Chapter 10
The Lewis strucutre for the cyanide ion is shown. The formal charge on the C atom is equal to _____ and the formal charge on the N atom is equal to ______.
-(-1) -(0)
The Lewis structure for one of the resonance forms of the Sulfate Ion, SO4^2- is shown. WHat is the approximate value of the marked O-S-O bond angle?
-109.5 --although this structure appears to be flat with right angles between atoms, the true shape is tetrahedral because there are 4 electron groups.
The bond angle is the angle formed by the nuclei of _____ surrounding atoms with the nucleus of a central atom. THe bond angle predicted from the molecular shape is a(n) ________ bond angle. If the bonding electron groups around the central atom are not ______, the real bond angle will deviate from the predicted value.
-2 -ideal -identical
Describe how to draw a Lewis Structure
-A Lewis structure includes all the valence electrons in the species -A single bond contains two electrons and is represented by a solid line -An electron is added to the total count for each negative charge on the species
Describe the relative stabilities of resonance forms
-A resonance structure is more stable if a negative charge resides on a more electronegative atom -a resonance structure with smaller formal charges on individual atoms is preferred
Describe resonance structure
-An individual resonance structure does not accurately represent the structure of the species -Resonance structures differ only in the arrangement of electrons
In a Lewis Structure
-Bonding electron pairs are shown as lines -Lone pairs are shown as pairs of dots
Describe the "normal" bonding pattern for a neutral atom of each element, assuming that the octet rule is obeyed.
-F always forms a single covalent bond -H forms one covalent bond and is generally not found as a central atom in covalent species -C usually forms four covalent bonds.
Which species has a net dipole moment (are polar overal)
-NBr3 -CH2Cl2
Describe the effect of molecular polarity on the behavior of a molecular compound
-The physical properties of a molecular compound are directly related to the molecular polarity -a polar compound will experience stronger intermolecular forces than nonpolar compound
Which of the following options correctly describe the bonding and geometry in the anion SeCL5-
-There is one lone pair associated with the Se atom -This species is square pyramidal -there are six electron groups around the Se atom
The nitrite ion, NO2- is a resonance hybrid and has two resonance forms. describe the bonding in this species
-Two electron pairs are delocalized over the entire species. -Each N-O bond is a partial double bond. -The bond order for this species is 1.5
Steps for determining the shape of a covalently bonded species
-Use the molecular formula to draw a Lewis structure -count all electron groups and assign an electron group arrangement -determine the molecular shape by counting bonding groups and nonbonding groups seperately
The angle formed by the nuclei of two surrounding atoms with the nucleus of the central atom in a structure is called a(n) _____ angle. The value predicted for such an angle using the VSEPR theory would be 180 degrees, based upon geometry alone. This is referred to as the _______ bond angle. In practice, this value often deviates from the predicted value for various reasons.
-bond -ideal
In a single, double, or triple bond the shared electron pairs are localized between the bonded atoms. In a resonance hybrid, electrons are ________ or spread out over two or more adjacent atoms. Instead of a double or triple bond between two such atoms, the bond is considered a(n) _____ double or triple bond, with fractional bond order.
-delocalized -partial
Some elements do not obey the octet rule because they have more than eight valence electrons, they have a ________ valence shell. This is only possible for elements that have available ______ orbitals, elements from period ______ of the periodic table onward.
-expanded -d -3
Molecular shape is determined by the number of electron groups around a central atom, where a "group" consists of any number of electrons that occupy a _____ region around an atom. A double bond contains______ electron pairs but is considered _____ electron group because these electrons remain near eachother.
-localized -2 -1
Consider the molecule CCl4. each C-Cl bond in this molecule is _____ because the electronegativity difference between C and Cl is _____ than 0.4. Since CCl4 is tetrahedral in shape and symmetrical, the individual bond dipoles ______ and the molecule is ______ overall
-polar =greater -cancel -nonpolar
A structure containing a central atom surrounded by three electron groups will have a _______ planar arrangement in which the ideal bond angle is ______
-trigonal -120
Some covalently bonded species do not obey the octet rule because they have an odd number of electrons. A species containing one or more ____ electrons is called a free radical. Most odd-electron molecules have a central atom from an odd-numbered group, either group_____ or group ______
-unpaired -5A 7A
A molecule that contains covalent bonds and has a(n) _______ arrangement of electron groups will have an overall ______ polarity, which is measured as a dipole____
-unsymmetrical -molecular -moment
The formal charge assigned to an atom is calculated by subtracting the number of electrons the atom "owns" from the total number of _____ electrons. The number of electrons "owned" by a specific atom is defined as being the sum of the _____ valence electrons and half the _____ valence electrons.
-valence -unshared -shared
Arrange the following resonance forms in order of increasing importance in terms of their contribution to the overall structure, starting with the least important form at the top of the list. C=2.5 S=2.5 N=3.0
A, C, B
Which of the following elements, when covalently bonded, commonly have fewer than an octet of electrons with a formal charge of zero?
B, Be
Which of the following structures are not valid resonance forms for the sulfite ion So3^2?
B,C
Why is BeF2 a nonpolar molecule?
BeF2 is linear and therefore the individual bond dipoles cancel to give no net dipole
Which of the following is the correct Lewis Structure for the Hydronium Ion H3O+?
C
principle of VSEPR theory
Each group of valence electrons around a central atom is located as far from the others as possible.
Consider the molecules: SCl2, F2, CS2, CF4, and BrCl. Select the choice where the bonds of the molecules are arranged in order of increasing polarity.
