1. Periodic Trends

2. Periodic Table 1896: Dmitry Mendeleyev Periodic Law:
The properties of elements vary in a periodic manner by atomic number

3. Atomic Radius
Calculated using the distance between the two nuclei of atoms when they are involved in a chemical bond.
Atomic radii decrease (↓) moving across a period from left to right.
Stronger attractive forces in atoms between the opposite charges in the nucleus and electron cloud cause the atom to be 'sucked' together a little tighter.

4. Ionization Energy (IE)
The energy necessary to remove an electron from the neutral atom.
It generally increases across a row on the periodic maximum for the noble gases which have closed shells.

5. Electron Affinity
The amount of energy released when an electron is added to the atom in its gaseous state—when an electron is added to an atom, the atom forms a negative ion.
Small numbers indicate that a less stable negative ion is formed.

6. Electronegativity
Electronegativity increases from left to right as we move across a period and decreases as we move down any group or family.
A measure of the attraction an atom has for electrons when it is involved in a chemical bond.
Elements that have high ionization energy and high electron affinity will also have high electronegativity since their nuclei strongly attract electrons.