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| what are the three rules for forming Lewis Dot Structures |
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Definition
find the total number of valence electrons in the entire molecule
use one pair of electrons to form one bond between each atom
use the remaining electrons to fill the duet rule for hydrogen and the octet rule for other atoms |
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Term
| what is one exception to the Lewis Dot structure |
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Definition
| when an atom has more or less valence electrons to fulfill the octet rule |
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Term
| is it true that halogens other than flourine can make more than one bond |
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Definition
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| when determing formal charge, what are two specific things to remember |
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Definition
(1) a bond between two atoms corresponds to one electron for each atom
(2) formal charge is the number of electrons in an isolated atom minus the number of electrons in the molecule |
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Term
| how do you find the index of hydrogen deficiency |
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Definition
if it is an alkane, use: 2n +2
x= the number of hydrogens in the compound
[(2n+2)-x]/2
for any saturated alkane, this equation will equal zero |
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Term
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Definition
| carbon-carbon single bond or methane |
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| carbon-carbon double bond |
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| carbon-carbond triple bond |
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| give some of the IUPAC rules |
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Definition
longest continuous chain is the base name
the end carbon closest to the carbon with a substituent is always the first carbon-if there is a tie, look for the next closest substituent
substituents are given the same number as their carbon
substituents are listed alphabetically
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Term
| what creates molecular bonding |
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Definition
| electrostatic force from the negative charge of electrons and the positive charge of the nuclei |
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Term
| when are electrons at their lowest energy |
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Definition
| when they are closest to a positive charge or farthest from a negative charge |
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Term
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Definition
| bond energy is the average energy to break the bond, therefore: the higher the bond energy the more stable the compound |
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Term
| what is a coordinate covalent bond |
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Definition
| a coordinate covalent bond is when a single nuclei can donate both electrons |
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Term
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Definition
this occurs between two bonding atoms and is a single bond.
it has the lowest energy and is the most stable form of a covalent bond |
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Term
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Definition
| a pie bond occurs when additional bonds form between two sigma bonded atoms |
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Term
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Definition
| above and below the sigma bonds |
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Term
| how do sigma and pie bonds relate in bond strength |
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Definition
| pie bonds are weaker than sigma bonds |
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Term
| how is bond strength related to bond length |
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Definition
| they are inversely proportional; the smaller the bond length, the greater the bond strength |
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Term
| which is more reactive, pie or sigma bonds |
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Definition
| pie bonds, because they are further from the nuclei and have higher energy states, therefore, more unstable and more reactive |
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Term
| what are the several types of hybrid orbitals |
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Definition
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Term
| how can you determine the type of hybrid orbital present in a compound |
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Definition
count the number of sigma bonds and lone pairs of electrons and match this with the superscript
remember that s has one orbital to fill and p has three orbitals to fill |
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Term
| what is the character of an sp hybrid orbital |
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Definition
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Term
| how can you determine the stability of a molecule using characters of their orbital |
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Definition
| the more s percentage that is in it's character means the shorter the bond lengths and the more stable the molecule is |
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Term
| what can distort predicted bond angles |
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Definition
| lone pairs, pie bonds & ring strain |
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Term
| what are four rules for resonance structures |
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Definition
atoms must not be moved- move electrons not atoms
number of lone pairs must stay constant
all resonance atoms must lie in the same plane
onnly applicable for pie bonds (just for MCAT purposes)
only proper Lewis Dot Structures |
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Term
| what are two conditions to look for in resonance structures |
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Definition
a species must contain an atom with a p orbital or an unshared pair of electrons
that atom must be single bonded to another atom with a double bond or triple bond (in other words- a conjugated system) |
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Term
| with ring structures, resonance is only applicable if |
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Definition
| Huckel's rule is fulfilled (aromatic test: 4n+ 2) and so are the four basic steps |
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Term
| when a molecule has a dipole movement it is refered to as |
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Definition
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Term
| when a molecule does not have a dipole movement it is refered to as |
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Definition
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Term
| what is an induced dipole and how does it compare to permant dipoles |
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Definition
an induced dipole occurs when a polar molecule or ion creates an electric field, which pushes the electrons and nuclei in opposite directions
these are generally weaker than permant dipoles |
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Term
| what are instantaneous dipoles |
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Definition
| can existed nonpolar molecules because at any moment the electrons in orbital may not be exactly between two bonds and thus induce an instantaneous dipole-that can induce additional dipoles in neighboring molecules |
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Term
| give an example of intermolecular attractions |
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Definition
| hydrogen bonding- a positively charged part of a molecule is attracted to a negatively charged part the same molecule and they bind- typically very weak bonds |
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Term
| what is a London Dispersion Force |
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Definition
| the weakest dipole-dipole force that is between to instantaneous dipoles |
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| intramolecular and intermolecular forces are |
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Definition
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| very low energy and is a stable bond |
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| what is the easiest way to distinguish between conformational isomers |
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Definition
| use Newman projections: eclipsed, fully eclipsed, gauche, anti- staggered |
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Term
| what is a structural isomer |
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Definition
| a structural isomer has the same molecular formula but different connectivity |
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Term
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Definition
| stereoisomers have the same molecular formula and have the same connectivity as each other |
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Term
| how can you determine if a molecule is chiral |
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Definition
| a chiral molecule has four different substituents |
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Term
| in absolute configuration, what directions do R and S go |
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Definition
| R is clockwise, and S is counter-clockwise |
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Term
| in absolute configuration, what is given highest priority and lowest priority |
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Definition
| it is based on atomic weight- the higher the weight, the greater the priority |
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Term
| what is relative configuration |
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Definition
| when two molecules resemble each other except for one substituent |
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Term
| what is observed rotation |
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Definition
| the direction and degree to which a compound rotates plane-polarized light |
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Term
| what does a polarimeter do |
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Definition
| screens out photons with all but one orientation of electric field |
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Term
| compounds that are optically inactive are |
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Definition
compounds that do not orient themselves in any single orientation, leaving the net force equal to zero
also called a racemic mixture |
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Term
| what are the symbols for optically active |
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Definition
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Term
| stereoisomers must contain at least one what |
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Definition
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Term
| enatiomers have the same chemical and physical properties except for |
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Definition
| reactions with chemicals and direction they polarize light |
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Term
| give three examples of diastereomers |
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Definition
| geometric isomers, cis and trans isomers |
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Term
| what predictions can be made concerning the melting and boiling points of geometric isomers |
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Definition
| due to their molecular dipole movement, cis isomers have a higher probability of intermolecular attractions, thus the boiling point for cis isomers is higher than trans. however, due to their lack of symmetry, cis isomers have a lower melting point because they do not form crystals |
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Term
| steric hindrance in cis molecules produces |
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Definition
| higher energy levels resulting in high heats of combustion |
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Term
| what is the maximum number of optically active isomers a single compound can have |
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Definition
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Term
| meso compounds are achirl, wh? and what does this mean |
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Definition
| meso compounds are achirl because they have two chiral centers that offset each other making them optically inactive |
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