Home > Chemistry > Chemistry 1A Part Deux: Lecture 36 Notes

Chemistry 1A Part Deux: Lecture 36 Notes

Overview

As mentioned, I am doubling up this series to finish it off.  This is a 50 minute lecture on quantum mechanics (QM).  Unusually, they dump QM at the end.  Nietzsche put it in the beginning if I recall.

Details

With electrons hitting an object, you must concern yourself with the energy of each photon and the number of photons.

More positive charge in the nucleus affects orbital energy levels.  All transition metals have the oxidation state of +2, which comes from the 4s.

Very small objects confined to small spaces do not behave like massive objects in large spaces.  In other words, our ideas about macroscopic observations do not apply to electrons.

She outsources 10 minutes of her presentation to a cartoon character, Dr Quantum.

Heisenberg Uncertainty Principle (HUP)

d(mv) dx >=h/4pi

mv electron = h/wavelength

The more precisely the position is determined, the less precisely the momentum is known.

This is the nature of the system, not a limitation of the researcher.

Fix  the wavelength, location is unknown.  Fix the location, momentum is unknown.

Cloud Model of the Atom

A wave equation is used to obtain the probability of finding each electron in an atom.

Trident (xyz) is the wavefunction of the electron, trident ^2 is the probability of finding the electron.

Standing Waves

n=principle quantum number      number of  nodes      wavelength (w = 2L/n)

4                                                                     3                                   L/2

3                                                                     2                                2L/3

2                                                                     1                                  L

1                                                                       0                                 2L

E = hf

Only certain energies are allowed.  This is the one dimensional particle in a box.

The wave equation is a mathematic description of the amplitude of the electron wave.  The square is the probability.  The energy is related to the number of nodes and on L.

Trident (x,t) = (sqrt (2/L)) sin((n pi x)/L)

E n = (n2h2)/8mL2

Standing Waves in 3D

Spheres mark the 90% probability of finding an electron.  The size of the 1s orbital is ao = 52.9 picometers aka the Bohr radius.

p orbitals are dumbbell shaped, px/py/pz.  Each orbital holds two electrons.1 planar nodes.

5 d orbitals.  3 d orbitals have two planar nodes.  d zx/d yz/d xy/ dz2 / dx2-y2

The first quantum number defines the shell, the average radius (n = 1 2 3…)

The second quantum number defines the shape of the subshell (s p d f)

The third quantum number defines the orientation of the subshell (px py pz…)

How many nodes does a 5 f orbital have?

The pattern is n-1 so the answer is 4 nodes.

The fourth quantum number is electron spin.  Two electrons go into every orbital.  The electrons spin in opposite directions.  This is spin up 1/2 or spin down 1/2.

…this leads to an orbtial energy diagram

3px 3py 3pz

3s

2px 2py 2pz

2s

1s

Electrons spread out among orbitals of the same energy to maximize the parallel spins.  Each electron may be described by a unique set of 4 quantum numbers of shell, subshell, orientation and spin.

Review

Noble gases: He, Ne, Ar, Kr, Xe, Rd

Types of bonding: ionic >1.7, polar covalent between, non polar <0.5

PV = nRT

METT TC mission enemy troops terrain time civilians

SALUTE size activity location unit time equipment

2s 6p 10d 14p

KE electron = E photon – Ionization Energy

Tissue: epithelial, connective, nervous, muscular

Epithelial: simple/stratified/pseudostratified    cuboidal/columnar/squamous

  • single covalent bond – 1 shared pair
  • double covalent bond – 2 shared pairs
  • triple covalent bond – 3 shared pairs

Bond energy: single < double < triple

Bond length: single < double < triple

pKa’s:

Alkanes (50)

CH4/CH3-

Alkene (44)

Alkyne (25

HF +3.2

HCl -7

HBr  -9

HI -10 NH3 38 L

RCOOH (4-5)

HF (3.2)

NH4+ (9.26)

H2O (15.7)

ROH (17)

RSH (11)

H30+  (-1.7)

pKa = – log Ka

Spectroscopy: emission/absorption

A = e l c

IGL: point source, random motion, elastic collisions, high temp, low pressure

6 strong acids:

  • HCl
  • H2SO4
  • HNO3
  • HClO4
  • HBr
  • HI

The stronger the acid, the higher the Ka, the weaker the conjugate base.

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