GCSE Chemistry (AQA)

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Development of the Atomic Model

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Atomic structure and the periodic table A simple model of the atom, symbols, relative atomic mass, electronic charge and isotopes

Development of the Atomic Model

10:14 Development of the Atomic Model
Spec 4.1.1.3
Previous Chromatography Next Development of the Later Atomic Models
  • Ideas about atoms have evolved over time due to new experimental evidence.
  • Atoms are incredibly small and cannot be seen directly; scientists make theories and predictions about their structure.
  • Early atomic models were simple and evolved into the current atomic structure.
  • Initially, atoms were thought to be indivisible spheres, a concept from ancient Greeks.
  • Discovery of the electron led to the plum pudding model, suggesting atoms are positive spheres with embedded negative electrons.
  • The plum pudding model was challenged by the alpha particle scattering experiment led by Ernest Rutherford.
  • Alpha particles, consisting of two protons and two neutrons, were directed at gold foil.
  • The experiment showed some particles passed through, some deflected slightly, and a few deflected significantly.
  • This led to the nuclear model of the atom, with a concentrated positive nucleus and electrons surrounding it.
  • Key differences between the plum pudding and nuclear models:
  • Plum pudding model: no nucleus, solid, evenly distributed positive charge, mass spread throughout, electrons embedded.
  • Nuclear model: small, dense, positively charged nucleus, mostly empty space, concentrated positive charge in nucleus, mass in nucleus, electrons orbiting nucleus.

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