Chem 1331: EXAM 2
87 Cards in this Set
| Front | Back |
|---|---|
|
VSEPR
|
Valence shell electron repulsion; places the electrons around the central atom as far apart from each other as possible
|
|
Electron-group arrangement
|
The 3D geometric arrangement/shape that all bonding and nonbonding electrons occupy
|
|
Molecular shape
|
The 3D shape that only the bonded atoms occupy,, i.e. what the molecule looks like
|
|
Steric number
|
The sum m+n; the number of electron groups
-Bond order between A and X doesn't really matter
X counts as one electron group
|
|
Bond angle
|
Angle between bonded atoms with the central atom as the vertex
|
|
Molecular Polarity
|
An uneven distribution of charge over a whole molecule or large portion of it
|
|
Criteria for molecular polarity
|
1) Must have polar bonds (difference in EN is >0)
2) Individual bond dipoles must be asymmetrically distributed
|
|
For the molecular polarity table to work:
|
all X's must be the same
|
|
Hybridization
|
the concept of mixing atomic orbitals into new hybrid orbitals (with different energies, shapes, etc., than the component atomic orbitals) suitable for the pairing of electrons to form chemical bonds in valence bond theory
|
|
How to predict hybridization
|
by using the steric number!
|
|
Sigma Bonds
|
Bonds formed by end-to-end overlap of atomic or hybrid orbitals
Electron density is highest in between the nuclei along the bond axis
|
|
Orbitals involved in sigma bonds
|
Atomic and or hybrid orbitals
*hybrid orbitals ONLY form sigma bonds*
|
|
Pi bonds
|
Bond that involves side to side overlap of orbitals
Results in regions of electron density at above and below the bond axis (the imaginary segment that connects the 2 nuclei)
|
|
Orbitals involved in Pi bonds
|
ONLY unhybridized p orbital make these
|
|
How many of each bond type in single bonds?
|
All single bonds are sigma bonds (when using the valence bond theory)
-Sigma bonds are the strongest type of bond
|
|
How many of each bond type in multiple bonds?
|
-Consist of one sigma bond and the rest are pi bonds
-Ex:~ double bond: 1 sigma and 1 pi bond
~triple bond: 1 sigma, 2 pi bonds
|
|
Molecular orbital (MO) theory
|
a method for determining molecular structure in which electrons are not assigned to individual bonds between atoms, but are treated as moving under the influence of the nuclei in the whole molecule
|
|
Tenets of Molecular orbital theory
|
1) Mixing of atomic orbitals: Atomic orbitals are wave functions; they are mathematically combined with each other (add/subtract) and form delocalized molecular orbitals; these orbitals are spread out over the entire molecule
2) Energy considerations: If 2 orbitals are mixed with each …
|
|
Bonding orbitals (MO theory)
|
Wave function: additive combination
Electron density: greater along the bond between nuclei
Energy: lower energy than the atomic orbital
|
|
Antibonding (MO theory)
|
Wave function: subtractive (out of phase) combination
Electron density: greater outside the internuclear region
Energy: Higher energy than the atomic orbital
-antibonding orbitals have a node
-antibonding is indicated by an asterisk
|
|
Parameters that can be determined from MO diagrams
|
Bond order: 1/2 ( # bonding electrons - # antibonding electrons)
Bond types: sigma, pi, or some combination
Magnetic Properties: diamagnetic or paramagnetic
|
|
Atomic mass unit
|
1 amu = (mass of C-12)/12
-unit for atomic mass
|
|
All atomic masses are measured relative to
|
C-12 (carbon 12)
|
|
Why is atomic mass not exactly equal to mass number?
|
A lot of energy is released when nuclei are formed which changes the mass
|
|
% abundance
|
the relative amount of each isotope in a natural sample of a given element
|
|
Atomic mass
|
the weighted average of all isotope masses
-the atomic mass represents the mass (in grams) of 1 mole of an element
|
|
Mole
|
-mole is basically a counting word like "dozen"
-The number of atoms or other particles in a mole is the same for all substances
-there are 6.022 * 10^23 things (usually particles in this case) in 1 mole of anything
|
|
Avogadro's number
|
6.022 * 10^23
|
|
Molar mass (M)
|
- The mass of one mole of a compound (g/mol)
-can also be called molecular weight, formula mass, formula weight
-to calculate it, just add together the individual atomic masses of each element from the chemical formula
|
|
Molecular formula
|
total number of each atoms in a molecule of a compound
|
|
Empirical Formula
|
lowest whole number ratio of atoms in a compound
-For ionic compounds, the empirical formula is the same as the ionic formula
-to find this, just divide the molecular formula by greatest common factor
|
|
Steps to determining empirical formula
|
1) Convert mass of each element to moles
2) Convert to lowest ratio by dividing each molar quantity by the smallest one
3) If necessary, multiply by a small whole number to ensure while number subscripts
|
|
Combustion reactions
|
organic compound + O2 ---> CO2 + H2O + other stuff
|
|
Reactants
|
elements/compounds that are consumed in a reaction
|
|
Products
|
elements/compounds that are formed in a reaction
|
|
Coefficients
|
numbers in front of each symbol that tell you the number of particles/moles of each species that is involved
|
|
Steps for balancing chemical equations
|
1) Arrange reactants and products: reactants on the left, products on the right
2) Add coefficients: set the most complex species to 1
3) Adjust the coefficients: make sure the atoms balance; when possible use whole number coefficients
4) Check the # atoms on left = # atoms on right
5…
|
|
Stoichiometry
|
Calculating the amounts of reactant and/or products involved in a chemical reaction
|
|
Mole Ratios
|
Mole Ratios The coefficients in the balanced chemical equation tell us the relative number of moles of each substance in the reaction
|
|
Determine the limiting reactant/reagent
|
Determine the stoichiometric ratio (R) for each reactant
the reactant with the SMALLEST R is the limiting reactant
|
|
When do you need to determine the limiting reactant?
