1. 7.12 – NOTES Bond and Molecular Polarity Using Models

2. V. Electronegativity and Polarity
A. Electronegativity difference and bond character
Electronegativity difference can determine the type of bond formed:
attraction for bonded e-; F, O, N, Cl (4.0, 3.5, 3.0, 3.0);
metals – low EN; F – O = 0.5
*note that He, Ne and Ar have never made a bond. In the 1960’s Neil Bartlett made first compound with Xe and F; Kr and Rn have also been made into compounds with F

3. Percentage ionic character:
how much of the time is this compound ionic?
How much of the time is the e- transferred, even the most ionic bonds have some covalent tendencies;
1.7 and up is usually ionic;

5. Case #1 Electrons equally shared – Nonpolar covalent bond (npc)
Equal sharing of electrons, no poles; Atom A and B share electrons equally, 50-50;
EN difference near 0; (0 to .4)

7. Case #2 Electrons shared, but not equally – Polar covalent bond
Atom A and B share, but one is more “greedy” than the other b/c has higher EN;
δ is symbol used to show partial charge;
If “B” has more e- than A, then B is somewhat (-), A must be somewhat (+); has a dipole
.4 to 1.7

10. Case #3 Electrons transferred completely (almost) – Ionic bond
A gives the e- to B; complete transfer of e-; whole # charges, NO δ;

12. B. Molecular polarity
Is the entire molecule polar?
If a molecule has nonpolar bonds, the molecule must be nonpolar overall.
If a molecule has polar bonds, the entire molecule can be either polar or nonpolar, depending on the geometry.

13. Examples: consider water and carbon dioxide.
The C – O bond is polar as is the O – H bond
Line Test – can you draw a single straight line separating the (+) and (-) charges?
yes – the molecule is polar
no – the molecule is nonpolar;

14. O
O = C = O H H
(nonpolar) (polar)