Physical chemistry 1
Atomic structure
Fundamental particles
Developing ideas of the atom
• Greek philosophers had a model where matter was made up of a continuous substance making 4
elements – air, earth, fire and water.
• The fact matter was made up of individual atoms wasn’t taken seriously until another 2000
years.
• Alchemists built up a lot of evidence about how substances change and combine – trying to turn
metals into gold.
• 1661 – Robert Boyle proposed that some substances couldn’t be made simpler – chemical
elements.
• 1803 – Henri Becquerel discovered radioactivity, showing particles could come from inside the
atom, so it wasn’t indivisible.
• 1804 – J.J Thompson discovered the electron, the first sub-atomic particle to be discovered. He
showed electrons were negatively charged and were the same for all elements.
• As electrons were negative but atoms were neutral, there had to be a source of positive charge.
• Electrons were much lighter than the atom, so something had to be making up the rest of the
mass.
• J.J Thompson suggested the plum pudding model.
• 1911 – Ernest Rutherford and his team found that most of the mass and all the positive charge
was in a tiny central nucleus.
• It’s been known that atoms are made up of sub-atomic particles for years – the full picture in still
being built up in “atom smashers”. E.g., at CERN.
Sub-atomic particles
• Protons, neutrons and electrons.
• Protons and neutrons form the nucleus and are nucleons.
• Electrons surround the nucleus
Property Proton p Neutron n Electron e
Mass (kg) 1.673x10-27 1.675x10-27 0.9x10-30
-19
Charge (C) +1.602x10 0 -1.602x10-19
• The numbers are very small, so in practise relative masses and charges are used:
Property Proton p Neutron n Electron e
Relative mass 1 0 1/1840
Relative charge +1 0 -1
• In a neutral atom, the number of protons and electrons are equal.
Atomic structure
Fundamental particles
Developing ideas of the atom
• Greek philosophers had a model where matter was made up of a continuous substance making 4
elements – air, earth, fire and water.
• The fact matter was made up of individual atoms wasn’t taken seriously until another 2000
years.
• Alchemists built up a lot of evidence about how substances change and combine – trying to turn
metals into gold.
• 1661 – Robert Boyle proposed that some substances couldn’t be made simpler – chemical
elements.
• 1803 – Henri Becquerel discovered radioactivity, showing particles could come from inside the
atom, so it wasn’t indivisible.
• 1804 – J.J Thompson discovered the electron, the first sub-atomic particle to be discovered. He
showed electrons were negatively charged and were the same for all elements.
• As electrons were negative but atoms were neutral, there had to be a source of positive charge.
• Electrons were much lighter than the atom, so something had to be making up the rest of the
mass.
• J.J Thompson suggested the plum pudding model.
• 1911 – Ernest Rutherford and his team found that most of the mass and all the positive charge
was in a tiny central nucleus.
• It’s been known that atoms are made up of sub-atomic particles for years – the full picture in still
being built up in “atom smashers”. E.g., at CERN.
Sub-atomic particles
• Protons, neutrons and electrons.
• Protons and neutrons form the nucleus and are nucleons.
• Electrons surround the nucleus
Property Proton p Neutron n Electron e
Mass (kg) 1.673x10-27 1.675x10-27 0.9x10-30
-19
Charge (C) +1.602x10 0 -1.602x10-19
• The numbers are very small, so in practise relative masses and charges are used:
Property Proton p Neutron n Electron e
Relative mass 1 0 1/1840
Relative charge +1 0 -1
• In a neutral atom, the number of protons and electrons are equal.
