Module 7 (Part II)

VSEPR Model

VSEPR Model

-Valence Shell Electron Pair Repulsion model

-based on arrangement that MINIMIZES REPULSION of shared & unshared electron pairs around central atom

-bond angles & unshared electron pairs help determine shape of molecule

-shared electron pairs are pushed slightly together by lone pairs b/c lone pairs contribute to repulsion

-electron pairs are located in a molecule as far apart as they can be

bond angle

-electron pairs repel each other and cause molecules to be in fixed positions relative to each other

-angle formed by 2 terminal atoms w/ central atom is called bond angle

2 electron groups

0 lone pairs

-linear

-180 degrees

3 electron groups

0 lone pairs

-trigonal planar

-120 degrees

3 electron groups

1 lone pair

-bent

- <120 degrees

4 electron groups

0 lone pairs

-tetrahedral

-109.5 degrees

4 electron groups

1 lone pair

-trigonal pyramid

- <109.5 (around 107 degrees)

4 electron groups

2 lone pairs

-bent

- <109.5 (around 105 degrees)

electronegativity & bond character

-equal sharing of electrons results in nonpolar covalent bond

-unequal sharing of electrons results in polar covalent bond

-bonding is often not clearly ionic or covalent

-the greater the electronegativity difference → the greater the ionic character

polar covalent bonds

-electrons spend more time around more electronegative atom

-results in partial charges at the ends of the bond

nonpolar covalent bond

-between 2 identical or very similar atoms

-not great electronegativity difference

-electrons shared equally & charge is balanced evenly

determining bond character according to EN difference

- > 1.7 = mostly ionic

- 0.4 - 1.7 = polar covalent

- < 0.4 mostly covalent

- 0 nonpolar covalent

polar molecules

-molecules are polar when electrons are shared unequally btwn atoms (contain polar bonds)

-this causes molecule to have partial neg charge on part of atom w/ more electrons (more electroneg atom)

-non-polar molecules aren’t attracted by an electric field

-polar molecules align w/ an electric field & are called dipoles

organic compound exceptions

-all carbon-containing compounds

-EXCEPTIONS:

-carbon oxides (ex. CO2)

-carbonides (carbon + a metal)

-carbonates (CaCO3)

organic compound structure

-carbon nearly always shares its electrons & forms 4 covalent bonds

-in organic compounds, carbon usually bonded to H or elements near carbon on periodic table (N, O, S, P, & halogens)

-bc C forms 4 bonds → forms complex, branched-chain structures, ring structures, & even cage-like structures

hydrocarbons

-simplet organic compounds

-contain ONLY elements C & H

saturated hydrocarbon

-contains only single bonds (ALKANES)

unsaturated hydrocarbon

-contains at least one double or triple bond (ALKENES & ALKYNES)

-watch names of alkenes & alkynes

-ex. (alkene example) 1-Butene → double bond is btwn 1st & 2nd carbon, but 2-Butene → double bond is btwn 2nd & 3rd carbon

alkanes

-one single bond btwn atoms

-simplest hydrocarbons

-name ends in -ane

-General formula: C(n)H(2n+2) where n=# of C

alkenes

-double covalent bonds btwn carbon atoms

-name ends in -ene

-for alkenes w/ only one double bond & 4 or more C, general formula: C(n)H(2n) where n=# of C

alkynes

-triple covalent bonds btwn carbon atoms

-name ends in -yne

-General formula: C(n)H(2n-2) where n=# of C