Chem: Chapter 9
bonding pair; electron domain; nonbonding pair
A ________________ __________ of electrons thus defines a region in which the electrons are most likely to be found. We will refer to such a region as an ______________ _____________. Likewise, a _________________ ___________ (or lone pair) of electrons, defines an electron domain that is located principally on one atom.
single; double; triple; possible
A bond order of 1 represents a _____________ bond, a bond order of 2 represents a _____________ bond, and a bond order of 3 represents a _______________ bond. Because MO theory also treats molecules containing an odd number of electrons, bond orders of 1/2,3/2, or 5/2 are _________________.
nodal plane
A flat (planar) region of space with zero electron density.
Electronegativity
A measure of the ability of an atom in a chemical compound to attract electrons
more; less
A paramagnetic substance appears to weigh ___________ in the magnetic field; a diamagnetic substance appears to weigh ____________.
sp
According to the valence-bond model, a linear arrangement of electron domains implies ________ hybridization.
nuclear charge; valence
All of these elements have an identical core of electrons, corresponding to the noble-gas configuration of [Ne]. Therefore, the main determining factor of the effective nuclear charge is actual _________________ ______________ of the nucleus (Z). These two values are directly proportional. The value of Z is determined by the number of protons in the nucleus, which corresponds to the atomic number. Keep in mind that the question is asking for the Zeff to be ranked for the electrons in the n=3 electron shell for the elements, not necessarily the Zeff for the _______________ shell.
linear; bent; triangle; triganol planar; triganol pyramidal; T-shaped
An AB2 molecule must be either ______________ (bondangle=180°) or ___________ (bondangle≠180°). For AB3 molecules, the two most common shapes place the B atoms at the corners of an equilateral ________________. If the A atom lies in the same plane as the B atoms, the shape is called ________________ _____________. If the A atom lies above the plane of the B atoms, the shape is called _________________ _________________. (a pyramid with an equilateral triangle as its base). Some AB3 molecules, such as ClF3, are __________________, a relatively unusual shape. The atoms lie in one plane with two B—A—B angles of about 90°, and a third angle close to 180°.
repelled; stable
An electron in an antibonding MO is ________________ from the bonding region and is therefore less _____________ (it has higher energy) than it is in the 1s atomic orbital of a hydrogen atom.
carbocation
An organic ion in which a carbon atom has a positive charge
increases; decrease; increase
As bond order _________________, bond distances __________________ and bond enthalpies ___________________.
decreases; increases; repulsion; balanced
As the distance between the atoms decreases, the overlap between their 1s orbitals increases. Because of the resulting increase in electron density between the nuclei, the potential energy of the system __________________. That is, the strength of the bond _______________, as shown by the decrease in the potential energy of the two-atom system. However, Figure 9.13 also shows that the energy increases sharply when the distance between the two hydrogen nuclei is less than 0.74 Å. The increase in potential energy of the system, which becomes significant at short internuclear distances, is due mainly to the electrostatic ________________ between the nuclei. The internuclear distance at the minimum of the potential-energy curve corresponds to the bond length of the molecule. The potential energy at this minimum corresponds to the bond strength. Thus, the observed bond length is the distance at which the attractive forces between unlike charges (electrons and nuclei) are _________________ by the repulsive forces between like charges (electron-electron and nucleus-nucleus).
decreases
As the distance between the atoms increases, the overlap between their bonding orbitals _______________.
0; bond; not
Because He2 has two bonding electrons and two antibonding electrons, it has a bond order of _______. A bond order of 0 means that no ____________ exists. Molecular orbital theory correctly predicts that hydrogen forms diatomic molecules but helium does __________.
stable; covalent
Because an electron in this MO is attracted to both nuclei, the electron is more ____________ (it has lower energy) than it is in the 1s atomic orbital of an isolated hydrogen atom. Further, because this bonding MO concentrates electron density between the nuclei, it holds the atoms together in a ________________ bond.
valence; not
Because both the σ1s and σ∗1s MOs of Li2 are completely filled, the 1s orbitals contribute almost nothing to the bonding. The single bond in Li2 is due essentially to the interaction of the ______________ 2s orbitals on the Li atoms. This example illustrates the general rule that core electrons usually do __________ contribute significantly to bonding in molecules. The rule is equivalent to using only the valence electrons when drawing Lewis structures. Thus, we need not consider further the 1s orbitals while discussing the other period 2 diatomic molecules.
not
Because the electrons in σ bonds are localized in the region between two bonded atoms, they do __________ make a significant contribution to the bonding between any other two atoms.
