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Higher in energy than bonding orbitals; contains electrons "out of phase" that are said to be "repulsive".
Lower in energy than anti-bonding orbitals; contain electrons that are "in phase" that are said to be "attractive".
Covalent compounds that dissociate 100% in water (strong acids and strong bases) and ionic compounds are always good electrolytes.
The condosity of a solution is defined as the molar concentration of sodium chloride that has the same specific electrical conductance as the solution.
(ex. 3M LiCl has a condosity of less than 3M because Na has more metallic character than Li so a lower concentration of Na Cl would be sufficient to conduct electricity just as well)
The energy stored in a bond. This is the amoung of energy that will be required to break the bond. Therefore, stable compounds have the highest bond energies, and unstable compounds have low bond energies.
According to the MCAT this is also known as "bond dissociation energy".
Heat of Combustion
The higher the energy of the molecule (i.e. less stable) the higher the heat of combustion.
Empirical vs Molecular formulas
The empirical formula is the simplest formula for a compound. A molecular formula is the same as or a multiple of the empirical formula, and is based on the actual number of atoms of each type in the compound. For example, if the empirical formula of a compound is C3H8 , its molecular formula may be C3H8 , C6H16 , etc.
The percent mass of one element in the formula/total mass of all elements in the formula.
Deriving a formula from percent mass
- 1) Change the percent for each species into grams.
- 2) Convert the grams of each species into moles by dividing by molar mass.
- 3) Look at the element with the lowest number of moles. Calculate approximately how many times it will divide into each of the other molar amounts for each of the other elements -- this number is the subscript for each element in the empirical formula. If the subscripts are not at there lowest common denominator, reduce to get the empirical formula.
AN EMPIRICAL FORMULA IS ALL YOU CAN GET FROM PERCENT MASS ALONE. TO GET THE MOLECULAR FORMULA, YOU MUST BE GIVEN THE MW OF THE UNKOWN COMPOUND. Then simply divide that MW by the MW of the empirical formula. You should get a whole number. Multiply each subscript by that number to get the molecular formula.
A + B
Single Displacement Reaction
AB + C
AC + B
Double Displacement Reaction (Metathesis Reaction)
AB + CD
AC + BD
How to name general Ionic compounds
Name the cation first, then the anion (e.g., CaSo₄ is Calcium Sulfate)
How to name Transition Metals
When written in words, compounds including transition elements must have a roman numeral showing the oxidation state of the metal (i.e., Iron(II)Sulfate vs. Iron(III)sulfate).
How to name Monatomic ions
Named by replacing the last syllable with "ide" (i.e., Sulfide, Hydride, Chloride, etc.)
How to name Acids
"ate" becomes "ic" (Sulfuric/Nitric acid)"ite" becomes "ous" (Nitrous acid)"ide" becomes "hydro/ic" (hydroiodic/hydroflouric acid)
Steps in balancing reactions
- 1) Balance Carbons
- 2) Balance Hydrogens
- 3) Balance oxygens
- 4) Balance others
- 5) Finally, multiply all species by the number in the denominator of any fraction to remove the fractions
How to find limiting reagent
- 1) Convert to moles
- 2) Balance the equations
- 3) compare the number of moles you have to the number of moles required to run one cycle of the reaction.
The reactant you run out of first is the limiting reagent. This may not
always be the reactant you have the least of (grams or moles).
Trick for finding which compound requires more oxygen to combust
Add 1 point for each carbon there is and subtract 1/2 for each oxygen there is in the compound...the compound with the highest point value requires the greatest number of oxygens
Theoretical Yield: products formed when all the limiting reagent is used.
Actual Yield: product obtained from reaction - always less then theoretical yield.
Percent Yield: actual/theoretical X 100%
- Keq = [products]x / [reactants]y
- Keq is written with every term raised to an exponent equal to its coefficient in the balanced equation (remember, however, that you do NOT do this when writing rate laws). Pure liquids (l) and pure solids (s) are never included!
The Reaction Quotient (Q)
The equilibrium constant can ONLY by calculated at equilibrium. IF you make the exact same calculation using concentration values taken at any point other than equilibrium the result is called the REACTION QUOTIENT, Q.
- If Q > K, run will proceed to the left
- If Q < K, run will proceed to the right.
How does increasing temperature in an exothermic reaction change Keq?
Increases it which shifts the equilibrium to the left making more reactants.
(Le Chatelier) Add Reactants
(Le Chatelier) Add Products
(Le Chatelier) Increase Pressure
Shift to side with the less gas molecules
(Le Chatelier) Increase temperature
Shift toward side that heat species is not on.
Polar molecule characteristics
Highest electronegativity and smallest radius.
One atom provides both electrons to the bond and the other has an empty valence shell.
Almost always includes a transition metal.
NH3 is very very commonly used.
Phase state of ionic compounds
Solids at room temp.
1 cm3 is equivalent to...
Accompanies most all radioactive decay
Gamma ray emission.
Ration of products over reactants raised to their coefficients in the balanced equation.
Strong acids dissociate 100% and therefore are all product over almost no reactant.