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When two hydrogen atoms come close together, __ begin to develop between them. What happens with the nuclei and electrons?
- electrostatic interactions
- the two positively charged nuclei repel each other, and the two negatively charged electrons repel each other, but each nucleus attracts both electrons
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If the attractive forces are __ than the __ forces, a covalent bond is formed, with the two atoms __ and the two shared eletrons __.
- stronger
- repulsive
- held together
- occupying the region between the nuclei
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The __ of hte various attractive and repulsive forces between __ and __ in a __ depend on how close the atoms are.
- magnitudes
- nuclei
- electrons
- covalent bond
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If the atoms are too far apart, what happens? too close?
Thus, there is an optimum distance between nuclei called the __ where net attractive forces are maximized and the H-H molecule is most stable.
- far: attractive forces small and no bond exists
- repulsive interaction between nuclei becomes so strong it pushes atoms apart
- bond length
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Every __ has its own characteristic length that leads to __ and that is roughly predictable from a knowledge of __.
- covalent bond
- maximum stability
- atomic radii
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Bond dissociation energies are always ___. Why?
- positive
- energy must be supplied to break a bond
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The amount of energy released on forming a bond always has a __ value.
negative
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Why are ionic compounds high-melting solids?
Fpr sodium chloride to melt or boil so that the ions break free of one another, every ionic attraction int the entire crystal--the __-- must be overcome, a process that requires a large amount of energy.
- ionic bonds
- lattice energy
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What symbol represents the resultant partial charges on the atoms?
lowercase Greek letter delta
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maps that use olor to portray the calculated electron distribution in an isolated, gas-phase molecule.
electrostatic portential maps
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Where are the least EN items found? highest?
- lowest from top to bottom
- highest from left to right
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The pairs of electrons that are nonbonding
lone pairs
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shared electrons
bonding pair
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In speaking of moolecules with multiple bonds, we often use the term __ to refer to the number of electron pairs shared between atoms.
bond order
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bonds that form when one atom donates a lone pair to another atom that has a vacant valence orbital
coordinate covalent bonds
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When the octet rule fails, it often does so for elements toward the __ of the periodic table that are in the __ row and lower.
Why?
- right side
- third
- They are larger, can accomodate more than four atoms close around them, and therefore form more than four bonds
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Resonance hybrid
the actual electronic structure is an average of the different possibilities
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How to calculate formal charge?
number of valence in free atom- (1/2) Number of bonding electrons- number of nonbonding electrons
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The number of charge clouds is the __.
total bumber of bonds and lone pairs
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Both the electron dot model and VSEPR model do not say what?
say anything about the electronic nature of covalent bonds
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To describe bonding, a quantum mechanical model called __ has been developed. It provides an easily visualized orbital picture of how electron pairs are shared in a covalent bod.
valence bond theory
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In the valence bond model, the two overlapping lobes must be of the __, and teh strength of the covalent bond that forms depends on the amount of __ overlap: the __ the overlap, the __ the bond.
This, in turn, means that bonds formed by overlap of other than s orbitals have a __ to them.
- phase
- orbital overlap
- greater
- stronger
- directionality
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Such bonds that result from head-on orbital overlap are called __.
sigma bonds
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What are the principles of valence bond theory?
- covalent bonds are formed by overlap of atomic orbitals, each of which contains one elctron of opposite spin. The two overlapping lones must be of the same phase.
- Each of the bonded atoms maintains its own atomic orbitals, but the electron pair in the overlapping orbitals is shared by both atoms.
- The greater the amount of orbital overlap, the stronger hte bond. This leads to a directional character for the bond when other than s orbitals are involved.
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How can carbon form four bonds if two of its valence electrons are already paired and only two unpaired electrons remain for sharing?
- electron must be promoted from the lower energy 2s orbital to the vacant, higher-energy 2pz orbital, giving an excited state configuration [He] 2s1 2px1 2py1 2pz1 that has foour unpaired electrons and can thus form four bonds
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Linus Pauling introduced the idea of __. Pauling showed how the __ for s and p atomic orbitals derived from the __ can be mathematically combiined to form a new set of equivalent wave unctions called __.
