Chem exam 3

Pure covalent bonds/nonpolar

If atoms are identical or share electrons equally

Electrons have an equal probability of being near the nucleus

Strongest IMF always London dispersion forces

C-H bonds

Polar covalent bonds

Different atoms, bonding electrons not equally shared

Bonding electrons more attracted to one atom than the other= shift of electron density

partial positive charge on one atom and partial negative charge on the other

Strongest IMF is either Hydrogen bonding or dipole-dipole

Partial negative charge

Atom that attracts electrons more strongly - (the more electronegative atom)

Dipole moment

Measures bond polarity (arrow with the line pointing to most E.N atom

ex: Electrons pulled strongly toward one atom= large dipole moment

Electrons shared evenly= 0 dipole movement

Range for pure covalent/nonpolar range

0.0-0.4

Polar covalent range

0.5-1.7

Ionic range

1.7 and higher

Steps of determining a Lewis structure

1. count up valence electrons

2. draw the skeletal structure ( least E.N atom in center)

3. Complete octets of the terminal atoms

4. place any remaining electrons on the center atom

5. SOMETIMES NEEDED: if atoms are short their octet- make multiple bonds

what center atoms forms incomplete octets?

Be, Mg, B, Al

What center atoms form expanded octets?

group 3 and down

Resonance structure

one of two or more Lewis structures for a single molecule

Idea formal charge

FC of zero is the best

keep them small ideally + or minus one

Negative charge goes to MOST E.N. atom

Positive charge belongs to LEAST E.N. atom

DONT want central atoms to have large positive charges

hybridization

starting at 2 electron domains: sp, sp², Sp³, Sp³d, Sp²d²

Bond angles of tetrahedral

109.5

Bond angles of trigonal plane

120

Bond angles of linear

180

Bond angles of trigonal bipyramidal

120 and 90

Bond angles of octahedral

90

Weakest IMF

London dispersion forces- only forces found in non polar molecules- no dipoles

Strongest IMF

Hydrogen bonding

special case of dipole-dipole interaction

Least EN paired with most EN

What are the only 3 groups that give hydrogen bonding?

O-H, N-H, F-H

Dipole-dipole interactions

IMF found in polar molecules

if Hydrogen bonding doesn’t apply

cancel when all outer atoms are identical, the shape is symmetrical

when is a geometry polar?

Shape is not symmetric

Outer atoms not all identical

Lone pairs on central atom that break symmetry