Atomic structure

• Relative mass of neutron

  1
• Relative mass of proton

  1
• Relative mass of electron

  ~1/2000
• Relative charge of proton

  +1
• Relative charge of neutron

  0
• Relative charge of electron

  -1
• Isotopes of an element have the same number of protons
• Isotopes of an element have different number of neutrons
• Isotopes of an element have the same atomic number but different mass numbers
• Atoms are neutral because they contain equal amounts of positive and negative charges.
• What are scientific models developed based on?

  Experimental evidence
• What should be done if evidence does not fit the scientific model?

  You must change or replace the model
• When was the alpha scattering experiment carried out?


  1911
• aloha scattering experiment


  Fired alpha particles at gold foil if the plum pudding model is true the particles would pass straight through
• Why was the plum pudding model developed?

  To explain that atoms are neutral with negatively charged electrons
• What are the key features of the plum pudding model of the atom?

  • Atoms are neutral overall
  • Contains negatively charged electrons
  • Positively charged "pudding" to balance the charge
• What charge do electrons have in the plum pudding model?

  Negative charge
• What does the term "neutral overall" refer to in the context of the atom?

  It means that the total charge of the atom is zero
• What is the mass of the electrons in the plum pudding model?

  Very small mass
• What is the significance of the "solid sphere" in the solid sphere model of the atom?

  It represents the positively charged part of the atom
• How does the plum pudding model explain the neutrality of atoms?

  By having negatively charged electrons balanced by a positively charged mass
• What are the main components of the plum pudding model?

  • Negatively charged electrons
  • Positively charged "pudding"
  • Overall neutral charge
• Results of alpha scattering experiment

  • Most alpha particles pass through gold foil
  • Some alpha particles deflected at small angles
  • small number of alpha particles deflected straight back
• Properties of nuclear model of atom

  • Atoms are mostly empty space
  • Nucleus is very small compared to atom
  • Nucleus is very dense
  • Nucleus is positively charged
• Activity definition

  Units


  Rate of decay

  Becquerels
• What are protons?

  Protons are positively charged subatomic particles found in the nucleus of an atom.
• How do you calculate the number of neutrons in an atom?

  Number of neutrons = Atomic mass - Number of protons
• What is the total charge of an ion?

  An ion has a charge that is not neutral.
• What distinguishes ions from neutral atoms?

  Ions have a different number of electrons compared to protons.
• Atoms are ionised by removing electrons or adding electrons