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chemical bonding II:
molecular shapes, valence bond theory, and molecular orbital theory
74
Chemistry
Undergraduate 1
12/01/2008

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Term
valence shell electron pair repulsion (VSEPR)theory is based on what?
Definition
the simple idea that electron groups, which we define as lone pairs, single bonds, multiple bonds, and even single electrons, repel one another through coulombic forces. Repulsions between electron groups determine molecuular geometry.
Term
which occupies more space, a bonding pair or a nonbonding pair of electrons?
Definition
a nonbonding pair
Term
tetrahedral geometry is like how many balloons tied together?
Definition
four balloons
Term
five electron groups around a central atom assume a ______ bipyramidal geometry
Definition
trigonal
Term
six electron groups around a central atom assume a ________ geometry, like that of _____ balloons together
Definition
octahedral geometry; six balloons
Term
in a five electron group with lone pairs, is the axial or the equatorial position more favorable for lone pair electrons? why?
Definition
the equatorial position; because it has only 2 90 degree interactions with bonding pairs.
Term
what 5 things count as a single electron group?
Definition
a lone pair, a single bond, a double bond, a triple bond, or a single electron
Term
all ______ ______ on the central atom determine the shape of a molecule according to the VSEPR theory
Definition
electron groups
Term
what degree do three bonding pairs have between them?
Definition
120 degree
Term
how many degrees between hydrogen would CH4 assume, since it has no lone pairs?
Definition
109.5
Term
____ lone pair(s) is = to 107 degrees in NH3
Definition
one lone pair
Term
109.5 degree is ideal for how many lone pairs in tetrahedral geometry? (water, for instance)
Definition
two lone pairs
Term
what would the geometry look like of an element with five electron GROUPS? what are the angles?
Definition
a trigonal bypyramid one on top, one on bottom, three around axis; 90 degrees from the top or bottom to the axial groups, and 120 degrees for in between the axial groups
Term
what does tetrahedral geometry look like? how many electron groups is this?
Definition
a molecule with four or more electron groups would have tetrahedral geometry; there is one group at the top of the central atom, and three groups that are at 109.5 degree angles around the axis in the lower portion
Term
what kind of geometry would six electron groups make? what would it look like? what is the degree in between all of the balloons
Definition
octahedral geometry. it would have one group on top, one on bottom, and four around the central axis; 90 degrees
Term
VSEPR stands for
Definition
valence shell electron pair repulsion
Term
two lone pairs in H20 would be what degree for the ACTUAL molecular geometry?
Definition
104.5 degree
Term
in SF4 it creates what molecular geometry? (because of the equatorial lone pair, it has 5 electron groups)
Definition
seesaw
Term
in BrF3, two of the five electron groups around the central atom are lone pairs. what positions would the lone pairs occupy and why? what is the electron geometry of this structure and what is the molecular geometry?
Definition
they are in the equatorial positions. this minimizes 90 degree interactions. the electron geometry is trigonal bipyramidal and the molecular geometry is T-shaped
Term
in BrF5 there are six electron groups because of a lone pair. what is the electron geometry and the molecular geometry?
Definition
the electron geometry is octahedral, and the molecular geometry is square pyramidal
Term
when two of the six electron groups around the central atom are lone pairs, what positions do the lone pairs occupy? what is the electron & molecular geometry?
Definition
the occupy the axial positions. electron geometry is octahedral and molecular geometry is square planar
Term
three electron groups around a central atom is what electron & molecular geometries?
Definition
trigonal planar, trigonal planar
Term
is a molecule polar or nonpolar if 2 polar bonds are "bent"?
Definition
polar- you iextend a vector between them
Term
is a molecule nonpolar or polar if it has three identical polar bonds at 120 degrees from each other?
Definition
non nonpolar
Term
if the dipole moments of four identical polar bonds in a tetrahedral arrangement cancel, is it polar or nonpolar?
Definition
nonpolar
Term
the dipole moments of three polar bonds in a trigonal pyramidal arrangement (109.5 degrees from eachother) will cancel or not cancel? therefore it is, polar or nonpolar?
Definition
they will not cancel and result in a dipole moment vector. it is polar.
Term
dipole moment
Definition
a measure of the separation of positive and negative charge in a molecule
Term
electronegativity
Definition
the ability of an atom to attract electrons to itself in a COVALENT BOND
Term
enthalpy
Definition
the sum of the internal energy of a system and the product of its pressure and volume; the energy associated with the breaking and forming of bonds in a chemical reaction
Term
arrange the electron group repulsions from order of greatest to smallest lonepair/bonding pair, bonding pair/bonding pair, lone pair/lone pair
Definition
lone pair/lone pair > lone pair/bonding pair > bonding pair/bonding pair
Term
what are the 3 steps in determining if a molecule is polar?
Definition
1) Draw a Lewis structure for the molecule and determine the molecular geometry
2) determine whether the molecule contains polar bonds
3) determine whether the polar bonds add together to form a net dipole moment
Term
why do oil and water not mix?