180; 120; 109.5; 90, 120; 90, 90
Bond Angles AB2 Linear: AB3 Triganol Planar: AB4 Tetrahedral: AB5 Triganol Bipyramidal (2): AB6 Octahedral (2):
vector; magnitude; direction; zero; nonpolar
Bond dipoles and dipole moments are _____________ quantities; that is, they have both a ________________ and a ________________. The dipole moment of a polyatomic molecule is the vector sum of its bond dipoles. Both the magnitudes and the directions of the bond dipoles must be considered when summing vectors. The two bond dipoles in CO2, although equal in magnitude, are opposite in direction. Adding them is the same as adding two numbers that are equal in magnitude but opposite in sign, such as 100+(−100). The bond dipoles, like the numbers, "cancel" each other. Therefore, the dipole moment of CO2 is ___________, even though the individual bonds are polar. The geometry of the molecule dictates that the overall dipole moment be zero, making CO2 a _________________ molecule.
overlap; half
Covalent bonds are formed through the ______________ of ___________-filled valence orbitals. Because of the overlapping, it is most probable that electrons are located within the region of the bond.
single; central
Each nonbonding pair, single bond, or multiple bond produces a _____________ electron domain around the ________________ atom in a molecule.
greater
Electron domains for multiple bonds exert a _______________ repulsive force on adjacent electron domains than do electron domains for single bonds.
bonding; stable
Electrons occupying a bonding molecular orbital are called ________________ electrons. Because the σ1s MO is lower in energy than the H 1s atomic orbitals, the H2 molecule is more _______________ than the two separate H atoms.
two; geometry
Every pair of bonded atoms shares one or more pairs of electrons. Each bond line we draw in a Lewis structures represents _________ shared electrons. In every σ bond one pair of electrons is localized in the space between the atoms. The appropriate set of hybrid orbitals used to form the σ bonds between an atom and its neighbors is determined by the observed _________________ of the molecule.
polarities; geometry
For a molecule consisting of more than two atoms, the dipole moment depends on both the ________________ of the individual bonds and the ________________ of the molecule.
Lewis structure; electron-domain; hybrid
How to Describe the Hybrid Orbitals Used by an Atom in Bonding Draw the ____________ _________________ for the molecule or ion. Use the VSEPR model to determine the ___________________________ geometry around the central atom. Specify the ______________ orbitals needed to accommodate the electron pairs based on their geometric arrangement.
electron domains; one; minimized; molecular geometry
How to Predict the Shapes of Molecules and Ions Using the VSEPR Model Draw the Lewis structure of the molecule or ion, and count the number of ______________ ______________ around the central atom. Each nonbonding electron pair, each single bond, each double bond, and each triple bond counts as ___________ electron domain. Determine the electron-domain geometry by arranging the electron domains about the central atom so that the repulsions among them are _________________. Use the arrangement of the bonded atoms to determine the _________________ __________________.
weaker
If the Cl2 molecule is compressed under higher and higher pressure, does the Cl−Cl bond become stronger or weaker?
single; double; triple
In almost all cases, _____________ bonds are σ bonds. A ______________ bond consists of one σ bond and one π bond, and a _______________ bond consists of one σ bond and two π bonds:
bond order
In molecular orbital theory, the stability of a covalent bond is related to its ____________ _____________.
differing; polar; nonpolar
In polar covalent bonds, electrons are shared unequally between atoms. The way we can tell if electrons are shared unequally is by looking at the electronegativities, or the degree to which an atom attracts electrons in a molecule, of the atoms involved. Because all of the bonds are between atoms with ___________________ electronegativities except for Si−Si, they are all ______________ except for Si−Si. Because the atoms in Si−Si are identical, they have the same electronegativity values, attracting electrons to the same degree and making the bond __________________.