|
If you're given amount of 2 or more reactants you MUST determine which is the limiting reactant
-if given amount for only one reactant or starting with a product amount, you don't have to determine it
|
|
Theoretical yield
|
maximum amount of product that can be obtained if ALL of the limiting reactant is cosumed
|
|
Actual yield
|
the amount of product that is actually obtained from a reaction
-this happens because 1) experimental losses 2) side reactions 3) reaction isn't completed
|
|
Percent yield
|
always less that or equal to 100
|
|
Solution
|
Homogeneous mixture of two or more substances; single phase; usually involve a liquid
-ex: salt water, most beverages, air, alloys
|
|
Solute
|
minor component of solution; what is dissolved
|
|
Solvent
|
major component of solution; does the dissolving
-liquid (usually water)
|
|
Why is water polar?
|
1) O is more electronegative than H
2) Bent shape: bond dipoles don't cancel out
3) Negative and positive poles
|
|
Solutions of ionic compounds in water
|
-Ions separate in solution
-ions in solution conduct electricity
|
|
Solutions of covalent compounds in water
|
usually there is no bond breaking
|
|
Electrolyte solution
|
a solution that conducts electricity
|
|
Strong electrolytes
|
Soluble ionic compounds or strong acids (HCl, HNO3, H2SO4)
-conduct electricity really well
|
|
Weak electrolytes
|
Compounds partially break down into ions and weakly conduct electricity
-weak acids
|
|
Nonelectrolytes
|
no electrical conductivity
-covalent compounds that are not acids or bases
|
|
Molarity (M)
|
concentration unit
|
|
Dilution
|
-Adding pure solvent to a solution to make a lower concentration solution
-moles of solute stays the same before and after the dilution
-results in a larger volume but a lower molarity
|
|
Precipitation reaction
|
2 solutions are combined and one or more insoluble products forms
|
|
Steps to determine if precipitate will form
|
1) Determine ions in the reactants: separate the reactants into constituent ions
2) Consider all combinations: usually only 2 products are possible
3) Decide whether any combination is insoluble: remember solubility rules
|
|
Molecular (formula) Equation for aqueous ionic reaction
|
the full set of reactants and products written as intact species
|
|
Total Ionic Equation for aqueous ionic reaction
|
separate soluble ionic compounds (aq)
|
|
Net Ionic Equation for aqueous ionic reaction
|
remove "spectator ions" which appear on both sides of the equation
|
|
Acid
|
a compound that releases H+ when dissolved in water
formula is HnX where X is an anion and n is the anion's charge
|
|
Base
|
A compound that releases OH- in water
formula is M(OH)n where M is a cation and n is the cation's charge
|
|
Strong acids/bases
|
Acids/bases that dissociate completely into ions; strong electrolyte
Strong acids: HCl, HBr, HI, HNO3, HClO4, H2SO4
Strong bases: LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2
|
|
Weak acids/bases
|
acids/bases that do not completely dissociate
-most molecules remain intact
Weak acids: HF, H3PO4, CH3COOH
Weak bases: NH3
|
|
Recombination of H+ and OH-
|
-spectator ion and coefficients depend on the identity of the acid and base
|
|
Overall outcome of acid/base reaction
|
Acid + base ---> water + salt
|
|
review these things
|
acid and base nomenclature
the polyatomic ion table
|
|
Oxidation
|
Loss of electrons
|
|
Reduction
|
Gain of electrons
|
|
Mnemonic device for oxidation and reduction
|
LEO says GER
|
|
Oxidation number (ON) rules
|
1) Atom in a neutral element: ON = 0
2) Monatomic ion: ON = charge
3) Sum of oxidation numbers = total charge
4) Metal in ionic compounds: positive ON is = to charge
5) H: ON is +1 when bonded to a nonmetal and -1 when bonded to metals or metalloids (B, Al)
6) F: always -1 in compoun…
|
|
Oxidizing agent
|
the reactant that gets reduced (gains electrons) in a redox reaction
-does the oxidizing
-oxidation number decreases during reaction
|
|
Reducing agent
|
The reactant that gets oxidized (loses electrons) in a redox reaction
-does the reducing
-oxidation number increases during the reaction
|
|
Balancing redox reactions
|
1) Assign oxidation numbers for each atom
2) Determine the number of electrons lost/gained for each species that changes oxidation number
3) Add coefficients to balance electrons lost/gained; get the electrons lost/gained to their least common multiple
4) Balance the rest like normal b…
|
|
Redox reaction
|
a reaction that involves transfer of electrons
|
|
All diatomic molecules have _____ geometry
|
linear
|
|
Bond angles in molecules with lone pairs
|
The lone pair repels the bonding pairs even more than another bond would so the bond angle is a little less
-Bond angles are compressed when lone pairs are present
|
|
Hybrid orbital: sp
|
linear
|
|
Hybrid orbital: sp2
|
trigonal planar
|
|
Hybrid orbital: sp3
|
tetrahedral
|
|
Hybrid orbital: sp3d
|
trigonal bipyramidal
|
|
Hybrid orbital: sp3d2
|
octahedral
|
|
Diamagnetic
|
NO unpaired electrons, weakly repelled by magnetic field
|
|
Paramagnetic
|
1 or more unpaired electrons, attracted to a magnetic field
Can have paired and unpaired electrons
|
|
Aqueous
|
dissolved in water
|
|
When doing net ionic equations with weak acids
|
Don't separate the weak acid reactant into ions
|
Chem 1331: Elements