ALL Periodic Table Trends Influenced by three factors: 1. Energy Level Higher energy levels are further away from the nucleus. 2. Charge on nucleus (# protons) More charge pulls electrons in closer. (+ and – attract each other) 3. Shielding effect (blocking effect?) 1

Shielding The electron on the outermost energy level has to look through all the other energy levels to see the nucleus. Second electron has same shielding, if it is in the same period 2

What do they influence? Energy levels and Shielding have an effect on the GROUP Nuclear charge has an effect on a PERIOD

Trends in Ionization Energy Ionization energy is the amount of energy required to completely remove an electron (from a gaseous atom). Removing one electron makes a 1+ ion. X + energy --> X+ + e- The energy required to remove only the first electron is called the first ionization energy. 4

Ionization Energy - Period trends All the atoms in the same period have the same energy level. Same shielding. But, increasing nuclear charge From left to right, the electrons therefore become more tightly held meaning it takes more energy to pry them loose. So IE generally increases from left to right 5

Ionization Energy - Group trends As you go down a group, the IE decreases because... The electron is further away from the attraction of the nucleus, and There is more shielding. 6

He has a greater IE than H. Both elements have the same shielding since electrons are only in the first level But He has a greater nuclear charge H First Ionization energy Atomic number 8

These outweigh the greater nuclear charge First Ionization energy Li has lower IE than H more shielding further away These outweigh the greater nuclear charge H First Ionization energy Li Atomic number 9

greater nuclear charge First Ionization energy He Be has higher IE than Li same shielding greater nuclear charge First Ionization energy H Be Li Atomic number 10

First Ionization energy Atomic number 11

Driving Forces Full Energy Levels require lots of energy to remove their electrons. Noble Gases have full orbitals. Atoms behave in ways to try and achieve a noble gas configuration. 12

Trends in the Periodic Table Electron Affinity The energy that is absorbed or released during the addition of an electron to a neutral atom. X (g) + e- → X- (g) + energy Generally, the energy that results from this process (the electron affinity) is negative or close to zero The electron affinity is a measure of the attraction between the incoming electron and the nucleus - the stronger the attraction, the more energy is released 13

Electron Affinity: Trends Across the row Electron affinities becoming increasingly negative from left to right. Atoms with close to full valence shells will tend to gain electrons. Such atoms (on the right of the periodic table) have very negative electron affinities, meaning they give off a great deal of energy upon gaining an electron and become more stable Down the group Electron affinities change little moving down a group, though they do generally become slightly more positive (less attractive toward electrons).

Trends in the Periodic Table Increasing Atomic Radius Decreasing IE Decreasing Atomic Radius © 1995-2002. Prentice-Hall, Inc. 16