Warm Up #20 Define electronegativity. Which element is the most electronegative? Why is this element the most E.N.? Put these elements in order from least to most E.N. I, Cl, Br, S, H, P, O, F, N,C, ** hint- “brownies” Ability of an atom to attract electrons towards itself in a chemical bond Nitrogen Nitrogen has the most number of protons to attract another element’s valence e- with the fewest electrons of its own shielding those protons F > O > Cl,N > Br > C,S,I > H,P

Electronegativity

Electronegativity Ability of an atom to attract electrons towards itself in a chemical bond

Most electronegative element! Trend Most electronegative element!

F > O > Cl,N > Br > C,S,I > H,P Cause She Is a Hungry Person Frank Owes Claire Nine Brownies Put a comma in every third element These elements separated by commas are equal in electronegativity Memorize these!!!

Covalent Bond nonpolar polar H—H H—F equal sharing of electrons Electron density is symmetrical Unequal sharing of electrons Greater electron density near one element H—H electron poor region electron rich region H—F

e- poor e- rich BONDS, NOT MOLECULE!!! F H d+ d-

Polyatomic molecules Nonpolar Polar

Bond moments and resultant dipole moments in NH3 and NF3.

Partial charges, also known as dipoles, in the covalent molecules The whole crossed arrow shows the shift in the electron density. It points towards the more electron rich region (more electronegative element.) The “plus” end shows the electron poor region (less electronegative element.)

Partial charges, also known as dipoles, in the covalent molecules The delta (greek letter) also shows the shift in the electron density. Delta “negative” is the more electron rich region (more electronegative element.) The delta “plus” shows the electron poor region (less electronegative element.) d- d+ d- d- d- d+ d-

For each bond, indicate the shift (or pull) in the electron density.

Classification of bonds by difference in electronegativity Increasing difference in electronegativity Bond Type Covalent share e- Polar Covalent partial transfer of e- Ionic transfer e- 0 < and <2  2 Difference

F > O > Cl, N > Br > C, S, I > H, P Trend Most electronegative element!

Practice In each pair of bonds, put a (*) next to the more polar bond using your worksheet numbers and use an arrow (+) to show the direction of the polarity in each bond. H—S and B—C N—N and N—H   * 2.5-2.1=0.4, 2.5-2.0=0.5  * 3.0-3.0=0, 3.0-2.1=0.9