Executive Summary for Unit 6: Atomic and Molecular Structure. These
notes are meant to Guide your Studying, not to substitute for it!
Atomic and Electronic structure, quantum mechanics
1. Energy quantization-Smallest possible quantity of energy=Quantum.
2. Photoelectric effect-when light of sufficiently high energy strikes a metal, electrons
are ejected.
3. Wave/particle duality-All matter has wavelike and particle-like characteristics
4. DeBroglie wavelength-Use the kinetic energy of a particle to solve for its wavelength.
5. Quantum numbers-n, l, ml, ms
6. Electron configurations of atoms and ions-Use periodic table as guide. For ions,
always add/subtract from highest principle quantum number. Deviations from
predicted configuration could occur to minimize the number of paired electrons.
Periodic Trends
1. Atomic size-generally increases down a column, and decreases across a row
2. Ionic size-compared to its normal element, cations are smaller, anions are larger
3. First and subsequent ionization energies
4. Electronegativity-Electronegativity tends to increase up a column and across a row
5. Exceptions to these generalities often occur in the areas of the periodic table where
atoms are transitioning from having zero paired electrons to 1 paired electron. The
additional electron increases repulsions and decreases stability.
Molecular Structure
1. Covalent bonding- sharing of electrons
2. Lewis Structures- one dot per valence electron, - indicates a single bond, = a double
bond, ≡ a triple bond. If too many electrons, dump them on the central atom. If too
few electrons, utilize double or triple bonds.
3. Molecular shapes/bond angles- 5 basic: linear (2 domains, 180°), trig. planar(3
domains, 120°), tetrahedral(4 domains, 109.5°), trig bipyramidal(5 domains,180°
poles, 120° equatorial), octahedral(6 domains,180° poles, 90° equatorial). Not all
electron domains are bonding domains.
4. Bond order/bond length- Bond order = number of bonds. Bond length decreases as
bond order increases
5. Formal charge- way of “bookkeeping” electrons- subtract individual electrons and ½
of bond electrons from the atoms normal amount of valence electrons. Lowest formal
charge = best Lewis structure when multiple structures are possible.
6. Bond polarity/molecular polarity- Electronegativity difference >.4 = a polar bond.
Molecules are only polar if they have polar bonds, and nonsymmetrical shapes.
Bonding theory
1. Valence bond theory (hybrid orbitals)- helps better explain bonding. Hybridization
does not create orbitals, it substitutes. The orientation of the hybrid shells is
predictable by VSEPR
2. Sigma and pi bonds- The first bond is always a sigma (σ) bond. If there is a double or
triple bond, the 2nd/3rd bonds are pi (П) bonds.
3. Molecular orbital theory- bond order = ½(#bonding e- - #antbonding e-)
Equations/Constants
E=hf
KE=1/2mv2
c=fλ
λ= h/(mv)
8
-34
C= 2.9979x10 m/s
h=6.626x10 J•s
me=9.11x10-31 kg