internuclear; sigma
In the covalent bonds we have considered thus far, the electron density is concentrated along the line connecting the nuclei (the ___________________ axis). The line joining the two nuclei passes through the middle of the overlap region, forming a type of covalent bond called a _____________ (σ) bond. Examples of sigma bond formation include: the overlap of two s orbitals; one from each H in H2 the overlap of an H s orbital and a Cl p orbital in HCl the overlap of two p orbitals; one from each Cl in Cl2 the overlap of an F p orbital and a Be sp hybrid orbital in BeF2
sulfurous
In the structure of __________________ acid, H2SO3, the central sulfur atom breaks the octet rule by having 10 valence electrons.
share; covalent
In valence-bond theory, we visualize the buildup of electron density between two nuclei as occurring when a valence atomic orbital of one atom shares space, or overlaps, with a valence atomic orbital of another atom. The overlap of orbitals allows two electrons of opposite spin to ____________ the space between the nuclei, forming a ________________ bond.
electrons
It turns out that ozone, O3, has a small dipole moment. How is this possible, given that all the atoms are the same? A: The lone pair of ________________ of the central O atom is the source of the dipole moment in O3.
shapes
Lewis structures do not show one of the most important aspects of molecules—their overall _____________. The shape and size of molecules—sometimes referred to as molecular architecture—are defined by the angles and distances between the nuclei of the component atoms.
two; opposite; definite; contour; entire
Molecular orbitals have many of the same characteristics as atomic orbitals. For example, an MO can hold a maximum of ____________ electrons (with _________________ spins), it has a ________________ energy, and we can visualize its electron-density distribution by using a _______________ representation, as we did with atomic orbitals. Unlike atomic orbitals, however, MOs are associated with an ________________ molecule, not with a single atom.
delocalized
Molecules can have π systems that extend over more than two bonded atoms. Electrons in extended π systems are said to be "___________________." We can determine the number of electrons in the π system of a molecule using the procedures we discussed in this section.
single
Note that the two regions of overlap in the π bond, above and below the internuclear axis, constitute a _____________ π bond.
different
Note that this molecule has two different constituent atoms bonded to the central atom and has an asymmetrical structure. Because the constituent atoms have _________________ electronegativities, there is an unbalanced distribution of electrons.
decrease; increases; more; space; repulsive; compress
Notice that the bond angles _______________ as the number of nonbonding electron pairs ________________. A bonding pair of electrons is attracted by both nuclei of the bonded atoms, but a nonbonding pair is attracted primarily by only one nucleus. Because a nonbonding pair experiences less nuclear attraction, its electron domain is spread out ____________ in space than is the electron domain for a bonding pair. Nonbonding electron pairs therefore take up more ____________ than bonding pairs; in essence, they act as larger and fatter balloons in our analogy. As a result, electron domains for nonbonding electron pairs exert greater ________________ forces on adjacent electron domains and tend to ________________ bond angles.
allotrope
One of two or more different molecular forms of an element in the same physical state
asymmetrical; nonpolar; planar; domains
Polar molecules require an _______________________ geometry and polar bonds. The trigonal pyramidal geometry of NH3 and seesaw geometry of TeF4 meet these requirements. Although the tetrahedral geometry is typically symmetrical, it becomes asymmetrical when the atoms attached to the central atom are not identical, which is why CH3F is polar. A completely symmetrical molecule would be _________________ whether or not it contains polar bonds. Molecules with ________________ geometries are therefore nonpolar: GaH3 (trigonal planar) and XeF4 (square planar). The tetrahedral geometry is symmetrical when all attached atoms are identical, which is why CI4 is nonpolar. All of these molecules are neutral, so you would identify their molecular geometries by determining how many bonding and lone-pair ________________ each central atom had (given that the attached atoms also have no formal charge in each case).
bond polarity; dipole moment
Recall that ___________ ______________ is a measure of how equally the electrons in a bond are shared between the two atoms of the bond. As the difference in electronegativity between the two atoms increases, so does the bond polarity. We saw that the _____________ _______________ of a diatomic molecule is a measure of the amount of charge separation in the molecule.
increase; decrease
Recall that for a given arrangement of ions, the lattice energy increases as the charges on the ions __________________ and as their radii _________________.
out; away
Regular lines imply the bond is the plane of the paper, a heavy wedge is used to show that the bond is coming _________ of the paper toward you, and the dashed line is used to show that the bond is pointing ____________ from you, through the back of the paper.
