5.1
nuclear model of the atom
early atomic models
early models suggested atoms were solid spheres or a positive mass with embedded electrons. these models could not explain experimental observations.
alpha particle scattering experiment
rutherford directed alpha particles at thin gold foil and observed how they were scattered.
- most alpha particles passed straight through
- some were deflected by small angles
- a very small number were deflected backwards
conclusions
- the atom is mostly empty space
- positive charge and most mass are concentrated in a small nucleus
- the nucleus is much smaller than the atom
- electrons orbit the nucleus
structure of the atom
- nucleus contains protons and neutrons
- electrons orbit the nucleus at relatively large distances
relative charge and mass
- proton: charge +1, relative mass 1
- neutron: charge 0, relative mass 1
- electron: charge −1, relative mass 1/1836
size of nucleus and atom
the nucleus has a radius of about 10⁻¹⁵ m, while the atom has a radius of about 10⁻¹⁰ m.
this shows that the nucleus is extremely small compared to the size of the atom.