1. Periodic Trends Objectives: 1. Define the term periodic trend.
2. Identify four important periodic trends and explain how each reflects the electron configurations of the elements.
Key Terms:
periodic trend, atomic radius, ionization energy, electron affinity, electronegativity

2. Atomic Radius
Atomic Radius is the distance from the center of the atom to its outermost electron.
Atoms get larger as they go down a group (column)
They get larger because the principle energy level increases (1s, 2s, 3s, 4s, ...)
Atoms get smaller as you go left across a period (row) left to right
Since the elements are in the same principle energy level as you go across the period, the size of the element decreases due to the increasing number of protons within the nucleus (think stronger magnet)

3. Ion Radius
The ionic size of an element is different that the neutral size of the element due to the loss or gain in electrons. Here is the general rule:
As atoms lose electrons (1A-4A), the cation size becomes smaller
As atoms gain electrons (5A-7A) the anion size becomes larger

4. Ionization Energy
Ionization energy refers to the energy required to remove an electron from an atom. It is the measure of how strongly an atom holds on to its outer (valence) electrons. Here are some general rules:
The higher the ionization energy, the less likely the atom is to loose an electron (and vice-a-versa)
Ionization energies decrease as you move down a group (column)
Ionization energies increase as you across a period (row) from left to right

5. Second Ionization Energy
Removing each successive electron requires an increased amount of ionization energy. This increase is not linear due in part to the decrease in electron-electron repulsion and increased attraction to its positive core.
Once it reaches its noble core, the energy to remove the next electron greatly increases.

6. Electronegativity
Electronegativity refers to an atoms ability to attract electrons in a chemical bond. There are no units involved nor is it a property but is a relative scale from 1-4.
The trend closely resembles ionization energy
Increases as you move left to right across a period
decreases as you move down a group
Exception: Noble gases have a lower electro negativity that the halogens as they do not participate in bonding.
difference in electronegativity values are used to predict type of bonding