greater; axial; equatorial; less; equatorial
Repulsion between two domains is much _______________ when they are situated 90° from each other than when they are at 120°. An equatorial domain is 90° from only two other domains (the ____________ domains), but an axial domain is 90° from three other domains (the ___________________ domains). Hence, an equatorial domain experiences ____________ repulsion than an axial domain. Because the domains from nonbonding pairs exert larger repulsions than those from bonding pairs, nonbonding domains always occupy the _____________________ positions in a trigonal bipyramid.
larger
S2− is larger than K+ because the two ions are isoelectronic and K+ has the _______________ Z and Zeff.
family
S2− is larger than O2− because for particles with like charges, size increases going down a ____________.
zero; not
The 1s orbital is shaped like a sphere. Recall that nodal planes are regions where electron density is ____________. Spheres are uniform shapes that do not contain nodal planes. The 1s orbital does ___________ have a nodal plane.
lower; greater; lower; higher; two
The 2s atomic orbitals are substantially ____________ in energy than the 2p atomic orbitals. Consequently, both MOs formed from the 2s orbitals are lower in energy than the lowest-energy MO derived from the 2p atomic orbitals. The overlap of the two 2pz orbitals is ______________ than that of the two 2px or 2py orbitals. As a result, the bonding σ2p MO is _____________ in energy than the π2p MOs, and the antibonding σ∗2p MO is ______________ in energy than the π∗2p MOs. Both the π2p and π∗2p MOs are doubly degenerate; that is, there are ___________ degenerate MOs of each type.
nonplanar; polar
The PH3 molecule is polar. Does this offer experimental proof that the molecule cannot be planar? Explain. A: The molecule is ___________________. Thus, the P−H bond dipoles do not cancel, making the molecule ____________.
higher
The ______________ the bond order, the more stable the bond.
molecular geometry; electronic geometry
The ________________ ________________ of a molecule describes the three-dimensional shape of just the atoms. This is in contrast to the __________________ ________________, which describes the shape of all electron regions. To determine the molecular geometry of a molecule, one must first determine the electronic geometry by drawing the Lewis structure.
trigonal bipyramid; same; triangles
The ________________ ________________ shape for AB5 can be thought of as a trigonal planar AB3 arrangement with two additional atoms, one above and one below the equilateral triangle. The octahedral shape for AB6 has all six B atoms at the _____________ distance from atom A with 90°B—A—B angles between all neighboring B atoms. Its symmetric shape (and its name) is derived from the octahedron, with eight faces, all of which are equilateral __________________.
repulsions
The best arrangement of a given number of electron domains is the one that minimizes the __________________ among them.
polar covalent; 0.4; 2
The bonding predicted by electronegativities in PCl3 is ______________ _________________. The electronegativity difference between P (2.1) and Cl (3.0) is 0.9, which is a value below 1.8, but above 0.4, predicting a polar covalent bond. A nonpolar covalent bond would have an electronegativity difference less than __________. An ionic bond would have an electronegativity difference greater than _________.
lower; lower
The effective nuclear charge of an atom or ion affects the relative energies of the σ2p and π2p orbitals. Molecules for which π2p is _____________ than σ2p include Li2, Be2, B2, C2, and N2. In contrast, O2, F2, and He2 have a different molecular orbital arrangement, with σ2p _____________ than π2p.
lower; bonding molecular orbital; bonding molecular orbital
The energy of the resulting MO is ____________ in energy than the two atomic orbitals from which it was made. It is called the _________________ ___________________ _________________. A molecular orbital in which the electron density is concentrated in the internuclear region. The energy of a bonding molecular orbital is lower than the energy of the separate atomic orbitals from which it forms.
stronger; plane
The following statements regarding the bonding in the ethylene molecule, C2H4, are true: The C - C σ bond formed by the overlap of two sp2 hybrid orbitals is _________________ than the C - C π bond formed by the overlap of the unhybridized 2p orbitals. In order to form a π bond, the sp2 hybrid orbitals of the two carbon atoms must lie in the same _____________.
stronger
The greater the orbital overlap in a bond, the _______________ the bond.
