1. Electronegativity
mmm…electrons
Fluorine.

2. Electronegativity is the measure of the ability of an atom in a molecule to attract electrons to itself.

3. TREND
increases from left to right across a period and decreases down a group.

5. Why?
Attraction experienced by an electron towards a particular nucleus depends on:
Number of protons in nucleus
Atomic radius
Amount of electron screening
Why increased EN across period?
REASON: Number of protons in the nucleus increases = increased electron attraction towards nucleus
REASON: decreased atomic radius= increased electron attraction towards nucleus
Why decreased EN down a group?
REASON: Atomic radius increases down the group= decreased electron attraction towards nucleus
REASON: Increased electron shielding down the group = decreased electron attraction towards nucleus

6. Exceptions
Gallium and germanium have higher EN than aluminum and silicon
Elements in the 6th period to the 12th period (transition metals) increase EN down the group.

7. Possible explanations
Due to phenomenon called d-block contraction, the addition of full a d-orbital decreases the atomic radius to size close to 3rd period size
Reason why Ga is smaller than Al and thus more EN
Certain transition metals have unusually small atomic radii
because the d-electrons are not as effective in shielding outer electrons from the increasing positive nucleus

8. Usage?
Fake trend. Sorry.

9. Electronegativity is a relative scale used to determine polarity and ionic character of bonds
Not based on a measurable scale
Pauling scale commonly used
F = 4.0
Cs= 0.7
the difference in electronegativities more important than individual values
small difference between electronegativities of elements in a compound = low polarity
Large difference electronegativities = very polar

10. The B—F bond is more polar because > for the B—F than the B—Cl
Example
Ex: What would have a more polar bond:
B—F or B—Cl ?
Solution:
The B—F bond is more polar because > for the B—F than the B—Cl

11. Polarity and Ionic character
As increases, the ionic character of the bond also increases
Small yields a more covalent bond
Larger yields a more ionic bond

12. El Fin.