Kaplan General Chemistry Unknown Concepts Flashcards
(63 cards)
What are the quantum numbers?
n: energy of shell (rows of the periodic table)
- max number of electrons in a shell: 2n^2
- n^2 orbitals
l: subshell (s,p,d,l)
[0 - (n-1)]
- 4l+2
ml: specifies orbital within a subshell
(-l to l); 2l + 1 values
ms: spin (+/- 1/2)
d orbitals always fill to 5 or 10 over the 4s
What is paramagnetic vs. diamagnetic?
paramagnetic: unpaired electrons; attract material to magnet from parallel spins in electrons
dimagnetic: all paired; repelled by magnets
What is Planck’s relation for energy in terms of frequency and wavelength?
E=hf
E=hc/lambda
What are periods and groups?
periods = rows
groups = columns, same valence shell electron configuration
What is effective nuclear charge Zeff?
net positive charge experienced by electrons in the valence shell
- increases from left to right
Zeff = protons - nonvalence electrons
What are the exceptions to the octet rule?
incomplete octet: H (2), He (2), Li (2), Be (4), B (6)
expanded octet: all elements in period 3 or greater
What are coordinate covalent bonds?
when single atom provides both bonding electrons while the other atom does not contribute any
- Lewis acid base chemistry
What is formal charge?
when atom is surrounded by more or fewer valence electrons than it has in neutral state
= V - Nnonbonding - 1/2Nbonding
= valence electrons - dots - sticks
What is VSPER theory?
3D molecular geometry of covalently bonded molecules; electrons will arrange themselves as far away as possible
nonbonding: more repulsion because they are closer to the nucleus
ELECTRONIC CONFIGS
linear: 2 atoms; 180
trigonal planar: 3 atoms; 120
tetrahedral: 4 atoms; 109.5
trigonal bipyrimidal: 5 atoms; 90, 120, 180
octahedral: 6 atoms; 90, 180
What are the electronic and molecular shapes of CH4, NH3, and H2O?
all three have tetrahedral electronic geometry
CH4: tetrahedral
NH3: trigonal pyramidal
H2O: bent
What are sigma and pi bonds?
sigma: head to head overlap
pi: overlap of two parallel electron clouds
Give the order of the strength of intermolecular forces.
1) ionic bonds
2) covalent bonds
3) hydrogen bonds: H bonded to FON
4) dipole-dipole: oppositely charged ends of polar molecules; negligible in gas phase
- dipole moment = p = qd
5) LDF: present in all atoms and molecules
What are equivalents and normality?
Equivalents (Eq)
- number of moles of reactive units (protons, electrons, or ions) in a substance that reacts with or supplies one mole of H⁺ or OH⁻ in an acid-base reaction, or one mole of electrons in a redox reaction.
- moles substance * n factor (number of reactive units)
- mass of compound * n / molar mass
Normality (N)
- concentration unit expressed as the number of equivalents of solute per liter of solution.
- molarity * n
What is the formula for percent composition?
(mass of element in formula / molar mass) * 100
What is the difference between empirical and molecular formula?
empirical: simplest whole number ratio of elements in a compound
molecular: exact number of atoms in a compound
- normally the same or a multiple of the empirical
How do you determine the limiting reactant?
1) make sure equation is balanced
2) determine molar amounts of each reactant using the coefficients in the equation
3) determine amount of product
How do you name polyatomic anions?
hypochlorite O, chlorite O2, chlorate O3, perchlorate O4
What is the Arrhenius equation?
represents collision theory; rxn rate is proportional to the number of effective collisions (proper orientation and kinetic energy)
rate = Z x f
- Z: total number of collisions
- f: fraction of collisions that are effective
k = Ae^(-Ea/RT)
- low activation energy + high temperature increases k
What is the free energy change of a reaction?
deltaG products - deltaG reactants
- negative means exergonic, energy given off
- positive, endergonic, energy absorbed
How do you affect reaction rate ?
1) increasing the concentration of reactant will increase the reaction rate ~ more effective collisions
2) increasing temperature increases rate ~ more kinetic energy
3) changing the medium can increase or decrease rate, depending on how the reactants interact with it
4) adding a catalyst lowers activation energy
Describe rate laws.
rate = k[A]^x [B]^y
- usually do not match stoich coefficients unless single step mechanism (no int), have to be determined experimentally
- 0 order reactions have constant rate
Describe the graphs of concentration vs. time curve for each order reaction.
0: straight line, slope is -k
- temp and catalyst are the only thing that can change
1: nonlinear; slope of ln [A] is linear and = -k
2: nonlinear; slope of 1/[A] is linear and = k
what is the difference between Q and Keq?
Q: value that relates reactant to product concentrations at any given time during a rxn
Keq: ratio of products to reactants at equilibrium, each being raised to stoich coefficient
- constant with constant temperature
if Q<K, delta G <0, then reaction proceeds forward
if Q = K, delta G = 0, dynamic equilibrium
if Q > K, delta G >0, reaction proceeds in reverse direction
What is Le Chatlier’s principle?
1) increasing concentration of reactants or decreasing products will shift the reaction to the right
2) increasing the pressure on gaseous system (decreasing volume) will shift the rxn towards the side with fewer moles of gas
3) increasing the temperature of an endothermic reaction or decreasing the temperature of an exothermic reaction will shift the reaction to the right