stability; not; nuclear charge; overlap
The high bond order of the molecule helps explain its exceptional _______________. We should also note, however, that molecules with the same bond orders do ___________ have the same bond distances and bond enthalpies. Bond order is only one factor influencing these properties. Other factors include _______________ ______________ and extent of orbital _________________.
sp3d; trigonal bipyramidal
The hybridization of I3− is _____________. Look at the Lewis structure of I3− to determine that the electron group geometry around the central atom is trigonal bipyramidal. Molecules with ________________ ______________________ electron group geometry have sp3d hybridization.
unpaired; unpaired
The magnetic properties of B2 are consistent with the π2p MOs being lower in energy than the σ2p MO. The magnetic properties of a molecule reveal whether it has ________________ electrons. If the sigma_2p MOs are lower in energy, Br2 has no unpaired electrons. If the pi_2p MOs are lower in energy than the sigma_2p MO, there are two unpaired electrons. The magnetic properties of Br2 must indicate that it has _________________- electrons.
trigonal bipyramid
The most stable electron-domain geometry for five electron domains is the _______________ _________________ (two trigonal pyramids sharing a base).
octahedron; 90; equivalent; pyramidal; planar
The most stable electron-domain geometry for six electron domains is the ___________________. An octahedron is a polyhedron with six vertices and eight faces, each an equilateral triangle. An atom with six electron domains around it can be visualized as being at the center of the octahedron with the electron domains pointing toward the six vertices. All the bond angles are _________°, and all six vertices are __________________. Therefore, if an atom has five bonding electron domains and one nonbonding domain, we can put the nonbonding domain at any of the six vertices of the octahedron. The result is always a square-_________________ molecular geometry. When there are two nonbonding electron domains, however, their repulsions are minimized by pointing them toward opposite sides of the octahedron, producing a square-________________ molecular geometry
equals; similar; lowered; raised; two; one
The number of MOs formed _____________ the number of atomic orbitals combined. Atomic orbitals combine most effectively with other atomic orbitals of _____________ energy. The effectiveness with which two atomic orbitals combine is proportional to their overlap. That is, as the overlap increases, the energy of the bonding MO is ________________ and the energy of the antibonding MO is ______________. Each MO can accommodate, at most, ____________ electrons, with their spins paired (Pauli exclusion principle). When MOs of the same energy are populated, ____________ electron enters each orbital (with the same spin) before spin pairing occurs (Hund's rule).
equals
The number of standard atomic orbitals ____________ the number of hybrid atomic orbitals.
properties
The shape and size of a molecule of a substance, together with the strength and polarity of its bonds, largely determine the _______________ of that substance.
angles; bond lengths
The shape and size of molecules—sometimes referred to as molecular architecture—are defined by the ____________ and ____________ ______________ between the nuclei of the component atoms.
electron domains
The shapes of different ABn molecules or ions depend on the number of _______________ ______________ surrounding the central atom.
pi; weaker; weaker
The sideways overlap of p orbitals produces what is called a _______ (π) bond. A π bond is one in which the overlap regions lie above and below the internuclear axis. Unlike a σ bond, in a π bond the electron density is not concentrated on the internuclear axis. Although it is not evident in Figure 9.20, the sideways orientation of p orbitals in a π bond makes for ______________ overlap. As a result, π bonds are generally _______________ than σ bonds.
electron-domain geometry
The three-dimensional arrangement of the electron domains around an atom according to the VSEPR model.
degenerate
These two π2p molecular orbitals have the same energy; in other words, they are ________________. Likewise, we get two degenerate π∗2p antibonding MOs that are perpendicular to each other like the 2p orbitals from which they were made. These π∗2p orbitals have four lobes, pointing away from the two nuclei
VSEPR model
Valence Shell Electron Pair Repulsion model, which is based on an arrangement that minimizes the repulsion of shared and unshared pairs of electrons around the central atom
lower; stable; higher; stable
We therefore expect the σ2p MO to be ______________ in energy (more ____________) than the π2p MOs. Similarly, the σ∗2p MO should be ______________ in energy (less _____________) than the π∗2p MOs.
kJ/mol
What are the units of electron affinity?
