Unit 6: Quantum Mechanics, Molecular

Structure, and Orbital theory

By: Eddie Yokanaand

Jake Gold

Molecular Geometries

– Note double and triple bonds are counted as ONE electron domain.– Electrons will always situate themselves to minimize repulsion.

Electron Domains

Molecule Names

Orbitals Hybridized

Bond Angles

Two electron domains

Linear sp 180°

Three electron domains

Triangular Planar, Bent

sp2 120°

Four electron domains

Tetrahedral, Trigonal

pyramidal, Bent

sp3 109.5°

Five electron domains

Trigonal bipyramidal,

Seesaw, T-shaped, linear

sp3d 120°, 90°

Six electron domains

Octahedral, Square

pyramidal, Square planar

sp3d2 90°

Polarity• A bond is polar with electronegativity difference 0.5 or greater on the Pauling scale.

– All ionic bonds are polar.– Fluorine and oxygen are polar with all atoms (besides itself).– Generally if more than two spaces apart on periodical table then polar.

• A molecule is polar if polar bonds are asymmetrical.– Naturally symmetrical molecules: linear, trigonal planar, tetrahedral, trigonal

bipyramidal, octahedral, and square pyramidal. • In a polar bond, the atom that originally had a higher electronegativity has a partial negative

charge (δ-), and the atom with the lower electronegativity has a partial positive charge (δ+).

Electromagnetic Radiation• There are six types of electromagnetic radiation: gamma rays, x-rays, visible light, infrared,

and radio waves (in increasing wavelength).• Visible light has wavelengths between 400nm to 700nm.

– Remember ROYGBIV- Red, Orange, Yellow, Green, blue, indigo, and violet (Order of light in decreasing wavelength.

Equations• Light (c) goes at the speed of 2.9979 X 108 m/s through space, but slightly slower in air and

about 1.5 times slower in water.• C=fλ

– this equation is the relationship between frequency (f) and wavelength (λ). • E=hf

– This equation solves for the energy (J) contained one photon. h is Plank’s constant, which is 6.626 X 10-34 and f is frequency.

• KE= energy of a photon - energy threshold.– The kinetic energy of an electron will equal the amount of energy hit by a photon minus

the amount of energy it takes to emit the electron.• KE= ½ mv2

– this equation can be used to solve for the velocity (v) of an electron if you know the kinetic energy (KE) of the electron. m is a constant, which is the mass of an electron, which is 9.11 X 10-34 Kg.

• λ= h/(mv) – is the de Broglie wavelength.

Molecule Orbital Energy Levels

• Bonding nodes- help form bond• anti-bonding nodes- break apart bond• Energy increases going up the chart• Net Sigma bonds = (# of binding

electrons in sigma bonds - # of anti-binding electrons in sigma bonds) / 2

• Net pi bonds = (# of binding electrons in pi bonds - # of anti-binding electrons in pi bonds) / 2

• Bond order = (# of bonding electrons - # of anti-bonding electrons) / 2 – Or = net sigma bonds + net pi

bonds

O2

1. Sum up valence electrons

2. Make a basic single bond skeleton

3. Determine electrons remaining (subtract those used in bonds)

4. Determine electrons needed to complete octets

o Remain = needed : Finishedo Remain > needed : extra

lone pair(s) on central atomo Remain < needed : add

extra pi bond for every 2 electron deficit

SF4

Lewis Electron-Dot ExampleSTEPS6e-

7(4)e-

6+28=34e-

S

F

F

F

F

34e- - 8e- = 26e- remaining

6(4)e- = 24 e- needed

26e- > 24 e-

Lewis Dot Structure continued• If multiple isomers for molecule, then molecule with least formal charges will be the most

stable. • If two structures have the same amount of formal charges, then the more electronegative

atom will form the bond.• If both atoms are the same, then it could be a resonance molecule. This a way of describing

delocalized electrons within a molecule

S OO

S OO

S OO

Periodic Trends

Increasing Electronegativity

Incr

easi

ng E

lect

rone

gativ

ity

Note:• As Electronegativity INCREASES, atomic radius DECREASES• (Except Noble Gases)

*Remember effective nuclear charge increases going across and orbitals are added going down

Increasing Atomic Radius (size)

Incr

easi

ng A

tom

ic R

adiu

s (s

ize)

*Unequal electron affinity (i.e. >0.5) leads to polar bonds but the polar bonds must be asymmetrical for a molecule to be polar

Electron affinity is the ability of an atom to attract electrons from a bond.

*Since noble gases do not bond with other elements naturally, they are not included as we consider electronegativity.

Electron Orbitals“s” Block

“d” Block

“p” block

“f” Block

Electron Configurationhttp://www.shs.d211.org/science/faculty/hlg/e%20conf%20travis/electron_configuration.htm

3 Ways of writing electron configurations:Orbital box Notation

Spectroscopic Notation Noble gas core Notation

*Note: The “d” orbitals and the “f” orbitals have different principle quantum numbers

Electron Configuration

3 Ways of writing electron configurations:Orbital box Notation

Spectroscopic NotationShortcut Notation

http://www.shs.d211.org/science/faculty/hlg/e%20conf%20travis/electron_configuration.htm

Orbital box Notation:

Spectroscopic Notation:

Noble gas core Notation:

Element Total Electrons Shortcut Notation

Molybdenum - Mo 42 [Kr] 5s14d5

Tin - Sn 50 [Kr] 5s2 4d105p2

Tungsten - W 74 [Xe] 6s2 4f14 5d4

Element Total Electrons Written Notation

Oxygen - O 8 1s22s22p4

Phosphorus - P 15 1s22s22p6

Quantum Numbers

• Four quantum numbers: n, l, ml, ms. • N is the principle quantum number, and it identifies the electron shell or energy level (begins

at 1). • l describes the subshell (s,p,d,f using the numbers 0,1,2,3 respectively)• ml describes the specific orbital within the subshell (For d’s subshell it goes -2,-1,0,1,2)

• ms describes the spin. The spin is either +1/2 or -1/2. If electron is the first to go in a specific orbital, ms is positive, and the second electron is negative.

• “Electron Density and Molecular Geometry” http://employees.csbsju.edu/hjakubowski/classes/ch123/Bonding/vsepr.gif

• “Low Energy to High Energy=Order of Filling” http://

www.chemistryland.com/CHM130W/10-ModernAtom/Spectra/ModernAtom.html

WORKS CITED

http://www.concord.org/~ddamelin/chemsite/d_bonding/configs.html

http://www.shs.d211.org/science/faculty/hlg/e%20conf%20travis/electron_configuration.htm