1. Periodic Trends Two things affecting periodic behavior of atoms
Distance of electrons from nucleus
Attraction between the nucleus and the electrons

2. Trends – Atomic Size Atomic Size is measured by Atomic Radius
Trend – L to R
It decreases left to right because as you move L to R the attraction for the electron increases as a result of the large nucleus thereby making the atom smaller.
Trend – T to B
It increases top to bottom because as you move T to B the number of energy levels increases thus increasing the size of the atom

3. Trends – Ionic Size
Change in size due to the loss or gain of an electron
Cation – loss of electron – smaller than atom
Anion – gain of electron – larger than atom
Trend – L to R
It decreases left to right because as you move L to R the attraction for the electron increases as a result of the large nucleus thereby making the atom smaller.
Trend – T to B
It increases top to bottom because as you move T to B the number of energy levels increases thus increasing the size of the atom

4. Trends – Electronegativity
Tendency of an element to attract electron when combined with another element
Trend – L to R
It increases left to right because as you move L to R the attraction for the electron increases as a result of the large nucleus so the nucleus will be more likely to attract additional electrons.
Trend – T to B
It decreases top to bottom because as you move T to B the addition of energy levels “blocks” the attraction of the nucleus for electrons (shielding) which decreases the likelihood of the element to attract electrons.

5. Trends – Ionization Energy
Energy required to remove an electron from an atom
Trend – L to R
It increases left to right because as you move L to R the attraction for the electron increases , so more energy is required to remove an electron from an atom
Trend – T to B
It decreases top to bottom because the addition of energy levels decreases the “pull” of the nucleus on the outer electrons making it easier for them to be removed.

6. chalcogens halogens electronegativity (across a row) f block actinoids
group 14
electronegativity
(across a row)
oxygen group
chalcogens
actinoids
same column
f block
Principle Quantum #
radii across a row
increases
s2p5
transition metals
(down a column)
ionization energy
row 6
decreases