Chem Chapter 10

Which of the following molecules has at least one bond angle of 120°? Select all that apply.

CH2O trigonal planar 3 atoms attached to the central atom (O) PCl5 5 atoms attached to the central atom

Which of the species in the following list have a net dipole moment (i.e., are polar overall)? Select all that apply.

CHCl3 NBr3 03

What geometry and bond angles are associated with a molecule with geometry designated as AB5?

90° bond angles 120° bond angles Trigonal bipyramidal

ABxEy

A central atom B surrounding atom X # of bonding electrons groups x typically has values from 2-6 E lone pair y # of lone pairs

To classify geometry, a structure is assigned a specific ABx designation. Which of the following options correctly identify A, B, and x? Select all that apply.

A is the central atom in the structure. B designates a surrounding atom. x typically has values from 2 through 6.

Polar molecule

A molecule having a dipole moment

Nonpolar molecule

A molecule having no dipole moment

Why are the terms "axial" and "equatorial" not used to describe the bonds in an octahedral system?

All six bonds are equivalent in an octahedral system.

Match the 3D representation for each 6-electron group system to the correct molecular shape.

Square Planar Octahedral Square Pyramidal

AB3E2

T-shaped

Which of the following options correctly describe the geometry and bond angles of the covalent species KrBr2 (krypton dibromide)?

The Br-Kr-Br bond angle is 180°. The shape is linear. KrBr2 has 3 lone pairs on the central atom.

Draw a Lewis structure for the molecule ClF3. Which of the following options correctly describe this structure? Select all that apply.

The bond angles are less than 90°. Cl is the central atom

Which of the following options correctly describe a dipole moment?

The dipole moment provides a quantitative measure of bond polarity. A dipole moment arises when a bond or a molecule has an uneven distribution of electron density.

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

There are 6 electron pairs around the central Se atom. There is one lone pair associated with the Se atom. This species has a square pyramidal geometry.

A B C D E

Trigonal bipyramidal tetrahedral triagonal planar linear octahedral

AB3E

Trigonal pyramidal

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

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

In order to determine whether a molecule is polar or nonpolar _______. (Select all that apply.)

a Lewis structure is typically needed the polarity of individual bonds should be determined by comparing the electronegativities of the bonded atoms

According to VSEPR theory, each group of valence electrons around a central atom will be located ____ each other as possible, in order to minimize repulsions.

as far apart as possible

Individual bond dipoles will cancel

for a species that has identical bonds and a symmetrical geometry.

Individual bond dipoles will not cancel

for a species with an unsymmetrical geometry.

Polar molecules have a dipole moment that is ____, whereas nonpolar molecules have a dipole moment that is ____.

greater than zero; zero

A species will be nonpolar overall

if individual bond dipoles cancel.

A species will be polar overall

if individual bond dipoles do not cancel.

If electrons are completely transferred between the bonded atoms, the bond will be

ionic

Lone pair - lone pair repulsion

is much stronger than lone / bonding or bonding / bonding

The bond angles in the covalent species shown are ____.

less than 90°

AB2E3

linear

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.

more; decrease

Identical atoms will share electrons equally between them, giving a _________ bond.

nonpolar covalent

A polar covalent bond results in a ___________ electron distribution.

nonuniform or uneven electron distribution.

A polar covalent bond _____.

occurs when the bonded atoms attract the shared electrons differently involves unequal sharing of electrons

Six electron pairs around a central atom form a(n) _____________ arrangement with bond angles of ______ degrees

octahedral 90

In the 6-electron group AB4X2 system the 2 lone pairs occupy positions _____, giving a _____ shape.

opposite each other; square planar

Consider the molecule CCl4. Each C-Cl bond in this molecule is _________because Cl and C have different electronegativities. Since CCl4 is tetrahedral in geometry and symmetrical, the individual bond dipoles _________and the molecule is ___________ overall

polar cancel/balance nonpolar

AB4E

seesaw

Wedge-dash format

straight slim lines are in the plane of the screen wedged line is forward in front of the screen plane dashed lines are behind and back to the plane of the screen

In general, the smaller the bond angle, the _____ the electron repulsions for the electron pairs concerned. In a 5-electron pair system, lone pairs prefer to occupy _____ positions because equatorial-equatorial repulsions are _____ than axial-equatorial repulsions.

stronger; equatorial; weaker

Axial groups

up / down vertical 90 degrees to the Equatorial group or the ring

When using VSEPR to predict the geometry of a covalent species, the first step is to count the ____ electron groups around the central atom.

valence

Which of the following statements correctly describes the basic principle of the VSEPR model?