Definition
water is polar, so its molecules interact strongly with one another and clump together
Term
is OH polar or nonpolar? will it attract water?
Definition
OH is polar, and yes.
Term
valence bond theory
Definition
an advanced model of chemical bonding in which electrons reside in quantum-mechanical orbitals localized on individual atoms that are a hybridized blend of standard atomic orbitals; chemical bonds result from an overlap of these orbitals
Term
the interaction energy is usually ________ (or stablizing) when the interacting atomic orbitals contain a total of two electrons that can spin-pair. what theory does this come from?
Definition
negative energy; valence bond theory
Term
a chemical bond result from the overlap of what? what kind of pairing do they do? what is the less common kind of overlap?
Definition
a chemical bond result from the overlap of two HALF FILLED ORBITALS with SPIN PAIRING of the two valence electrons (or less commonly the overlap of a completely filled orbital with an empty orbital)
Term
what is a covalent chemical bond according to Lewis theory?
Definition
the sharing of electrons (represented by dots)
Term
what is a covalent chemical bond according to valence bond theory?
Definition
the overlap of half-filled atomic orbitals
Term
what does hybridization in the valence bond theory recognize?
Definition
that the orbitals in a molecule are not necessarily the same as the orbitals in an atom
Term
hybrid orbitals
Definition
orbitals formed from the combination of standard atomic orbitals that correspond more closely to the actual distribution of electrons in a chemically bonded atom
Term
hybridization
Definition
a mathematical procedure in which standard atomic orbitals are combined to form new, hybrid orbitals
Term
hybrid orbitals (minimize/maximize) the orbital overlap in a bond. this (minimizes/maximizes) the energy of the molecule.
Definition
maximize; minimizes
Term
a greater overlap in a molecule means (stronger/weaker) bonds
Definition
stronger
Term
metals
Definition
held together by metallic bonding. Metals tend to lose electrons to form cations. These lost electrons form what is known as a "sea of electrons" to which the positively charged cations are attracted.
Term
molecular solids
Definition
are substances made up of covalent molecules that are cold enough to be frozen. Ice is an example of a molecular solid.
Term
covalent (network) solids
Definition
substances made up of atoms held together by interconnecting covalent bonds. Quartz is an example.
Term
what is the electronic geometry of H20?
Definition
tetrahedral
Term
the electronic geometry of a molecule with 5 electron groups is called
Definition
trigonal bypyramidal
Term
pi bond
Definition
when p orbitals overlap side by side
Term
sigma bond
Definition
when orbitals overlap end to end
Term
a single bond is a ______ bond
Definition
sigma
Term
a double bond is a _____ and a ___ bond
Definition
sigma and pi
Term
triple bond consists of a ____ bond and two ____ bonds
Definition
sigma pi
Term
isomer
Definition
compound with the same molecular formula but different structures or different spatial arrangement of atoms
Term
sp hybridization is what electron geometry?
Definition
linear
Term
trigonal planar (3 groups) is what hybridization?
Definition
sp2
Term
sp3 is linear, trigonal planar or tetrahedral?
Definition
tetrahedral
Term
sp3d is what shape?
Definition
trigonal bypyramidal
Term
an octahedral electron geometry is what hybridization?
Definition
sp3d2
Term
molecular orbital theory
Definition
an advanced model of chemical bonding in which the electrons reside in molecular orbitals delocalized over the entire molecule. In the simplest version, the molecular orbitals are simply linear combinations of atomic orbitals.
Term
bonding orbital
Definition
a molecular orbital that is lower in energy than any of the atomic orbitals from which it was formed
Term
antibonding orbital
Definition
a molecular orbital that is higher in energy than any of the atomic orbitals from which it was formed
Term
does the bonding molecular orbital arise from constructive or destructive interference?
Definition
constructive
Term
destructive interference between the atomic orbitals results in what molecular orbital?
Definition
antibonding molecular orbital
Term
bonding orbitals have increased electronic density in the internuclear region, with a greater/lesser energy than nonbonded atoms
Definition
lesser
Term
is the energy in antibonding orbitals higher or lower than in the orbitals of nonbonded atoms? why?
Definition
the energy is higher, because the electron density in the internuclear region is lower
Term
bond order=
Definition
(# of electrons in bonding MOs)-(#of electrons in antibonding MOs),
divided by 2
Term
a + bonding order implies that the molecule is stable/unstable
Definition
stable
Term
the higher the bond order, the stronger/weaker the bond
Definition
stronger
Term
paramagnetic
Definition
attracted to an external magnetic field because of unpaired electrons.
Term
the more electronegative an element, the lower/higher the energy in the atomic orbitals
Definition
lower
Term
nonbonding orbitals
Definition
an orbitals whose electrons remain localized on an atom
Term
if the bond order is 0, does the molecule exist?
Definition
no
Term
when finding the hybridization, a double bond counts for how many charge clouds?
Definition
1
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