DAT Chemistry Ch. 3 Bonding and Chemical Interactions

complete transfer of e- from atom w/ smaller ionization energy to atom w/ greater ionization energy affinity, ions held together by electrostatic forces.

difference of electronegativity greater than 1.7

Group I/II + Group VII

high MP
high BP
conduct electricity in liquid & aq. states, not solid

ionic solids form from crystal lattices

sharing e- btw 2 or atoms with similar electronegativity.

energy req. to form ions is greater than the energy that would be released upon the formation of an ionic bond.

low MP
do not conduct electricity in liq or aq states.

# of shared e- pairs btw 2 atoms
1, 2, 3 e- pairs = single, double, or triple covalent bond.

1. Bond length: avg length btw 2 nuclei of atoms involved in bond
triple bond < double bond < single bond.

2. Bond energy: energy req to separate 2 bonded atoms

str of bond increase as # of shared e- pair increases.
triple bond > double bond > single bond.

shared valence e- of covalent bond

valence e- not involved in covalent bond

unshared e- pairs = lone e- pairs

-Lewis dot symbol
-least electronegative atom is central atom.
-count all valence e- of atoms

V = 1/2 Bonding electrons - non bonding electrons

A Lewis structure w/ small or no formal charge is preferred over a Lewis Structure w/ large large formal charge.

Lewis structure /w neg. formal charge place on more electronegative atom, more stable

Atoms found in or beyond 3rd period can have more than 8 valence e-, occupy d orbitals

occurs btw atoms with small differences 0.4 to 1.7 Pauling units

More electronegative atom is partially Negative

Less electronegative atom is partially positive

vector quantity cursive-m, defined as the product of the charge magnitude (q) and the distance btw 2 partial charges (r): cursive m = q*r
-denoted by arrow pointing from pos to neg charge measured by Debye units (coulomb-meters)

occurs btw atoms that have same electronegativity

nonpolar covalent bonds occur diatomic molecules H2, Cl2, O2, N2

share e- pair, from lone pair of one of atoms in molecule, typically found in Lewis acid-base compounds

compound that can (a)ccept e- pair to form covalent bond

F H
| |
ex: F--B + :N--H
| |
F H
Lewis acid Lewis base

compound that can donate an e- pair to form covalent bond

3-D arrangement of atoms surrounding central atom
-determine by repulsion btw bonding & nonbonding e- pairs
-e- pairs arrange themselves far apart as possible minimizing repulsion

180 degrees

AX_3 = 120 degrees

AX_4 = 109.5 degrees

AX_3E_1 < 109.5

..
|
A
/ | \
X X X

AX_5 = 90, 120, 180 degrees

X
x |
`A- x
/ |
x X

AX_4E > 90 degrees
< 120 degrees

..
x |
`A-x
/ |
x x

AX_6

AX_2E_1 < 120 degrees

AX_2E_2 < 109.5 degrees

-molecule w/ net dipole moment is polar
-molecule w/ nonpolar bonds is always nonpolar
-molecule w/ polar bonds may be polar or nonpolar depending on orientation of bonding dipoles
ex:

Cl
|
C
/ | \
Cl Cl Cl

+ + = bonding orbital

+ - = antibonding orbital

sigma bonds = orbitals overlap head to head

pi bonds = orbitals are parallel

dipole-dipole interactions
hydrogen bonding
dispersion forces

-orient (+) region of 1 molecule close to (-) region of another molecule
-attractive forces only effective close
-dipole-dipole present in solid & liquid, not gas
-polar increase BP

-Strong dipole-dipole
-can be either INTRA or INTERmolecular
-Increases BP, more energy to break H-Bond
-important in behavior of water, alcohols, amines, & carboxylic acids

-Present in all molecules

-bonding e- of covalent bond may be equally shared, but will be located randomly throughout the orbit
-Permit unequal sharing of e- causing rapid polarization and counter polarization of e- cloud & short lived dipole = London forces

-London forces = temporary attractive force from e- from 2 adjacent atoms occupy position that make the atoms form temporary dipoles a.k.a. induced dipole.
-generally weaker than other intermolecular forces
-works in close proximity btw atoms
-large molecules, e- are far from nucleus are relatively easy to polarize therefore posses greater dispersion forces