Jan 2025 final exam - from my paper notes Flashcards
orbital
a wave function describing the probability of finding an electron in a certain place
hybrid orbital
multiple orbitals overlapping - constructive/destructive interference
geometry for first 5 hybridizations
sp - linear
sp2 - trigonal planar
sp3 - tetrahedral
sp3d - trigonal bipyramidal
sp3d2 - octahedral
formal charge formula
FC = #valence electrons - #non-bonding valence electrons - (#bonding electrons)/2
(valence e- - number of electrons IN lone pairs - electrons in bonds/2)
how to find optimal lewis dot structure with formal charge?
- Find the formal charge of each atom in each of the possibl arrangements
- You want the sum of the absolute values of all the formal charges to be equal to the overall charge of the molecule/ion
- If more than one arrangement has the same sum of formal charge absolute values, we also want all of them to have a FC of 0 if possible, or as close to 0 as possible, and if none of those are possible the more electronegative elements should have the most negative FC
Bonding steps (lewis dot diagram)
- choose central atom - least electronegative, greatest bonding potential, often highest z, group others around it
- count total # of valence electrons (all atoms+ionic charge)
- a sigma bond (1 electron pair) between each atom and the central atom
- fill in all the lone pairs (octet rule)
- add a pi bond if central atom’s octet isn’t full
- any remaining electrons: add as lone pairs on central atom
- use FC to determine the best option if multiple work
bond order for normal bonds (easy)
1 for single,2 for double, etc
bond order for structures with resonance
- if there is a sigma bond on each side, start with order 1 (doesn’t matter how many sigma bonds)
- then, look at how many bonds your remaining electron pair is split over. Ex. in ozone, one pair over 2 bonds. in carbonate, 1 pair over 3 bonds. then add: 1/2 or 1/3 respectively, for 1.5 or 1.33 bond order
addition polymerization
unsaturated bond broken to form a chain, no by-products, addition reaction
addition polymerization mechanism
- initiation: X2 breaks into 2 halogan radicals (uv light or heat)
- Propogation: homolytic fission breaking double bond and halogen attaches to the organic molecule, making a radical
this radical reacts with another alkene to make a longer alkane radical chain, This keeps happening until 2 of these chains react - 2 radical chains react, ending the chain reaction and forming a polyalkene (with just a signle bond now) and the halogen on the end
condensation polymerisation
bi-functional monomers, condensation reaction, by-product produced
Asymetric electrophilic addition mechanism
- alkene and ex. HCl: Within HCl, H is positive dipole and is attracted to the alkene double bond (exposed pi-bonding electrons). HETEROlytic fission from the bond, hydrogen attaches to a carbon (major product: hydrogen goes to teh carbon with most hydrogens already on there. Chlorine anion formed as well as a carbocation on the 2nd degree carbon, and then they bond too. 2 possible products, one major one minor
nitration of benzene: how is nitronium formed?
HNO3 + S2SO4 —-> H2O + NO2+ + HSO4-
organic molecules: lower boiling point
- more branched
- shorter chain
- no hydrogen bonding
negative enthalpy
exothermic
bond enthalpy definition
energy required to break 1 mol of chemical bonds in the gaseous state, endothermic (AVERAGED across the same bonds in similar compounds)
reaction enthalpy using bond enthalpy
sum of broken - sum of formed
standard enthalpy of combustion definition
energy released when 1 mol of a substance in its standard state is completely burned with oxygen (exothermic)
standard enthalpy of formation definition
energy required to make 1 mol of a compound from its constituent elements in their standard states (endothermic)
born haber cycle - if you go clockwise, which arrows are facing the opposite direction (which signs do you flip?)
lattice enthalpy and enthalpy of formation
lattice enthalpy definition
energy required when 1 mol of a solid ionic compound is formed from its gaseous ions (endothermic)
order of born haber cycle things
formation enthalpy of the compound (standard state elements to compound), enthalpy of atomization of the mental (standard state to gas), n*bond enthalpy of the nonmetal (to break the bond so that there is 1 mol of a single gaseous atom), first (and sometimes 2nd) IE of the metal, EA of the nonmetal (now you have 2 gaseous ions), lattice enthalpy
how to do calculations w born haber cycle
go clockwise, add them all up (or subtract if arrow is reversed)
excess, somewhat limited, limited oxygen: combustion of organic compounds products
CO2+H2O, CO+H2O, C+H2O (always gaseous water)
fossil fuels
- highly exothermic and naturally abundant, but bad for environment bc produce greenhouse gasses (absorb IR radiation, hold on to thermal energy)
bio fuels
- renewable - burning of biomass (ex. plants) which already make glucose through photosynthesis
fuel cells
chemical energy to electrical energy using spontaneous exothermic reactions
entropy change of a reaction
sum of standard entropies of products - reactants
k (equilibrium constant)
[C]^c[D]^d/[A]^a[B]^b (lowercase are their stoic coeff.
K for a spontaneous forward reaction (products favoured @eq)
greater than 1 (and G is less than 0)
determining LR
- find n of each reactant using M and m
- divide it by its coefficient, lowest number is the LR
- REMEMBER to use n, not the divided number, in any further calculations
atom economy formula
molar mass of desired product / molar mass of all reactants
rates definition
change in concentration of reactants or products / time
collision theory
for reactions to occur, particles must collide with enough energy to overcome the Ea and with the correct geometry