between
What would you predict for the lengths of the bonds in NO2− relative to N−O single bonds and double bonds? A: The average of the two resonance structures for NO2− shows that both bonds in the molecule have partial single bond character and partial double bond character. This means we would expect the bond length to be somewhere in _________________ the length of a typical N−O single bond and a typical N=O double bond.
identical; only
When all the electron domains in a molecule arise from bonds, the molecular geometry is _______________ to the electron-domain geometry. When, however, one or more domains involve nonbonding pairs of electrons, we must remember that the molecular geometry involves ___________ electron domains due to bonds even though the nonbonding pairs contribute to the electron-domain geometry.
internuclear
When atoms share more than one pair of electrons, one pair is used to form a σ bond; the additional pairs form π bonds. The centers of charge density in a π bond lie above and below the __________________ axis.
two
Whenever two atomic orbitals overlap, __________ molecular orbitals form
same; different
Whenever we mix a certain number of atomic orbitals, we get the _____________ number of hybrid orbitals. Each hybrid orbital is equivalent to the others but points in a ________________ direction. Thus, mixing one 2s and one 2p atomic orbital yields two equivalent sp hybrid orbitals that point in opposite directions.
Cs
Which element in the periodic table has the smallest ionization energy?
C2H2; enthalpy
Which of the following molecules has the largest carbon - carbon bond enthalpy? C2H6, C2H4, or C2H2? The strongest bond has the largest bond ________________.
Kr
Which will experience the greater effective nuclear charge, the electrons in the n=3 shell in Ar or the n=3 shell in Kr?
O3
With what allotrope of oxygen is NO2− isoelectronic?
Delocalization; stability; plane; rigidity
______________________ of the electrons in its π bonds gives benzene a special ________________. Electron delocalization in π bonds is also responsible for the color of many organic molecules. A final important point to remember about delocalized π bonds is the constraint they place on the geometry of a molecule. For optimal overlap of the p orbitals, all the atoms involved in a delocalized π bonding network should lie in the same ______________. This restriction imparts a certain ______________ to the molecule that is absent in molecules containing only σ bonds.
valence-bond theory
a model of chemical bonding in which an electron-pair bond is formed between two atoms by the overlap of orbitals on the two atoms
antibonding molecular orbital
a molecular orbital in which electron density is concentrated outside the region between the two nuclei of bonded atoms
sigma molecular orbital; asterisk
a molecular orbital that centers the electron density about an imaginary line passing through two nuclei The bonding sigma MO of H2 is labeled σ1s; the subscript indicates that the MO is formed from two 1s orbitals. The antibonding sigma MO of H2 is labeled σ∗1s (read "sigma-star-one-s"); the ________________ denotes that the MO is antibonding.
dipole moment
a property of a molecule whose charge distribution can be represented by a center of positive charge and a center of negative charge
molecular orbital theory
a theory that accounts for the allowed states for electrons in molecules
paramagnetism
a type of induced magnetism, associated with unpaired electrons, that causes a substance to be attracted into the inducing magnetic field
diamagnetism
a type of magnetism, associated with paired electrons, that causes a substance to be repelled from the inducing magnetic field
molecular orbital
an allowed state for an electron in a molecular
hybrid orbitals
an orbital that results from the mixing of different kinds of atomic orbitals on the same atom
bonding; anti bonding
bond order = 1/2(number of __________________ electrons - number of _________________________ electrons
destructive combination
combining the two atomic orbitals in a way that causes the electron density to be canceled in the central region where the two overlap
homonuclear
containing atoms of only one element
tetrahedral
electron geometry of H2O:
pi molecular orbitals
electron probability lies above and below the line between the nuclei
Isoelectronic
having the same number of electrons
molecular orbital theory; atomic orbitals; molecular orbital
some aspects of bonding are better explained by a more sophisticated model called _________________ _________________ _______________. Electrons in atoms can be described by wave functions, which we call ______________ _________________. In a similar way, molecular orbital theory describes the electrons in molecules by using specific wave functions, each of which is called a ________________ ______________.
molecular geometry
the arrangement in space of the atoms of a molecule
bond dipole
the dipole moment that is due only to unequal electron sharing between two atoms in a covalent bond
hybridization
the mathematical mixing of different types of atomic orbitals to produce a set of equivalent hybrid orbitals
localized
the sigma and pie bonds are associated totally with the two atoms that form the bond