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

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

Explain why BeF2 is a nonpolar molecule.

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. For a molecule that has polar bonds, the geometry must be known in order to predict the overall polarity. If the individual bond dipoles do not cancel, the molecule is polar.

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

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

Which of the accompanying depictions show the electron distribution in the H2O molecule correctly? Select all that apply.

A C

Which of the following would typically be included in a description of the geometry of a covalent species? Select all that apply.

Bond angles Arrangement of atoms in space relative to each other Bond lengths

Which of the following options correctly describe a covalent species that has 4 electron pairs around the central atom? Select all that apply.

If all 4 electron pairs are bonding pairs, the shape of the system is tetrahedral. The predicted bond angle for a system with 4 electron pairs is 109.5o. A bent shape is observed if there are 2 bonding pairs and 2 lone pairs.

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

In what way do lone pairs located on the central atom in a Lewis structure affect the geometry of the species? Select all that apply.

Lone pairs make it difficult to predict the value of bond angles accurately. Lone-pair electrons repel neighboring electron pairs more than bonding electrons do. Lone pairs occupy more space than bonding pairs.

When marking the polarity of an N-F bond, the crossed tail of the dipole arrow would be over the ____ atom and the arrow would point toward ____. (Electronegativity values are: F, 4.0; N, 3.0)

N; F Reason: Correct. F is the more electronegative element. The dipole arrow points toward the F, indicating that the bonding electrons are being pulled toward this atom. The crossed tail of the arrow is over the N atom, indicating that this atom has lower electron density.

Which of the following determines the geometry around a central atom in a Lewis structure?

The number of valence-shell electron pairs

True or false: Any molecule in which all of the bonds are identical will be nonpolar.

This is false Reason: Correct. For a molecule to be nonpolar, all bond dipoles must cancel and electron distribution must be symmetrical throughout. 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. Reason why it is not true is because: This is not correct and is a common misconception. For a molecule to be nonpolar, all bond dipoles must cancel and electron distribution must be symmetrical throughout. 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.

Which of the following statements correctly describe the rules used to govern the application of the VSEPR model

Valence Shell Electron Pair Repulsion -------------- Multiple bonds take up more space than single bonds. Multiple bonds are treated as single bonds.

dipole moment

a measure of the separation and magnitude of the positive and negative charges in polar molecules measure of the polarity

A molecule will be nonpolar overall if ______. (Select all that apply.)

all electron groups around the central atom are identical bonding groups the arrangement of bonding groups and lone pairs allows bond dipoles to cancel

AB2E2 and AB2E

bent or angular

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

bonding or shared nonbonding or lone pair

The polarity of a bond can be expressed in terms of its _________ moment (symbol μ), which is the product of the partial charge in the bond and the ___________between the bonded atoms.

dipole distance

Place the steps for determining the geometry of a covalently bonded species in the correct order. Start with the first step at the top of the list.

draw the lewis structure, considering only the electron pairs around the central atom count the total number of electron pairs around the central atom predict the geometry of the molecule predict the bond angles in the molecule

In a covalent bond between identical atoms, the electrons are shared _____________ between the atoms. If the atoms are not identical, the electron distribution is ______________so that the electrons are closer to one atom than the other. This type of bond is called a(n) ____________ covalent bond.

equally unequal polar

The molecule XeF4 _____. (Select all that apply.) (Note that F is the most electronegative element and Xe as a noble gas attracts electrons much less strongly than F.)

is nonpolar overall because bond dipoles cancel contains polar bonds

Lone pairs are associated with _____ atom(s), giving them _____ spatial distribution than bonding electrons. For this reason, lone pairs experience greater repulsion from neighboring lone pairs and bonding pairs.

one; more

A system with molecular geometry designated AB4 is ____ and has ideal bond angles of ____.

tetrahedral; 109.5°

When using VSEPR to predict the shape of a covalent species that has two or more resonance structures _____.

the VSEPR model can be applied to any one of them

A structure containing a central atom surrounded by 3 electron pairs will have a __________ planar electron arrangement in which the bond angle is ________degrees

trigonal 120

AB5

trigonal bipyramidal

the ___________ shell is the outermost electron-occupied shell in an atom.

valence

According to the VSEPR model, each pair 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