atom and history of atom

• Mass number

  tells us the number of protons and neutrons in the nucleus of an atom
• Atomic number

  Tells us the number of protons in the nucleus
• Ions

  Charged particle that has a different number of electrons compared to protons because it has gained or lost electrons
• Negative ion

  Has gained electrons to gain a full shell of electrons and enables it to form a more stable ionic compound
• Positive ion

  Has lost electrons to gain a full shell of electrons and enable it to form a more stable ionic compound
• Isotope

  elements with the same number of protons but a different number of neutrons
• What year was John daltons discovery?

  1803
• John dalton

  Atoms are solid spheres and each element is made from different spheres
• What year was JJ Thomson's discovery

  1897
• JJ Thomson

  -atoms must contain smaller negatively charged particles known as electrons

  -atom wasn't solid and was made up of other particles

  -developed the plum pudding model
• What year was Ernest Rutherford's discovery

  1909
• Ernest Rutherford

  -Gold foil experiment

  -discovered the nucleus (which was very small and positively charged)

  -atom was mainly empty space

  -a tiny positive sphere in the centre of a cloud of darkness

  -discovered the nuclear model
• Gold Foil Experiment

  Positive alpha particles were fired at a thin gold foil
• Gold Foil Experiment observations

  1)most alpha particles passed straight through the gold foil

  2)some alpha particles were deflected at angles

  3)very few alpha particles bounced straight back from the gold foil
• Gold Foil Experiment Conclusions

  1. Most of the atom is made up of empty space

  2. An atom has a tiny, central nucleus which is positively charged

  3. The centre of the atom (nucleus) contains mass
• What year was Niels Bohr's discovery

  1913
• Niels Bohr

  -if left in a cloud, electrons would collapse on the nucleus

  -electrons must be in shells with fixed energy levels
• Niels Bohr Experimental Proof on Shells

  -when electromagnetic radiation is absorbed, electrons can move from a lower energy level to a higher energy level (excitation)

  -when electromagnetic radiation is emitted, electrons move from a higher energy level to a lower energy level (de-excitation)
• Subatomic particles

  protons, neutrons, electrons
• Relative mass of a proton

  1
• Relative mass of a neutron

  1
• Relative mass of an electron

  1/1836
• Relative charge of a proton

  +1
• Relative charge of a neutron

  0
• Relative charge of an electron

  -1
• Relative atomic mass

  The average mass of an atom of an element compared to 1/12 the mass of a carbon-12 atom
• Mass number is always

  An integer (whole number)
• Relative isotopic mass

  The mass of an atom of an isotope of an element compared to 1/12 the mass of carbon-12 atom
• Relative isotopic mass is always

  A whole number
• Ar equation

  Ar=€(Isotope Mass X abundance)/total abundance

  €= sum of
• Which energy level is the lowest energy

  1st energy level
• Lower energy means

  Closer to the nucleus