Ex: When one s orbital combines with three p orbitals, as occurs in an __, four equivalent hybrid orbitals, called __, result.
- hybrid orbitas
- quantum mechanical wave functions
- Schrodinger wave equation
- hybrid atomic orbitals
- excited-state carbon atom
- sp3 orbitals
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Each sp3 hybrid ornital has two lobes, of __,one of which is larger than the other.
different phase
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The shared electrons in a covalent bond made with a spatially directed hybrid orbital spend most of hteir time in the region between the __.
two bonded nuclei
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Atoms with three charge clouds undergo hybridization by combination of one atomic s orbital with two p ornitals, resulting in three __.
sp2 hybrid orbitals
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What happens to the unhybridized p orbitals on the carbons as the two sp2 hybridized carbon atoms approach each other with sp2 orbitals aligned head-on for sigma bonding?
the unbybridized p orbitals on the carbons approach oeach other in a parallel, sideways manner rather than head on, occupying regions above and below a line connecting hte nuclei rather than directly, called a pi bond
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The __ bond has __ regions of orbital overlap, one above and one below a line drawn between the nuclei, the __. Both regiosn are part of the same bond, and the two shared electrons are spread over both regions. As always, the p lobes must be of the same __ for overlap, leading to __. The net reaction of both sigma and pi bonds is __.
- pi
- two
- internuclear axis
- phase
- the sharing of four electrons and the formation of a carbon-carbon double bond
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A given shell has a total onf only __ s and p orbitals.
four
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2 charge clouds
Arrangement and hybridization?
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3 charge clouds
Arrangement and hybridization?
trigonal planar sp2
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4 charge clouds
Arrangement and hybridization?
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Atomic orbitals on the same atom can do what?
combine to form hybrids
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Atomic orbitals on different atoms can overlap to do what?
form covalent bonds, but the orbitals and electrons in htem remain localized on specific atoms
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atomic orbital
a wave function whose square gives hte probability of finding an electron within a given region of space in an aotom
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Molecular orbital theory considers what?
the molecule as a whole rather than the individual atoms
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molecular orbital
a wave function whose square gives the probability of finding an electron within a given region of space in a molecule
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Molecular orbital theory has two ways for interaction...__ and __
additive nad subtractive way
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The additive combo, denoted sigma, is __ in energy than the two isolated 1s orbitals and is called a __ because any electrons it contains spends most of their tiime in the region between the two nuclei, bonding the atoms together.
- lower
- bonding molecular orbital
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In the molecular orbitals, a net gain results in __, while a neutral (no net bondign energy) results in __.
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bond orders
the number of electron pairs shared between atoms
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how to determine bond order?
(# of bonding electrons- # of antibonding electrons)/2
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A molecular orbital describes what?
a region of space in a molecule where electrons are most likely to be found, and it has a specific size, shape, and energy level
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Molecular orbitals are formed how?
by combining atomic orbitals on different atoms
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Molecular orbitals are __ in energy than the starting atomic orbitals are __, and MOs that are __ in energy than the starting atomic orbitals are __.
- lower
- bonding
- higher
- antibonding
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Electrons occupy molecular orbitals beginning with the __. A maximum of __ electrons can occupy each orbital, and their spins are paired.
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Substances with unpaired electrons are attracted by magnetic fields and are thus said to be __.
paramagnetic
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The more unpaired electrons a substance has, the stronger the __ attraction.
paramagnetic
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Substances whose electrosn are all spin-paired, by contrast, are weakly repelled by magnetic fields and are said to be __.
diamagnetic
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__ is better because of its simplicity and ease of visualization, but __ is better because of its accuracy.
- valence bond theory
- MO theory
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What are the two problems with valence bond theory?
- for olecules like O2, it makes an incorrect prediction about electronic structure
- for molecules like O3, no single structure is adequate and resonance must occur
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