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I was just wondering if anyone could help me by telling me the trends and why that trend exists in the periodic table for the following:

  1. Atomic Size
  2. Ionization Energy
  3. Metallic Character
  4. Positive ion size
  5. Negative ion size
  6. Electronegativity

My Progress (if my reasoning is wrong for any of these please correct me):

1) Atomic Size - I memorized from my class lecture that the greatest atomic size is towards the bottom-left of the periodic table. I think the reason for this is because as you go down the groups (IA,IIA etc.) you add more electrons. Adding more electrons means the atom will logically grow bigger. I am not sure why the answer is not bottom-right, though.

2) Ionization Energy- This is the energy required to remove an electron from an atom. If there are more electrons then the electron will be further from the nucleus and by Coulomb's law, since the distance increases, the force attraction that keeps the electron in the nucleus's orbit is weak. Thus, the ionization energy is the highest toward the top-left.

3) I have no clue what to think for metallic character.

4) Positive ion size I know the answer is that it increases towards the bottom left, but I don't know why.

5) Negative ion size I know the answer is that it increases towards the bottom left, but I don't know why.

6) Electronegativity I am pretty sure is highest at F which is 4.0 and is lowest towards the bottom left. So the trend increases towards the top-right.

Thank you to anyone who helps clarify this to me!

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1 Answer 1

  1. You are correct on atomic size being due to number of electrons and their shells and the reason why atomic size decreases from left to right is due to the number of the protons being greater on the right than on the left of the periodic table with same number of shells due to shell theory. (Reference).
  2. The concept you are forgetting is Valence Electrons. Atoms are stabilized most often when there outer most shell is filled with 8 valence electrons (except for hydrogen and helium with 0 or 2). The elements on the left side of the periodic table lose electrons easily since they have a very large atomic radius allowing for lower ionization energy. on the right side of the periodic table(nitrogen, oxygen , and halogens) have a smaller atomic radius creating a stronger pull making it harder to lose an electron thus they will steal an electron to become stable.
  3. The best way to summarize this is to quote Chemistry.about.com

    "There are trends in metallic character as you move across and down the periodic table. Metallic character decreases as you move across a period in the periodic table from left to right. This occurs as atoms more readily accept electrons to fill a valence shell than lose them to remove the unfilled shell. Metallic character increases as you move down an element group in the periodic table. This is because electrons become easier to lose as the atomic radius increases, where there is less attraction between the nucleus and the valence electrons because of the increased distance between them."
    (Reference)

  4. Positive ion size decreases due to the lack of electrons which allows for the protons to pull stronger on fewer electrons.
  5. The inverse applies for negative ion size. Due to the fact that there are more electrons, the size will increase since they will occupy more space.
  6. Electronegativity is the pull a elements has on electrons. This determines how it bonds with other elements i.e.(whether it shares or looses electrons). If a element has over a 1.7 Electronegativity difference then these the element with the smaller electronegativity will give away several electrons 1-4. Elements on the left side of the periodic table have the smallest Electronegativity due to their atomic size and inability to gain enough electrons to be stable ions. Elements from left to right in a period show increasing elctronegativity, and electrons form up to down in a group will have a lower electronegativity. Also fluorine has a 3.98 elctronegativity. (Reference).

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Thank you this is perfect! –  Tim Xu Dec 28 '12 at 23:35
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