atomic structure

• Definition of relative atomic mass


  The average mass of all the isotopes of an atom compared to 1/12 the mass of one atom of carbon-12.
• State and explain the general trend of the first ionisation energies of the period 3 elements Na-Ar.


  As the proton number of elements increases, first ionisation energy increases because the number of protons increases so attraction between the nucleus and outermost electrons increases and shielding stays the same
• Explain why the first ionisation energy of sulphur is lower than it would be predicted from the general trend .


  S has 3p4 whilst P has 3p3 so the electron experiences electron pair repulsion.
• Explain why chromium does not fit the trend for electron configuration


  It only has one electron in its 4s orbital before filling 3d
• Explain why copper does not for the trend for electronic configuration.


  It only has one electron in its 4s orbital before filling 3d 1s² ... 3p⁶ 4s¹ 3d¹⁰
• what are isotopes?


  atoms with the same number of protons, but different numbers of neutrons.
• define the mass number


  (represented as A) the total number of protons and neutrons in the atom
• why do isotopes have the same chemical properties?


  they have the same electronic structure
• why may isotopes have varying physical properties?


  they have different masses
• what are the relative masses of the sub-atomic particles?


  protons: 1

  neutrons: 1

  electrons: 1/1840