metallic bond
bonds present in metals
- nuclei immersed in a sea of e-
- not important
types of bonds
(1) ionic bond
(2) covalent bond
(3) metallic bond
octect rule
atoms gain, lose or share e- to achieve full outershell octet of valence e-
ionic bond
opposing charged ions attract via electrostatic force
- greater charge, greater attraction
lattice energy (Eel)
energy of ionic bond
Eel = kQ1Q2/d
Q1 - positive ion charge
Q2 - negative ion charge
d - sum of ionic radii
lattice energy rules
(1) small = greater lattice energy, stronger attraction
(2) higher charge = greater lattice energy
(3) look at charges first, less is better
(4) if same charge, look at atomic radii (smaller = higher)
covalent bond
sharing of e- btwn similar elemental compounds
electronegativity
atom tendency to attract or pull e- towards it
- related to polarity
- higher bp = higher Zeff
- fluorine = greatest Zeff
terms describing polarity / bonds
a bond…
- is polar
- has dipole moment
- has a dipole
- is polarized
electronegativity rules
if difference equals
- 2 or more, ionic
- 1.9 - 0, polar covalent
- 0, nonpolar covalent
bond polarity
describes unequal e- sharing in a bond
- nonpolar covalent bond
- polar covalent bond
nonpolar covalent bond
e- shared equally btwn atoms
polar covalent bond
one atom exerts > attraction for e- than other
dipole
magnitude of dipole moment
- one end negative charge, other end positive charge
polarity
dipole moment
measure of separation & magnitude of +/- charges
- debyes (D)
- high charge = more
- more distance = more
resonance
case where 2 or more Lewis structures are equally good descriptions of a single molecule
- actual = average, hybrid or blend of resonance structures
exceptions to octet rule
(1) odd # e-
(2) < # e- of full octet
(3) > # e- of full octet
formal charge
method of assigning apparent charge to each atom in a Lewis structure
- used to determine which resonance structure is most likely to exist
steps to determine formal charge
(1) determine # valence e- for atom
(2) subtract # nonbonding e-
(3) subtract # bonds
formal charge rules
(1) formal charge close to/of 0 = favored
(2) formal charge of ±2 ≠ favored
(3) neg. charge tends to reside on electronegative atoms
oxianion
polyatomic ion containing O w/ neg. net charge
- may combine w/ cation to form an ionic compound
(ie) SO4, NO3 & CO3
bond length determined by
(1) bond order - single, double, triple, etc. bonds
(2) atoms involved
bond length rules
(1) less bond order, greater bond length
(2) less bond length, higher bond energy
(3) less bond length, less ∆H to break/make bond
estimating ∆Hrxn using bond energies
∆Hrxn = ∈ ∆H (bond breaking) + ∈ ∆H (bond making)