1. Periodic Trends
Section 6.3

2. Four Periodic Trends Atomic Radius Ionic Radius Ionization Energy
Electronegativity

3. Trends in Atomic Size
The size of an atom is expressed as atomic radius.
Atomic Radius is ½ the distance between the nuclei of two atoms of the same element when the atoms are joined.
Distance is measured in picometers.
There are 1 trillion pm in 1 meter.

4. Trends in Atomic Radius
Atomic Size increases from top to bottom within a group.
This is due to shielding effect. The inner electrons shield the outer electrons from the nucleus. So, the nucleus has less pull. Therefore, the atom gets bigger down a group.

5. Trends in Atomic Radius
Atomic size usually decreases across a period from left to right.
This is due to the nuclear charge (which is positive) pulling on the electrons (which are negative.)
The nuclear charge increases causing it to have more pull. It pulls the energy levels in making the atom smaller.

6. Trends in Ionic Radius
An Ion is an atom or a group of atoms with a charge.
Positive ions form when electrons are lost. (cations)
Negative ions form when electrons are gained. (anions)
Cations are always smaller than the atoms from which they form.
Anions are always larger than the atoms form which they form.
Sodium Ion
Chlorine Ion

7. Trends in Ionic Radius
In general, ionic radius increases down a group due to the electron shielding.

8. Trends in Ionic Radius
Ionic radius decreases across a period for the cations, and decreases across a period for the anions due to nuclear charge.

9. Trends in Ionization Energy
The energy required to remove an electron from an atom is called ionization energy.
First Ionization energies are the energies required to remove the first electron.
Second Ionization energy is the energy required to remove the second electron, and so on…

10. Trends in Ionization Energy
Atomic Number
Symbol
Name
1st
2nd
3rd
4th 1 H
Hydrogen
1312 2 He
Helium
2372
5250 3 Li
Lithium
520
7298
11815 4 Be
Beryllium
899
1757
14848
21006 5 B
Boron
800
2427
3659
25025
Lithium only has 1 electron to lose in order to bond. Notice that between 1st and 2nd ionization energies that the number goes up. Because once lithium has lost it’s one electron it becomes stable. Elements like being stable. So, the ionization energy increases.

11. Trends in Ionization Energy
First Ionization energies tend to decrease from top to bottom within a group due to electron shielding.

12. Trends in Ionization Energy
First Ionization energies tend to increase from left to right across a period due to increased nuclear charge.

13. Trends in Electronegativity
Is the ability of an atom of an element to attract electrons when the atom is in a compound.
Notice that noble gases have no values. This is due to the fact that most do not form compounds.
Electronegativity Values Li
1.0 Be
1.5 B
2.0 C
2.5 N
3.0 O
3.5 F
4.0 Na
0.9 Mg
1.2 Al Si
1.8 P
2.1 S Cl K
0.8 Ca Ga
1.6 Ge As Se
2.4 Br
2.8 Rb Sr In
1.7 Sn Sb
1.9 Te I

14. Trends in Electronegativity
In general, electronegativity values decrease from top to bottom within a group due to the shielding effect. The inner electrons shield the nucleus from being able to attract electrons.

15. Trends in Electronegativity
In general, electronegativity values tend to increase from left to right across a period due to an increase in nuclear charge.

16. Summary of Trends

17. Acknowledgements