times 10^{-31}0.000540
Protonp+1.602176×10−19+1.602176 \times 10^{-19}+1+11.6726216×10−271.6726216 \times 10^{-27}1.007271

The experiments that revealed electrons, protons and neutrons demolished Dalton's picture of the indivisible atom. Once scientists knew that atoms contain both positive and negative charges, different atomic models were needed to explain, among other things:

  • the stability of the atom — opposite charges attract, so what prevents the electron from crashing into the nucleus?
  • the comparative behaviour of elements — how do physical and chemical properties arise from internal structure?
  • the formation of molecules — how and why do atoms combine?
  • the origin and nature of electromagnetic radiation absorbed or emitted by atoms. …
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