Mass, Charge & Subatomic Particles (CIE A Level Chemistry)

• The mass of an atom is concentrated in the nucleus, because the nucleus contains the heaviest subatomic particles (the neutrons and protons)
  • The mass of the electron is negligible

• The nucleus is also positively charged due to the protons
• Electrons orbit the nucleus of the atom, contributing very little to its overall mass, but creating a ‘cloud’ of negative charge
• The electrostatic attraction between the positive nucleus and negatively charged electrons orbiting around it is what holds an atom together

The mass of the atom is concentrated in the positively charged nucleus which is attracted to the negatively charged electrons orbiting around it

• Protons, neutrons and electrons behave differently when they move at the same velocity in an electric field
• When a beam of electrons is fired past the electrically charged plates, the electrons are deflected very easily away from the negative plate towards the positive plate
  • This proves that the electrons are negatively charged; like charges repel each other
  • It also shows that electrons have a very small mass, as they are easily deflected

• A beam of protons is deflected away from the positive plate and towards the negative plate
  • This proves that the proton is positively charged
  • As protons are deflected less than electrons, this also shows that protons are heavier than electrons

• A beam of neutrons is not deflected at all
  • Which proves that the particle is neutral in character; it is not attracted to, or repelled by, the negative or positive plate

The lighter electrons undergo much more deflection than the protons