1. Periodic Trends

2. Atomic Radius
Atomic Radius is defined as half the distance between the center of 2 atoms of the same element just touching each other.
The radius decreases going across a period and increases going down a group.

4. Why Atomic Radius Trends
Why are atoms Larger Going down a group?
Atoms get larger because the higher the energy level, the more orbitals it has, and the further away from the nucleus those orbitals are. Also, more electrons are interfering with the attraction that the nucleus has on the highest energy electrons (shielding)
Why do atoms get smaller going from left to right across the table?
Atoms get smaller because there is an increase in the effective nuclear charge (more protons attracting more electrons) so the highest energy level gets pulled in closer to the nucleus

5. Ionization Energy
Ionization energy is the energy required to completely remove an electron from a gaseous atom or an ion.
Ionization energy increases going across a period and decreases going down a group.

6. Electronegativity
Electronegativity is a measure of attraction of an atom for the electrons in a chemical bond.
Electronegativity increases going across a period and decreases going down a group.

7. Size Matters for Periodic Trends
Ionization Energy and Electronegativity have the same periodic trend.
In smaller atoms, valence electrons are closer to the nucleus so experience stronger attraction to the nucleus. Therefore they are harder to pull away from an atom
In large atoms, valence electrons are further away from the nucleus so experience less attraction to the nucleus, therefore valence electrons are easier to remove

8. Trends Summarized