Chem 211 chapter 10 smartbook

Select the correct Lewis structure for HCN. (Lone pairs of electrons are omitted.)

H-C≡N

Which option correctly describes a covalent species that has four electron groups around the central atom? Select all that apply.

The ideal bond angle for a four-electron system is 109.5o. If all four electron pairs are bonding pairs, the shape of the system is tetrahedral. A bent shape is observed if there are two bonding pairs and two lone pairs.

Which of the following elements, when covalently bonded, commonly have fewer than an octet of electrons with a formal charge of zero? Select all that apply.

Boron Beryllium

Select the statements that correctly describe the limitations of Lewis structures and formal charges.

A single Lewis structure often cannot correctly represent a molecule. Formal charge rules sometimes do not choose the Lewis structure arrived at by quantum mechanics calculations.

Review the attached image of the 3D molecular shape representation of an AX3E2 molecule. What changes might be made to make it more realistic?

Arrange the three bonded atoms in a T shape with the two bond angles slightly less than 90°.

Which of the following structures is the correct 3D representation for a molecule or ion with a seesaw shape?

B

Which of the following is the correct Lewis structure for the hydronium ion, H3O+?

C

Molecular shapes are classified by assigning a specific AXmEn designation to a structure. Match each symbol in this designation with its correct meaning. A m n X E

Central atom in structure Number of bonding electron groups Number of nonbonding electron groups surrounding atom Nonbonding valence-electron group

The nitrite ion, NO2-, is a resonance hybrid and has two resonance forms, as shown. Select all the statements that correctly describe the bonding in this species.

Each N-O bond is a partial double bond. The bond order for this species is 1.5. Two electron pairs are delocalized over the entire species.

Which statement correctly describes the basic principle of VSEPR theory?

Each group of valence electrons around a central atom is located as far from the others as possible.

Which of the following statements correctly describe the "normal" bonding pattern for a neutral atom of each element, assuming that the octet rule is obeyed? Select all that apply.

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.

True or false: Resonance structures are different possible structures for the same species that interconvert rapidly.

False

When drawing Lewis structures it is useful to recall the "normal" bonding patterns of common elements. Match each element with the number of covalent bonds the neutral atom usually has if the octet rule is obeyed. C N O F

Four bonds Three bonds Two bonds One bond

The structure shown represents an atom surrounded by three bonds drawn using the wedge-dash format. Match each bond to the correct description. a b c

In the plane Behind the plane In front of the plane

Which of the following statements correctly describe KrBr2? Select all that apply.

Kr is surrounded by 3 lone pairs. Kr is surrounded by 5 electron pairs.

Which of the following options correctly defines resonance structures?

Lewis structures for the same species that differ in the placement of electrons

Which of the following statements correctly describe resonance structures? Select all that apply.

Resonance structures differ only in the arrangement of electrons. An individual resonance structure does not accurately represent the structure of the species.

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 a fractional bond order.

Shared, partial

A B C

Square planar Octahedral Square Pyramidal

Which of the following is NOT a correct 3D representation of a tetrahedral system?

Structure A

A covalent species such as the molecule H3NO has more than one central atom. Which of the following options correctly describe how to draw a Lewis structure for this species? Select all that apply.

The O atom will be bonded to both H and N. N and O are central atoms because both elements form more than one covalent bond. There will be three bonds to the N atom.

Which of the following statements correctly describe the effect of molecular polarity on the behavior of a molecular compound? Select all that apply.

The physical properties of a molecular compound are directly related to molecular polarity. A polar compound will experience stronger intermolecular forces than a nonpolar compound.

A given species has a bond order of 1 1/2. What does this fractional bond order indicate? Select all that apply.

The species is a resonance hybrid. The species contains delocalized electrons.

Match each five-electron group designation to the correct molecular shape. AX5 AX4E AX3E2 AX2E3

Trigonal Bipyramidal Seesaw T-shaped Linear

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.

According to VSEPR theory, each group of _______________electrons around a central atom will be located as far away from the others as possible in order to minimize electron-electron ________________.

Valence, Repulsion

Which of the following elements may have an expanded valence shell? Select all that apply.

