1. Periodic Trends

2. Atomic Radius
The distance from the nucleus out to the valence shell (outermost energy level occupied by electrons)
Measured in
angstroms ( )

3. How Radius Is measured The point at which the valence shell “ends” is
difficult to measure.
Instead, the distance
between the nuclei of 2
bonded atoms is divided
by 2, as nuclei are more
easily detected

4. Atomic Properties affecting radius
Energy Levels:
The more energy levels required to hold an atom’s electrons, the larger the radius will be.
As each energy level gets further and further from the nucleus.

5. Atomic Properties affecting radius
Electron Shielding: Core electrons block (shield) the positive charge of the nucleus that the outer (valence) electrons feel.

6. Atomic Properties affecting radius
Electron Shielding:
The more core electrons present, the more shielding of the nuclear charge.
The more the positive charge is shielded, the larger the radius will be as the attraction force between the electrons and protons will be less.

7. Atomic Properties affecting radius
Nuclear Charge
The overall positive charge emitted
from the nucleus due to the number
of protons present.
The more protons in the nucleus, the greater the charge.
The greater the nuclear charge,
the greater the attractive force
between the nucleus and the
orbiting electrons, the smaller the radius.

8. Nuclear Charge vs. electron shielding
Nuclear charge & electron shielding work against each other, often canceling each other out.
This results in an “effective
nuclear charge”, or the
charge valence electrons
actually feel after the
affects of shielding by core
electrons.
What is the effective charge felt
by sodium’s 1 valence electron?

9. Effective Nuclear Charge

10. Periodic Trend for radius
Increases down a group, decreases across a period.
Why?!

11. Explaining Radius trends
Down a group Reason:

12. Explaining Radius trends
Across a period Reason:

13. Affects of Atomic Radius
Atomic Radius is the determining factor behind the characteristics of Electronegativity and Ionization Energy.
In other words, you can explain why an atom has a certain electronegativity or ionization energy by referencing its radius.

14. Electronegativity
The ability of an atom to attract another atom’s valence electrons towards itself.

15. Electronegativity
Remember that, when atoms bond, they attempt to share or give/receive valence electrons.
Electronegativity is a measure of how well an
atom can steal away
another atom’s valence
electrons.

16. Electronegativity
Radius is the determining factor for electronegativity.
The closer an atom can
get it’s nucleus (positive
attractive force) to the
valence electron it is
trying to steal, the more
it can attract it

17. Electronegativity
When we say the radius is the determining factor for electronegativity, we are also saying that the balance between the nuclear charge, electron shielding, and the number of energy levels determines electronegativity
Because they determine radius!

18. Trends for Electronegativity
Radius and Electronegativity are inversely related (as one increases, the other decreases)

19. Ionization energy
The energy required to remove a valence electron from an atom (how hard it is to remove).

20. Ionization energy
Radius is the determining factor for ionization energy.
The closer an atom’s nucleus
(positive attractive force) is to
it’s own valence electrons
the more it can attract them
and the harder they will be
to remove.

21. Ionization energy
Again, when we say the radius is the determining factor for ionization energy, we are also saying that the balance between the nuclear charge, electron shielding, and the number of energy levels determines ionization energy.
Because they determine radius!

22. Trends for ionization energy
Radius and Ionization Energy are inversely related (as one increases, the other decreases)

23. Ionization Energy and Electronegativity
Both ionization energy and electronegativity describe how an atom handles valence electrons
Whether it is good at taking electrons or good at giving them
Therefore, it should be no surprise that we use this information to determine how they bond and what types of bonds these atoms make!
Bonds