chem 120
What's an isotope?
Atoms that have the same number of protons but a different number of neutrons
What's an allotrope?
different molecular forms of the same element
S2, S8, and S20 are all examples of what?
allotropes of S
what is atomic number?
equal to the number of protons in the nucleus of any of its atoms
how does a mass spectrometer work?
It operates on the principle that an atom or molecule, once ionized, can be deflected by a magnetic field. The amount that it's deflected depends on the speed of the particle, the strength of the magnetic field, and the mass-to-charge ratio
what's a mass spectrum
a graph of intensity versus the mass-to-charge ratio
relative abundances
one isotope more abundant than the other
average atomic mass
weighted average of the masses
atomic mass interval
used for certain elements to indicate the range of values expected for the atomic mass because of observed variations in the isotopic abundances of these elements. [a,b] form, >=a <=b
conventional atomic mass
the mass you use when you need a representative value when given a range of masses
synthesis
a+b->ab, two or more come together
decomposition
ab->a+b, one reactant breaks down into two or more simple reagents
single displacement
ab+c->cb+a, one element is replaced by another more reactive element (eg. redox)
double displacement
ab+cd -> ad+cb, pos or neg ions of two ionic compounds replace each other (eg. ppte)
combustion
A compound reacts with an oxidant (usually oxygen) in a highly exothermic reaction. For hydrocarbons, the products are carbon dioxide and water.
Acid-Base
A proton is transferred from a proton donor (acid) to a proton acceptor (base).
proton donor
acid
proton acceptor
base
solution
homogeneous mixture of one or more solutes in a solvent
homogeneous
uniform composition, right down to the molecular level; the molecules of one substance are mixed uniformly amongst the molecules of the others
solvent
determines the phase of the solution (i.e., solid, liquid, or gas); usually the most abundant component
solutes
all other components of the solution
aqueous solns
Aqueous solutions have water as solvent
comprised of positive and negative ions
ionic compounds
arranged in regular, repeating patterns
ionic compounds
the ions are held in their positions by strong bonding forces
ionic compounds
typically solids at room temperature
ionic compounds
when this type of solid dissolves in water, positive and negative ions break away from the solid surface and become “hydrated”
ionic compounds
dissociate not dissolve (creates ions in a soln)
ionic compounds
comprised of stable, neutral molecules
molecular compounds
the compound may be solid, liquid or gas at room temperature depending on the strength of the intermolecular attractions
molecular compounds
typically dissolves not dissociates, molecules become hydrated in water
molecular compounds
precipitate
insoluble solid formed from the solution
proton transferred from _____ to ________ in lowrey bronsted acid base rxns
acid to base
hydrochloric acid
strong
HBr hydrobromic acid
strong
HI hydroiodic acid
strong
HClO4 perchloric acid
strong
HBrO4 perbromic acid
strong
HIO4 periodic acid
strong
H2SO4 sulfuric acid
strong, diprotic
HNO3 nitric acid
strong
group 1 hydroxides: LiOH, NaOH, KOH, RbOH
strong bases
group 2 hydroxides: Mg(OH)2, Ca(OH)2, Sr(OH)2, Ba(OH)2
strong bases
When do neutralization reactions essentially go to
completion
If either the acid or the base is “strong”
What do acid-base neutralization rxns typically produce?
salt & water (water often but not always)
theo yield
max amount of product that can be produced
limiting reagent/reactant
the species that limits the amounts of product that can form (runs out first)
consecutive rxns
a series of reactions that occur sequentially; the products from one reaction are consumed as reactants in a subsequent reaction (can add)
t or f: can add together consec rxns
true
t or f: can add together simultaineous rxns
false
simultaneous rxns
reactions that are independent and occur at the same time
another name for simultaneous rxn
independant
green chemistry
an approach to chemistry that is intentionally focused on not only the efficient use of atoms (and energy) but also chemical methods that reduce or eliminate reagents, products, solvents, by-products, wastes, etc. that are hazardous to human health or the environment.
atom economy
defined in terms of the theoretical amounts of reactants and products involved in a reaction or process (is a percentage)
% atom economy eqn
(stoic mass of desired prod (only) / mass of a stoichiometric mixture of reactants) x 100%
stoichiometric mass
the maximum mass that can be expected from a stoichiometric mixture of reactants
stoichiometric mixture
the mole ratio of reactants is equal to the ratio of the stoichiometric coefficients. None of the reactants is present in excess.
higher atom economy is better or worse?
better, we want higher percent atom economy
e-factor/environmental factor
quantity that can be calculated by a chemist to help assess the “green-ness” of a chemical reaction or process, defined in terms of quantities that are easily measured
e-factor eqn
mass of waste produced / mass of product obtained
does water count as a waste product when calculating e-factor?
no
bigger or smaller e-factor is better?
small. A large value for the E-factor indicates that many kilograms of waste are generated for every kilogram of product obtained. A small value for the E-factor is desirable
what is this called: When an electron is “confined” to a finite region of space by the forces exerted on it, its total energy is restricted to certain special values!
quantization
what does light being em radiation that transmits energy through space or some other medium mean?