Xe Cl S

Resonance structures are Lewis structures that have the same relative placement of _____ but a different arrangement of _____.

atoms; electrons

Which of the lettered options correspond to equatorial positions in the image shown? Select all that apply.

b c d

The arrangement of 5 electron groups around a central atom is trigonal _____________. This system has two different bond angles. Three groups lie in a trigonal plane around the central atom with bond angles of ____________________o while the other two groups lie above and below this plane, at an angle of o to the trigonal plane.

bipyramidal 120 90

To classify molecular shapes, a structure is assigned a specific AXmEn designation, where A is the _____________atom, X is a(n)_______________ atom, and E represents a(n) _____________valence electron group that is usually a lone______________ .

central, bonded, unshared, pair

Lone pairs and double bonds are more spread out in space than a bonding pair. The result is that they exert greater repulsion on bonding pairs that leads to a(n) ______.

decrease in the angle between bonding pairs

Which of the following options correctly designate and describe the molecular shape around carbon for the molecule shown? Select all that apply.

designation AX2 linear shape

Because lone pairs exert larger repulsions than those from bonding pairs, any ______ will occupy ______ positions in a trigonal bipyramidal arrangement to minimize the repulsions between electron groups.

lone pairs; equatorial

Six electron groups around a central atom form a(n)______________ arrangement with ideal bond angles of _______________°.

octahedral 90

Match each six-electron group designation to the correct molecular shape. AX6 AX5E AX4E2

octahedral Square pyramidal Square planar

Molecular polarity has a direct effect on the behavior of molecular compounds. The attractive forces between polar molecules are _____ than those between nonpolar molecules. It therefore takes _____ energy to separate polar molecules from each other, and a polar compound will have a _____ boiling point than a nonpolar compound of similar size.

stronger; more; higher

What approximate value will be observed for the bond angle marked in the structure shown? (Note that Lewis structures commonly do not reflect the actual shape of the species.)

less than 109.5°

Draw the Lewis structure for acetonitrile (CH3CN). Select all the correct statements that apply.

Nitrogen forms a triple bond. The chemical formula gives information about the relative arrangement of the atoms.

Why is BeF2 a nonpolar molecule?

BeF2 is linear and therefore the individual bond dipoles cancel to give no net dipole.

A structure containing a central atom with two electron groups, designated AX2, has a _____ shape with a bond angle of _____ degrees.

linear; 180

A 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, equal

Which of the following structures are NOT valid resonance forms for the sulfite ion, SO32-? Select all that apply.

B C

Which of the following Lewis structures correctly represents the structure of formaldehyde (CH2O)?

C

Which of the following Lewis structures gives the best representation for the molecule NO?

C

A covalent species such as the molecule CH3OH has more than one central atom. Which of the following options correctly describe how to draw a Lewis structure for this species? Select all that apply.

C almost always forms four bonds. Chemical formulas often impart information about atomic arrangements. C and O could be central atoms because both elements can form more than one covalent bond.

Which one of the two images is a correct 3D representation for a 4 electron group system?

Structure B

To show the bonding in a molecule or polyatomic ion, we can use a Lewis structure, which shows bonding electron pairs as ______ and any nonbonding electrons as ______.

lines; dots

The Lewis structure for one of the resonance forms of the sulfate ion, SO42-, is shown. What is the approximate value of the marked O-S-O bond angle?

109.5

Certain molecules are electron deficient, having fewer than __________________electrons around the central atom, which nonetheless has a formal charge of zero. Elements that commonly form electron deficient gaseous compounds are beryllium and________________ .

8, B

The Lewis structure for the AsF5 is shown. The approximate value of the bond angle marked "a" is equal to _____, whereas the approximate value of the bond angle marked "b" is equal to _____. (Remember that this species is NOT flat, as indicated by the wedged and dashed bonds.)

90°; 120°

Which of the following structures ARE valid resonance forms for the molecule sulfur dioxide (SO2)? Select all that apply. Note that formal charges have not been included in the given structures.

A D

Which of the following statements correctly describe how to draw a Lewis structure? Select all that apply.

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.

Which species has a net dipole moment (i.e., are polar overall)? Select all that apply.

CH2Cl2 NBr3

Arrange the steps involved in drawing a Lewis structure in the correct order, starting with the first step on top.

Count the valence electrons fro all atoms, and add or subtract electrons according to the charge. Place the atoms relative to each other. Place a bond between every pair of atoms, using two valence electrons for each bond. Distribute the remaining electrons in pairs to give each atoms an octet Form multiple bonds if all electrons have been used and any atom des not have an octet

Which of the following statements correctly describe how to determine whether a given molecule is polar or nonpolar? Select all that apply.

