Periodic Trends!

There are 3 very important trends on the periodic table, that help in understanding why certain elements do the things they do.

The first of these trends is the atomic radius trend.

• To find the atomic radius, you take one half the distance between the nuclei of of two atoms of the same element when they are joined together.
• As the atomic number increases within a group, the charge on the nucleus and the number of energy levels occupied increases. 
• The increase in positive charge draws electrons closer to the nucleus. The increase in the number of occupied orbitals shields electrons in the highest occupied energy level from attraction of protons in the nucleus. The shielding effect is greater than the effect of the increase in nuclear charge, so the atomic size increases.

Next is the ionization energy trend.

• Ionization energy: the energy needed to remove an electron from an atom
• moving electrons from elements on the left side of the periodic table is easy because they only have 1 or 2 electrons in their outer shell
• moving electrons from elements on the right side of the periodic table is harder because they almost have a full shell.

Lastly is the electronegativity trend. It follows the same sequence as the ionization trend.

• Electronegativity: the ability of an atom to attract electrons when the atom is in a compound
• it is low on the left side because they only have 1-2 electrons in the outer shell
• it is high on the right side because they have nearly a full shell. The are more electronegative because they have a stronger pull to fill that last shell.