Chem Quix #4 Flashcards
Octet Rule Exceptions
1) Odd e- molecules
2) Hypovalent (e- deficient molecules)
3) Hypervalent molecules (valence shell expansion)
Odd e- molecules
Moleulce w/ odd e- can’t have octet for every atom
ex. NO w/ 11 valence e- or NO2 w/ 17 valence e-
Hypovalent Molecules
atoms w/ less then octet configuration
ex. BH3 & BF3
Hypervalent Molecules/Valence Expansion
molecules APPEAR to have atoms w/ more then octet of e- in valence shells but it’s maintained
ex. XeF2 (8e- + 2e- = 10e-) or PF5 (5+5=10e-) or SF6 (6+6=12)
Formal Charge
charge on atom in molecule if e- pair bonds are hypothetically broken (homolyticially)
Heterolytically
breaking covalent bond so e- pair is transferred to 1 of the partners (usually more electron(-)…resulting charges = oxidation states
2 extremes of formal assignment of bonding e- pairs
formal charge & oxidation states
Diff. between formal charge & oxidation #
FC = assuming equal sharing of e- VS Ox. # =assuming interaction is 100% ionic (transfer)
Neither FC or Ox # describe _____________ & actual charge is _____________
Neither FC or Ox # describe bonding in HETERNUCLEAR DIATOMIC MOLECULES & actual charge is INTERMEDIATE
Rules for Ox. #s
1) must add up to molecule charge
2) is always 0 in elemental form
3) nonmetals have (-) Ox. #s
Ox. # Rule Exceptions
1) Oxygen has Ox. # of -2 EXCEPT when combined w/ Flourine
2) Oxygen has Ox. # of -2 EXCEPT when combined w/ O-O bond
3) Ox. # of Hydrogen is +1 w/ nonmetals (EXCEPT B or Si)and -1 when bonded w/ metals
sum Ox. #s =
charge on molecule
VESPR
don’t account for lone pairs (repulsion between e- lone pairs is minimized)
In Ox. #s 1 valence e- pair =
- 1 single bond
- 1 double bond
- 1 triple bond
- 1 lone pair
Steric #
atoms bonded
(coordination # + lone pair #)
explain AXE notation
A: just is
X: coordination #
E: lone pair #
When is compound usually expressed w/ VESPR?
when X + E = steric #
Lone Pair Size & effects
larger than bond pair & thus repulsions are greater resulting in decreasing bond angle
Molecules w/ steric #5
Trigonal Bipyramidal (AX4E)
Trigonal Bipyramidal sites for lone pairs
axial & equatorial
Trigonal Bipyramidal isomers
has 2 depending on if lone pairs occupy axial or equatorial sites
Trigonal Bipyramidal preferred bonding site
equatorial (more spacious w/ 2 90 angles instead of 3 90 angles)
Octahedral preferred bonding site
sites separated by 180
Which is the most dominant & why?
lone pair-lone pair
lone pair-bond pair
bond pair-bond pair
lone pair-lone pair since they are closest to the central atom
Molecular Orbital Theory
account for lone pairs
e- moving in circular orbit will
lose its energy and spiral into the nucleus
What will an electric charge that undergoes acceleration (changes in velocity & direction) emit?
electromagnetic radiation & will lose energy w/ every turn
Synchrotron
beam of e- spinning & changes path to emit radiation
Quantization
examines radiation emitted from materials
Light
wave, particle, or energy
most electronic structure of atoms comes from analysis of
light emitted/absorbed by substances
Newton’s light discovery
light can be broken down into components w/ diff. color from red to violet w/ prism (ROYGBIV)
Wave lengths from longest to shortest (lowest frequency to highest)(lowest energy to highest)
Radio Waves
Microwaves
Infrared Radiation
(ROY G BIV)
Ultraviolet
Gamma Rays
Cosmic Radiation
3 Features of a Wave
1) Amplitude
2) Wavelength
3) Frequency
Wave Amplitude
max displacement (height above midline)
Wave Intensity
determines radiation levels (amplitude^2)
Wave Wavelength
peak-peak distance
Wave Frequency
wavelengths that pass through a given point in 1 second
1/s =
Hz
Speed eq.
distance frequency x wavelength
————- = ————————————
time 1
Distance eq.
frequency x wavelength
Sqeed eq. expanded
C in relation to frequency & wavelength
C = wavelength x frequency
Speed of Light in a vacuum (c)
3x10^8
- will have diff. speeds in diff. medians but never faster
Frequency in relation to C & wavelength
Frequency = c/wavelength
High Frequency has ____________ wavelength & ___________ energy?
Short wavelength
High Energy
ex. red light
Low frequency has ____________ wavelength & ___________ energy?
Long wavelength
Low Energy
ex. violet light
Node
where magnetic field & electric filed intersect at 0
light electromagnetic radiation
oscillating electric & magnetic field perpendicular to direction in which the light is propagating
Electric fields exert an influence on
particle changes
Magnetic fields exert an influence on
moving charged particles
Electromagnetic
has large range of wavelength & frequencies w/ no limit
Red light
Low frequency
Long wavelength
Ultraviolet light
High frequency
Short wavelength
Infrared light
corresponds to the heat we feel from a hot object
What did black body radiation, photoelectric effect, & atomic spectra prove?
