Periodic Trends( Relationship between Atomic number and Atomic Radius)

Presented by:

Marian Desiree G. SubaBSED 3-A

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.

Atomic Number Trend

• From left to right, the atomic number increases.

• From top to bottom, the atomic number increases.

atomic number increases

atomic number

increases

Atomic Radius Trend

• From left to right, the atomic radius decreases.

• From top to bottom, the atomic radius increases.

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

Examine the graph. Compare this with the previous table.

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.

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.

EvaluationA. 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: ________________

EvaluationB. 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: ________________

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?