Unit 6 quantum mechanics molecular s tructure and orbital theory
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Unit 6 : Quantum Mechanics, Molecular S tructure, and Orbital theory. By: Eddie Yokana a nd Jake Gold. Molecular Geometries. Note double and triple bonds are counted as ONE electron domain. Electrons will always situate themselves to minimize repulsion. Polarity.

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Unit 6 quantum mechanics molecular s tructure and orbital theory

Unit 6: Quantum Mechanics, Molecular Structure, and Orbital theory

By: Eddie Yokana


Jake Gold

Molecular geometries
Molecular Geometries

  • Note double and triple bonds are counted as ONE electron domain.

  • Electrons will always situate themselves to minimize repulsion.


  • 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, trigonalbipyramidal, 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
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.


  • 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 10-34and 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 10-34Kg.

  • λ= h/(mv)

    • is the de Broglie wavelength.

Molecule orbital energy levels
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

Lewis Electron-Dot Example


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






6(4)e-= 24 e- needed

26e- > 24 e-

  • Sum up valence electrons

  • Make a basic single bond skeleton

  • Determine electrons remaining (subtract those used in bonds)

  • Determine electrons needed to complete octets

  • Remain = needed : Finished

  • Remain > needed : extra lone pair(s) on central atom

  • Remain < needed : add extra pi bond for every 2 electron deficit






Lewis dot structure continued
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










Periodic Trends

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

Increasing Atomic Radius (size)

Increasing Electronegativity

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.

Increasing Atomic Radius (size)

Increasing Electronegativity

  • Note:

  • As Electronegativity INCREASES, atomic radius DECREASES

  • (Except Noble Gases)*Remember effective nuclear charge increases going across and orbitals are added going down

Electron Orbitals

“s” Block

“p” block

“d” Block

“f” Block


Electron Configuration

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

Orbital box Notation:

3 Ways of writing electron configurations:

Orbital box Notation

Spectroscopic Notation

Shortcut Notation

  • Spectroscopic Notation:

Noble gas core Notation:

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

  • 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,fusing the numbers 0,1,2,3 respectively)

  • mldescribes the specific orbital within the subshell (For d’s subshell it goes -2,-1,0,1,2)

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

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

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

  • “Low Energy to High Energy=Order of Filling”