Light has an electric field that oscillates at a certain frequency, and a magnetic field that oscillates at the same frequency, perpendicular to the plane of the electric field
how is em radiation produced?
when electrical charges (e.g. electrons) undergo some sort of
acceleration
Wavelength
distance between successive maxima (m)
period (T)
time it takes for the electric field to return to its maximum strength (s)
frequency
# of times per second the electric field reaches its maximum value, (s^-1), inverse of period
t or f: gamma rays have more energy than x-rays
t
t or f: gamma rays have more energy than radio waves
t
t or f: gamma rays have a higher frequency than radio waves
t
t or f: gamma rays have a larger wavelength than radio waves
f
starting from largest wavelength and going towards smallest wavelength (highest freq), what comes after radio waves?
microwaves
starting from largest wavelength and going towards smallest wavelength (highest freq), what comes after microwaves?
infrared
starting from largest wavelength and going towards smallest wavelength (highest freq), what comes after infrared?
vis light (roy g biv)
starting from largest wavelength and going towards smallest wavelength (highest freq), what comes after visible light?
ultraviolet
starting from largest wavelength and going towards smallest wavelength (highest freq), what comes after ultraviolet?
x rays
starting from largest wavelength and going towards smallest wavelength (highest freq), what comes after x rays?
gamma rays
visible light region
about 400nm-750nm
What is blackbody radiation?
Regardless of composition, an object at 300 K will emit light in the mid-IR region. (Atoms in a heated solid oscillate with certain energies only)
The Photoelectric Effect
photoelectric effect, light is used to dislodge electrons from the surface of a metal
three things learned from photoelectric effect
1. electrons were ejected only if the frequency of light was greater than some “threshold” frequency
2. kinetic energy of e- increased proportionally w frequency for frequencies greater than threshold frequency
3. electrons were ejected instantaneously (no observable time delay) regardless of the intensity of the incoming light
work function
the minimum energy required to dislodge an electron from the metal’s surface
Line spectra of atoms
The emission spectrum of any substance can be obtained by energizing the sample of material. prisims split white light so place atomic gas sample btwn. will create dark lines showing quanta of energy were absorbed by the atomic gas. Alternatively, if the light emitted from a sample of high energy atoms is dispersed into its component wavelengths, only certain colours of lines appear. (absorption or emission spectrum created showing the quantization of energy)
what experiment showed the energy of light is highly localized and proportional to it's frequency?
photoelectric effect
who did the photoelectric effect
einstein
who did blackbody radiation
planck
key takeaway from line spectra & atoms
The energy of an electron in an atom is not arbitrary, but rather, it is restricted to have certain “special” values
radius of 1s orbital, Bohr radius
52.9 pm
why are all energies negative for energy level diagram of H atom
E = 0 when e- is infinitely far away (from nucleus). If dist decr, eng does too... therefore it's neg for all dist other than infinitely far away
as n -> infinity (aka 7...)
dist btwn energy levels -> 0 (less space between eng lvls as n gets larger)
When the electron “drops” from a higher energy level (Eupper) to a lower energy level (Elower), the atom emits a photon with energy equal to ________
Eupper − Elower
In order for the electron to “jump” from a lower energy level to a higher energy level, the atom must absorb a photon with energy equal to _________
Eupper − Elower
what were the 3 problems w bohrs model for the H atom
1. cannot extend it to other atoms
2. doesn't explain why H doesn't emit radiation conti
3. doesn't actually explain WHY the ang mom is quantized, just knows that is HAS TO BE (conditions were imposed)
what was de brog's hypoth that helped describe behaviour of e- in atoms?
wave-aprticle duality
what was heisenberg's principle that helped describe behaviour of e- in atoms?
Heisenberg uncertainty principle (can never know true behaviour of a system)
Diffraction suggests light behaves as a _____
wave
The photoelectric effect suggests light behaves as _______
particles
diffraction
when light passes through a hole or slit whose size is comparable to the wavelength of the light (con & des int. of waves make diffraction patterns)