If a molecule contains no dipole moments across any bonds, it will be nonpolar. If the individual bond dipoles do not cancel, the molecule is polar. For a molecule that has polar bonds, the geometry must be known in order to predict the overall polarity.

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

What is the molecular shape of the molecule represented in the attached image?

Square pyramidal

Match each four-electron group designation with the correct molecular shape. AX4 AX3E AX2E2

Tetrahedral Trigonal Pyramidal Bent

Which of the following statements correctly describe limitations to the use of formal charges when selecting Lewis structures of species with exceptions to the octet rule? Select all that apply.

The rules do not always select the experimentally accurate structures for species with expanded valence shells. The rules do not always select the most important resonance structure for species with unpaired electrons (free radicals). The rules do not always select the same structure as that calculated by quantum mechanics.

Which of the following statements correctly describe how to determine molecular shape using the VSEPR model? Select all that apply.

The total number of shared and unshared electron pairs around the central atom gives the electron-group arrangement. Use the molecular formula to draw the Lewis structure.

Which of the following options correctly describe the bonding and geometry in the anion SeCl5-? Select all that apply.

There are six electron groups around the central Se atom. There is one lone pair associated with the Se atom. This species has a square pyramidal shape.

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

The molecular shape of a covalent species is determined not only by the number of _______________electron groups that join the atoms, but by the number of _______________electron groups as well, since these electrons also occupy space.

bonding, lone pair

Because lone pairs exert larger repulsions than those from bonding pairs, lone pairs will occupy________________ (equatorial/axial) positions in a trigonal bipyramidal arrangement to minimize repulsions between electron groups.

equatorial

A five-electron group system (shown) has two different types of positions for substituents. The three positions marked "1" form a trigonal plane about the central atom and are called _____ positions while the two positions marked "2" are _____ positions. Lone pairs prefer to occupy the _____ positions.

equatorial; axial; equatorial

Some elements do not obey the octet rule because they have more than eight valence electrons, i.e., they have a(n)____________ valence shell. This is only possible for elements that have available ________________orbitals, i.e., elements from period _______________of the periodic table onward.

expanded empty 3

Partial bonding, for example, as part of a resonance hybrid, often results in structures with _____.

fractional bond orders

The structure shown represents an atom surrounded by three bonds drawn using the wedge-dash format. The bond marked "a" is a bond _____ the plane, and the bond marked "b" is _____ the plane and the bond marked "c" is _____ the plane.

in; behind; in front of

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 pair(s) but is considered _____ electron group because these electrons remain near each other.

localized; two; one

In a Lewis structure, _______. (Select all that apply.)

lone pairs are shown as pairs of dots bonding electron pairs are shown as lines

In general, a lone pair repels bonding electron pairs _____ than bonding pairs repel each other. A lone pair will therefore _____ the bond angle between bonding pairs. A double bond has a similar effect because a double bond has a _____ electron density than a single bond.

more; decrease; greater

A Lewis structure will usually require one or more multiple bonds if there is an atom present that does not have a full _____________after all available electrons have already been placed. The multiple bond is formed by exchanging one __________________electron pair for each new bond.

octet, lone

Match each of the three-electron group systems with the correct molecular shape. AX3 AX2E

trigonal planar Bent

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

True or False: Two molecules with the same electron-group geometry can have different molecular shapes.

true

True or false: When using VSEPR theory to determine molecular shape, a triple bond counts as a single electron domain even though it consists of three shared electron pairs.

true

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. Two species may have the same electron-group arrangement but have different molecular shapes.

Valence, atoms

In general, the smaller the bond angle, the _____ the electron repulsions for the groups concerned. In a five-electron group system, lone pairs prefer to occupy _____ positions because equatorial-equatorial repulsions are _____ than axial-equatorial repulsions.

stronger; equatorial; weaker

What is the approximate H-C-H bond angle in the molecule shown?

little less than 120°

Which of the following is the correct Lewis structure for the molecule H3NO? Remember to take into account the normal bonding patterns for each of the elements.

B

Which of the following is the correct Lewis structure for the cation ICl2+?

A

Which of the following is the correct Lewis structure for the molecule OF2?

B