1. Unit 3 – Lesson 3
Periodic Table

2. Lesson 3 . Periodic Table Trends
There are 109 individual squares, each showing the element name, element symbol, atomic number and atomic mass. Some tables show more information.

3. Atomic Radius
Distance from the center of the nucleus to the outermost orbital
Atoms get larger going down a group because each is one energy level bigger (“n” increases)
Atoms get smaller going across a period because more protons (+) are pulling the electrons towards the nucleus (greater Z efficiency)
Z Efficiency: As you increase the number of protons in the nucleus of the atom, you increase the effective nuclear charge of the atom (Zeff), and the nucleus pulls more strongly on the entire electron cloud. This makes the atomic radius decrease in size.
Distance from center of an atom to the outermost electron
This distance must be estimated since the atom is not solid

4. Atomic Radii Decrease in atomic radius (generally)
Increase in atomic radius (generally)

5. Ionic Radius Size of ions
Atoms that lose electrons, lose their whole outer shell, thus they become smaller.
Atoms that gain electrons become bigger because the extra electrons repel each other and space out more.
Ions are atoms that gain or lose electrons to get a full outer shell

6. Ionic Radii negative ions decrease Positive ions decrease
Increase in ionic radius (generally)
Largest negative ion As3-
Largest positive ion Fr +

7. Ionization Energy
Energy needed to pull off one electron (make an atom an ion) from a gaseous atom.
The higher the ionization energy, the more difficult it is to remove an electron
Atoms with a small atomic radius have a large ionization energy.
Why? – if the radius is small, the nucleus has a larger attractive force on the electron.
Atoms with a large electronegativity have a large ionization energy.
Why? –If the atom wants to gain electrons, it is going to be very difficult to take electrons from it.
Octet Rule – 8 electrons in outer shell. H and He only need 2 electrons.
Metals lose there outer shell to get a full stable ion.
Nonmetals gain electrons to get a full outer shell.

8. First Ionization Energy
Increase in first ionization energy (generally)
Decrease in ionization energy (generally)

9. Electronegativity Ability to attract electrons in a chemical bond
Electronegativity increases from left to right across a period
Why? – Elements on the right side of the periodic table have a larger (+) charge in the nucleus and are closer to attaining 8 valence electrons
Electronegativity decreases as you go down a group
Why? – As you move down the table the valence electrons get further from the (+) nucleus

10. Electronegativity Increase in electronegativity
Noble gases are left out since they are not known to readily form compounds
Electronegativity
Increase in electronegativity
F is the most electronegative
Decrease in electronegativity
Fr is the least electro-negative

11. Summary Francium, Fr Large radius Low ionization energy
Low electronegativity
Fluorine, F
Small radius
High ionization energy
High electronegativity

12. Sample Problem (a) aluminum (b) carbon
Boron, carbon, and aluminum occur near each other in the periodic table. Use the periodic table to identify which of these elements is
(a) the largest atom, and
(b) the atom with the highest ionization energy.
(a) aluminum
(b) carbon

13. Examples Compare the following atoms: F, Br, At Which has the largest:
Electronegativy?
Atomic Radius?
1st Ionization energy?

14. Examples Compare the following atoms: K, Cu, Kr Which has the largest:
Electronegativy?
Atomic Radius?
1st Ionization energy?

15. Trends in Metallic Character
Metals have a higher tendency to lose electrons in order to achieve the stability of a filled octet
Valence electron farther from nucleus = easier to lose electrons
As electronegativity or ionization energy increases, metallic character decreases

16. Trends in Metallic Character
Metals have a higher tendency to lose electrons
Valence electron farther from nucleus = easier to lose electrons