Exceptions to trends [ENDORSED]

[alyssawhite1L]

In discussion, I became a bit confused about the exceptions to the trends the relative E.A, I.E, and radii as you move down and across the periodic table. For example, group 15 has a higher ionization level than group 16? Can someone please clarify if this exception applies to all 3 of these trends?

[alyssawhite1L]

It would also be helpful if someone could explain why these exceptions exist for each trend it applies to

[Rachel Formaker 1E]

The ionization energies of the Group 15 elements is higher than that of the Group 16 elements because in Group 15, each p-orbital has one electron, which is relatively stable because it is a half-filled subshell.
Group 16 elements have one set of paired electrons in the p-orbital, and the repulsion between these two electrons in the same orbital raises their energies and makes it easier to remove one of them, causing a lower first ionization energy for the Group 16 elements.

[Chem_Mod]

This is correct. Ionization energy increases to the right of the periodic table and up the periodic table. Remember that ionization energy is the energy it takes to remove an electron. The lower an element is down the periodic table, the larger the energy level. This means those electrons are further away from the nucleus and do not feel the pull from the positive charge of the nucleus. Therefore, they are easier to "pluck off." As you move across the periodic table, the number of protons increases, which provides a stronger attraction for the electrons to be pulled into the nucleus, making them essentially closer. This will make them harder to "pluck off".

Atomic Radii decreases up the periodic table and to the right of the periodic table. This is similar to the reasoning above. The energy level increases down the periodic table, placing electrons further from the nucleus and increasing the effective atomic radius. Across the periodic table to the right, the number of protons increases, increasing attraction, pulling electrons closer, making the radius smaller.

Electron Affinity measures the energy released when adding an electron to an atom. This also relates to ionization energy. It increases to the right of the periodic table and up the periodic table. As you move to the right of the periodic table, the elements really want to gain electrons to achieve the state of their very stable noble gas. They are very close to being fulfilled. Remember that elements want to be in the most stable condition! Therefore, their electron affinity (how much they want electrons) is high. However, at the bottom of the periodic table, these elements are not as attracted to the nucleus since it has a large atomic radius. Therefore, they will not release much energy if an electron is added since it doesn't really want to go there. Its charge will not be as balanced there.

Hope this helps!

[alyssawhite1L]

So to clarify, the group 15/16 exception only applies to the trends of IE, and not EA and Radii? Why is this?

[alyssawhite1L]

Or even better, what are the exceptions for EA and atomic radii?

[Amanda Hagen 1L]

This exception between group 15 and 16 only applies to ionization energy. It does not apply to atomic radius because atomic radius doesn't involve the amount of energy when removing electrons, just the size changes when they are added. It does not apply to electron affinity because electron affinity involves the addition of an electron not the removal.