I.e and electroneg

1. 1
Mr. Shields Regents Chemistry U08 L05

2. Ionization energy
2
Ionization Energy (IE) –
The amount of energy needed to remove an electron
from an atom or ion. Every electron in any atom or ion
has a specific ionization energy.
First Ionization Energy –
The amount of energy needed to remove the 1st electron
from the outermost shell of a neutral (uncharged) atom.

3. 3
Rb + energy  Rb+
+ 1e-
Ionization energies are measured in KJ/mole
1 2 3

4. Ionization Energy 4Some atoms have 2 or more electrons in the valence
Shell. For example, for example alkaline earth elements
such as Mg or Sr
Removing the 1st
electron (first ionization energy) will
always take less energy than the energy necessary to
Remove the 2nd
electron (second ionization energy).
This trend continues. The energy necessary to remove a
3rd
electron is greater than the energy necessary to
Remove the 2nd
and so on

5. Ionization Energy Trends 5The energy necessary to remove a valence electron
Varies from atom to atom in predictable ways:
) Ionization energy increases as each successive
electron is removed
) Ionization energy DECREASES going DOWN a GROUP
) Ionization energy INCREASES as you go ACROSS a
PERIOD
) The noble gases have the highest Ionization energies
) The alkali metals have the lowest Ionization energies

6. 6

7. Ionization Energy - Groups 7So… Why do ionization energies display these
trends in groups and periods? Let’s see …
Ionization energies decrease going down a Group:
Moving down a group the principle energy level increases
- distance of electron from the positive
nucleus increases and there are more electrons
providing inner shell shielding of the nucleus
Therefore the valence electrons are less strongly held
Na 2-8-1 (IE = 496 KJ/Mol) Rb 2-8-18-8-1 (IE = 403 KJ/mol)

8. Ionization Energy - Periods
8Ionization energies across a Period increase:
As we move across a period the principle energy level
of the valence electron doesn’t change
- However Nuclear charge increases across the
period while the distance of the valence electron
from nucleus remains the same
- Therefore valence electrons feel the inc. nuclear
charge more strongly and it takes more energy
to remove them from the atom
+37 n=5 +47 n=5
Rb 2-8-18-8-1 (IE=403 KJ/mol) Ag 2-8-18-18-1 (IE=731KJ/mol)

9. Ionization Energy – Noble Gases
9Noble Gases:
The valence shell octet found in the NOBLE GASES
is a particularly stable electron configuration.
Any change from this config will take unusually
high energy since the net result is “destabilizing”
But the trend of decreasing ionization going down
a group is also true even for the Noble Gases
Ne: 2-8 IE: 2081 KJ/mol
Kr: 2-8-18-8 1351
Rn: 2-8-18-32-18-8 1037

10. 10
Ionization Energy trends

11. 11
2nd
or 3rd
IONIZATION ENERGY:
Once an e-
is removed the positive nuclear charge
per electron is now stronger. So the I.E. to remove
the next electron increases
Secondly, enough electrons are lost to achieve an
octet, removal the next electron would destroy the
very stable octet and the I.E. necessary to remove
the next electron jumps significantly
1st
IE(KJ/Mol) 2nd
IE 3rd
IE
Na: 2-8-1 496 4,560
Mg: 2-8-2 736 1,450 7,730

12. Electronegativity
12When we discussed Intermolecular forces we needed
To be able to specify whether a molecule was polar or
Non-polar.
We had a set of guide lines we used to help determine
Non-polarity. What are they?
So… What is the definition of a polar and a
non-polar molecule?
Electronegativity is a property of an element that
Will help us quantify how polar a molecule is.

13. 13
ELECTRONEGATIVITY:
- A measure of how strongly an element
pulls electrons towards it in a chemical bond
Electronegativity (unlike I.E.) has no units:
EN has an arbitrary scale that ranges from 0 – 4.0
Fluorine’s EN is the highest (4.0)
Francium’s EN is the lowest (about 0.7)
FCs F Fvs
Low EN Hi EN Same or Simialar EN
(polar) (non-polar)
δ+ δ-

14. Electronegativity 14
ALL ELEMENTS have IE values even if they have negative
Oxidation Numbers (gain electrons).
The same is true for electronegativity.
- elements that tend to lose electrons (metals) still
have an electronegativity value (though smaller
than the non-metals)
IE(KJ/mol) Electronegativity
Fr 393 (lowest) 0.7 (lowest)
F 1681 (very hi) 4.0 (highest)

15. Electronegativity 15
Since all Elements have electronegativity values we can
Use these values to:
1) Help determine what molecules are polar
2) What molecules are more polar than others
For example: Consider these two molecules
H-Cl and H-I … both are polar molecules.
Now, which one is MORE polar?
(Hint you’ll need to use EN values)
We’ll talk more about this in the next unit!

16. Electronegativity Trends 16
When considering Electronegativity, the trends are
Very similar to those observed for Ionization Energy
hold true for Electronegativity
- Electronegativity decreases down a Group
- Electronegativity increases across Periods

17. 17
Electronegativity Trends
increasing
decreasing
Noble Gases
Have Zero EN