The document discusses periodic trends and how atomic radius is related to atomic number. It states that atomic radius decreases from left to right across a period as atomic number increases due to greater nuclear charge. Atomic radius increases down a group as additional principal energy levels are added and electrons are farther from the nucleus.

1. Periodic Trends
( Relationship between Atomic number
and Atomic Radius)
Presented by:
Marian Desiree G. Suba
BSED 3-A

2. Definition of Terms
• Atomic number – is the number of
protons in the nucleus of an atom of the
element.
• Atomic radius – isthe distance from the
center of the nucleus to the outer edge of
the electron cloud.

3. Atomic Number Trend
• From left to right, the atomic
number increases.
• From top to bottom, the atomic
number increases.

4. atomic number increases
atomic
number
increases

5. Atomic Radius Trend
• From left to right, the atomic radius
decreases.
• From top to bottom, the atomic
radius increases.

7. Take a look at the table for the elements in
Period 3 of the Periodic table:

8. Examine the graph. Compare this with the
previous table.

9. Explanation of the trend
Going across Period 3:
• the number of protons in the nucleus increases so ...
• the nuclear charge increases ...
• there are more electrons, but the increase in shielding is
negligible because each extra electron enters the same
principal energy level ...
• therefore the force of attraction between the nucleus and the
electrons increases ...
• so the atomic radius decreases.

10. Summary
• Atomic radius decreases as you go left to right because
of the greater amount of protons. The higher the atomic
number, the greater number of protons. The protons will
pull the electrons closer to its nucleus thus resulting in a
smaller atomic radius.
• Atomic radius increases as you go down the group
because as you go down the group, you add another
principal energy level. The more energy levels, the further
the electrons will be from the nucleus resulting in a a
smaller atomic radius.

11. Evaluation
A. Arrange the following elements according to decreasing
atomic radius.
1. Ca, Ge, Rb
Answer: ________________
2. I, Ba, Sr
Answer: ________________
3. Cs, Pb, Ne
Answer: ________________
4. Bi, Sb, As
Answer: ________________
5. Ga, Na, Mg
Answer: ________________

12. Evaluation
B. Arrange the following elements according to increasing
atomic radius.
1. Kr, Ca, Sr
Answer: ________________
2. As, Sb, Po
Answer: ________________
3. Si, N, O
Answer: ________________
4. Ba, Cl, K
Answer: ________________
5. Na, Mg, Ga
Answer: ________________

13. Assignment
• Read more about Periodic Trends.
• Answer the following:
1. Define ionization energy.
2. What is the trend for ionization energy?
3. Define electron affinity.
4. What is the trend for electron affinity?