Objects can’t lose or gain energy in arbitrary or continuous amounts
Explain Black Body Radiation Experiment
put _______ into black body and w/ it bouncing off…examined color shift of BBR & demonstrated that the wavelength corresponds to the mas is INVERSELY proportional to the temp.
ex. of red hot and white hot heat
red hot = stove top burning
white hot = incandescent bulb
Black body radiation is a function of
temp. & total intensity over all wavelengths is proportional to the power of temp.
max @ 1000K is shorter then that for
800K
Photons in a black box as an analogy for Oscillators
Black box
box that absorbs all photons incident upon it & re-radiates the photons till they reach thermal equilibrium
Ultraviolet Catastrophe
Any object @ non-zero temp. would emit intense ultraviolet radiation (even X-Rays) & would devastate the countryside
- Breaks law of conservation of energy
Rayliegh’s results
black body should emit an infinite amount of energy (breaks law of conservation of energy)
moles per unit frequency per unity volume eq.
8piv^2/c^3
increased frequencies you can fit _________ modes into the cavity
more because shorter wave lengths (2x frequency = 4x modes)
Basis for Classical Calculations
radiated photons (electromagnetic waves) can be considered to be produced by standing waves (resonant modes) in the cavity which is radiating
Standing waves
resonant modes
radiated photons
electromagnetic waves
BBR Classical Theory
intensity INCREASES as frequency INCREASES
- that matter can absorb/emit any energy quantity
- didn’t predict region
BBR Experimental Results
max value of inensity exists as a function of wavelength
What would happen to humans in ultraviolet catastrophe?
Our bodies would glow in the dark but there wouldn’t be any darkness to glow in
How must an oscillator gain & lose energy?
In quanta of magnitude h x frequency where H is plank’s constant
Plank’s Constant
6.63x10^-34 J s
Classical Oscillator
has CONTINUOUS values of energy and can gain or lose energy in arbitrary amounts (ramp)
Quantum Oscillator
has DISCRETE energy levels & can only gain & lose energy in discrete amounts (steps that can’t be climbed if not enough energy to reach next level)
Low frequency oscillators have (occupied or unoccupied) levels?
Occupied energy levels
High frequency oscillators have (occupied or unoccupied) levels?
Unoccupied energy levels
What eq. shows radiation of frequency from oscillating atom releasing energy into its surroundings?
Frequency = energy / h
What is intensity of radiation?
energy packets generated by ind______
- measured in energy
Planks Hypothesis
radiation of frequency can only be generated if enough energy is available since atoms of a cool body don’t have enough energy to generate a high frequency UV radiation (ultraV. cat. is avoided)
Planks Law
deltaE:
n:
h:
v:
hv:
deltaE = nhv
n: integer #
h: 6.63x10^-34
v: radiation frequency
hv: energy quanta
Photoelectric Cell (photocell) experiments by H. Hertz
ultraviolet radiation strikes a metal surface in vacuum & the ejected e- are attracted to (+) charged collector & a current flows
Photoelectric Effect Observations
1) max kinetic energy of e_ doesn’t increase as intensity of light increases (more e- emitted)
2) no e- emitted unless radiation has frequency above threshold value characteristic of that meta
3) e- ejected immediately regardless of how low intensity of radiation
4) kinetic energy of ejected e- increase linearly w/ frequency of incident radiation
Red light shown onto metal:
Low intensity purple light on metal:
High intensity purple light on metal:
Red: frequency too low, no e- ejected from metal & no electric current flows
Low purple: above threshold frequency so SOME e- ejected from metal; small current
High purple: above threshold frequency so MANY e- ejected from metal; high current
Einstein said electromagnetic radiation consists of ___________?
Particles (photons)
E=h x frequency
Photon
packets of energy related to frequency
Do photons of blue light or red light have higher energy?
Blue light photons
When energy of photon less the threshold, how does intensity effect e- ejection?
It doesn’t…almost or far away are both not THERE
When energy of photons is more than threshold, what is excess energy and how does it effect ejected e-?
appears as Kinetic energy of the ejected e-
How does light eject e- from metal?
When light (photon particles) strikes metal, the energy is transferred to e-. If energy to e- is sufficient, it’ll overcome the attractive forces & e- will be ejected.
How does light frequency effect photoelectron kinetic energy?
Linearly after threshold
How does light intensity effect photoelectron kinetic energy?
It’s a constant
Work Function
barrier that e- must overcome to escape from surface (initial hv)
Kinetic Energy eq.
KE = hv - work function (initial hv)
- intercept (work function) depends on metal but slope (h) is constant
hv in terms of KE & work function
hv = KE + work function
Kinetic energy of e-
.5m(sub e) v^2 + (initial hv)
E in terms of h and frequency
E = h/frequency