F-F = C-S < Br-Cl < S-Cl < C-F
Any molecule in which all of the bonds are identical will be nonpolar.
False. For a molecule to be nonpolar, all bond dipoles must cancel and electron distribution must be symmetrical througout. A molecule with identical bonds will still be polar if the individual bond dipoles do not cancel. This may occur if there are one or more lone pairs on the central atom. As an example, water contains only O-H bonds but has an overall dipole moment because of its two lone pairs on the central oxygen.
Resonance structures are different possible structures for the same species that interconvert rapidly
False. No individual resonance form actually exists and there is no inter conversion between forms. Rather the true structure is a single structure that is an average of all possible resonance forms.
Half the shared bonding electrons are assigned to each atom of the bond in order to calculate
Formal Charge
When are multiple bonds needed in a Lewis Structure?
If one or more atoms do not have an octet of electron but all electrons have already been placed.
Define resonance structure
Lewis structures for the same species that differ in the placement of electrons
Formal Charge
May change for a particular atom from one resonance form to another
All shared bonding electrons are assigned to the more electronegative atom in order to determine
Oxidation Number
Which of the following elements may have an expanded valence shell?
S, Ce, Xe -must be beyond PERIOD 3 in order to expand.
Be sure to answer all parts. Determine the shape, the ideal bond angle, and the direction of any deviation of the following: TeF5−
Shape-square pyramidal angle-90* Direction of deviation-less than ideal
AX3E2
T-shaped
What change must be made to correct the Lewis structure shown for Carbon Monoxide?
Two lone pairs from oxygen must be used to form a triple bond.
The electron-group arrangement around a central atom is defined by the number of _____-electron groups. The molecular shape is defined by the relative positions of the ____ around the central atom
Valence atoms
Be sure to answer all parts. Dinitrogen difluoride, N2F2, is the only stable, simple inorganic molecule with an N=N bond. The compound occurs in cis and trans forms. (a) Select which of the molecular shapes of N2F2 correspond to the cis and trans form of N2F2. I h5a II h5b III h5c cis−dinitrogen fluoride: I II III trans−dinitrogen fluoride: I II III
a) Cis= 2 Trans=3 b)Cis=polar Trans=nonpolar
Arrange the following ACln species in order of decreasing Cl-A-Cl bond angles: SCl2, OCl2, PCl3, SiCl4, SiCl62− Which has the largest bond angles? SiCl62− SCl2 OCl2 SiCl4 PCl3 Which has the smallest bond angles? OCl2 SCl2 PCl3 SiCl62− SiCl4
a) SiCl4 b)SiCl6^2-
Determine the shape, the ideal bond angle, and the direction of any deviation of the following: IF4− Shape: tetrahedral octahedral square planar Ideal bond angle: degrees Direction of deviation (if any): greater than ideal less than ideal ideal
a) Square planar b) 90* c) Ideal
What would you expect to be the electron-group arrangement around atom A in the following case? Give the ideal bond angle and the direction of any expected deviation. X | X- A: | X a)Electron-group arrangement: *trigonal pyramidal *bent (V-shaped) *tetrahedral b)Ideal bond angle: _________° c)Expected angle deviation: *none *smaller *larger
a) Tetrahydral b) 109.5 c) Smaller
Determine the shape of the central atoms of the following molecule. N2O3 (ONNO2) (a) Shape around N(1) (ON): trigonal pyramidal bent (V-shaped) trigonal planar tetrahedral (b) Shape around N(2) (NO2): bent (V-shaped) trigonal planar trigonal bipyramidal tetrahedral
a) bent(v-shaped) b) trigonal planar
Determine the electron-group arrangement, molecular shape, and ideal bond angle for the following molecule: N2O (N is central) a) Electron-group arrangement: linear octahedral square pyramidal seesaw b) Molecular shape: linear T-shaped square pyramidal seesaw c) Ideal bond angle: degrees
a) linnear b) linnear c) 180*
Be sure to answer all parts. Determine the shape around each central atom of the following molecule and identify any deviation from ideal bond angles: CH3−O-CH2CH3 (a) Shape around the carbons: bent (V-shaped) trigonal pyramidal tetrahedral trigonal planar Direction of deviation (if any): ideal greater than ideal less than ideal (b) Shape around the O: tetrahedral T-shaped trigonal bipyramidal bent (V-shaped) Direction of deviation (if any): less than ideal greater than ideal ideal
a)tetrahydral b)ideal C)bent (v-shaped) d)less than ideal
Be sure to answer all parts. Determine the shape, the ideal bond angle, and the direction of any deviation for SeOF2. Molecular shape: bent trigonal pyramidal tetrahedral Ideal bond angle: degrees Direction of deviation: less than ideal ideal greater than ideal
a)trigonal pyramidal b)109.5 c)
Which of the lettered options corresponds to equatorial positions in the image shown?
b, c, d
AX2E2
bent
A
central atom in structure
Oxidation Number
does not change for a particular atom from one resonance form to another
The formal charge of an atom in a Lewis structure is the charge the atom would have if all bonding electrons were shared ______ between the atoms. The formal charge does not necessarily reflect an actual charge on the atom
equally
AX2E3
linear
Which of the following options correctly designate and describe the molecular shape around carbon for the molecule shown?
linear shape Designation AX2
E
nonbonding valence-electron group
m
number of bonding electron groups
n
number of nonbonding electron groups
Ax6
octahedral
AX4E
seesaw
AX4E2
square planar
AX5E
square pyramidal
X
surrounding atom
Ax4
tetrahedral
AX5
trigonal bipyramidal
AX3E
trigonal pyramidal