Module 7 (Part II)

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

\-

4 electron groups

0 lone pairs

\-tetrahedral

\-109.5 degrees

4 electron groups

1 lone pair

\-trigonal pyramid

\-

4 electron groups

2 lone pairs

\-bent

\-

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