AS chemistry

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Author:
ghoran
ID:
244653
Filename:
AS chemistry
Updated:
2013-11-10 05:02:41
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unit one atomic structure
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revision
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  1. explain the graph 
    • this graph tells us about the number of electrons in each main level or orbit : 2, 8 , 1 
    • the eight electrons are in fact sub-divided into two further groups that correspond to the 2s^2 , 2p^6 electrons in the second main level , but this is not visible on the scale of figure 1 
    • the graph shows a general increase as more energy is needed to remove successive electrons 
    • successive electrons are harder to remove because the nucleus is attracting fewer electrons and therefore the remaining electrons are more strongly attracted 
    • there are significant increases in energy as we move to lower main energy levels , this is because the lower main energy levels are closer to the nucleus and the electrons are more strongly attracted the nucleus the closer they are to the nucleus . This is because the strength of the electrostatic force of attraction between the positive nucleus and negative electrons decreases the further apart they are
  2. explain the graph

    and use the second graph to help explain the decrease in ionisation energy between magnesium and aluminium
    • the ionisation energy generally increases as we go across the period . this is because the nuclear charge is increasing (this is because the number of protons is increasing) and this therefore makes it more difficult to remove an electron . This because the electrons are being removed from the same main energy level so there is increasing attraction between the nucleus and electron to be removed since the number of protons is increasing 
    • between magnesium and aluminium there is a decrease in first ionisation energy . This is because the outer electron in magnesium is removed from the 3s sublevel whereas in aluminium it is removed from the 3p sublevel . The 3p sublevel is further from the nucleus so there's a weaker force of attraction between the positive nucleus and electron to be removed so there's less energy required to remove the electron 
    • between P and S there is also a decrease in first ionisation energy . This is because the outer electron in S is paired in a 3p orbital . the mutual repulsion between the paired electrons makes the outer electron in S easier to remove
  3. explain the graph 
    there is a general decrease in first ionisation energy as we descend the group . this is because as we descend the group , elements have their outer electron in an additional main energy level , this means the electron to be removed is further away from the nucleus so there is a weaker force of attraction between the negative electron to be removed and the positive nucleus so the electron to be removed can be removed more easily
  4. why is the ionisation energy of every element endothermic 
    heat or energy is needed to overcome the attraction between the negative electron and positive nucleus 
  5. explain why the first ionisation energy of neon is higher than that of sodium 
    the outer electron in Ne is in 2p whereas the outer electron in Na is in 3s . 2p is closer to the nucleus and less shielded from the nuclear charge 
  6. the Ne atom and Mg2+ ion have the same number of electrons . give two reasons why the first ionisation energy of neon is lower 
    • neon has fewer protons 
    • Mg2+ is charged and it is harder to remove electrons from a charged species - there's a greater attraction between a 2+ ion and its electrons than between an atom and its electrons 
  7. describe and explain the trend in atomic radius of the elements Na to Cl in period 3
    • decrease 
    • as the number of protons increases , the positive charge of the nucleus increases this means that the electrons are pulled closer to the nucleus , making the atomic radius smaller . the extra electrons that the elements gain across a period are added to the outer energy level so they don't really provide any extra shielding effect 
  8. explain why the third ionisation energy of magnesium is very much larger than the second ionisation energy of magnesium
    the electron to be removed in third ionisation is in a lower energy level which is closer to the nucleus and less shielded by inner electrons this results in a stronger attraction to the nucleus 
  9. state and explain the trend in first ionisation energy of the elements Mg to Ba
    • decreases 
    • outer electrons further from nucleus and more shielded by inner electrons , this results in a weaker attraction to the nucleus

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