CHM 115 Chapter 10 Flashcard

Place the steps for determining the shape of a covalently bonded species in the correct order. First step at the top of the list.
– 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 separately.
AX_6
Octahedral
AX_5E
square pyramidal
AX_4E_2
square planar
Certain molecules are electron deficient, having fewer than ___ electrons around the central atom. Elements that commonly form electron deficient gaseous compounds are beryllium and _____________.
8; boron
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, 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; non polar
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.
All shared bonding electrons are assigned to the more electronegative atom in order to determine
oxidation number
Oxidation number
Does not change for a particular atom from one resonance form to another.
Half the shared bonding electrons are assigned to each atom of the bond in order to calculate
formal charge
Formal charge
may change for a particular atom from one resonance form to another.
electron-group arrangement
defined by the bonding and nonbonding electron groups
Molecular shape
defined by the relative positions of the nuclei, which are connected by the bonding groups only.
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.
A molecule that contains covalent bonds and has a(n) _______ arrangement of electron groups will have an overall _____ polarity, which is measure as a dipole ______.
unsymmetrical; molecular; moment
Why is BeF2 a non polar molecule?
BeF2 is linear and therefore the individual bond dipoles cancel to give no net dipole.
Which of the following statements correctly describe how formal charge is assigned to an atom in a Lewis structure?
– Formal charge = (valence e-) – (unshared e- + 1/2shared e-)
– The number of shared electrons equals twice the number of bonds in the structure.
– The atom is considered to “own” half the shared electrons.
AX_4
tetrahedral
AX3E
trigonal pyramidal
AX2E2
bent
Which of the following statements correctly describe the effect of molecular polarity on the behavior of a molecular compound?
– The physical properties of a molecular compound are directly related to molecular polarity.
– A polar compound will experience stronger intermolecular forces than a non polar compound.
A resonance structure with more charges will be _____ stable than a resonance structure with fewer charges. For two resonance forms with the same formal charges, the resonance structure that has the negative formal charge on the more _________ atom will be more stable.
less; electronegative
Some covalently bonded species do not obay 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
AX5
trigonal bipyramidal
AX5E
seesaw
AX3E2
T-shaped
AX2E3
linear
Which of the following statements correctly describe formal charge?
– Formal charges can be used to select the most important resonance structures for a species.
– The formal charge of an atom is the charge it would have if all bonding electrons were shared equally.
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.
two; ideal; identical
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; surrounding; nonbonding; pair
Arrange the steps involved in drawing a Lewis structure in the correct order, starting with the first step on top.
– Count the valence electrons from all atoms, 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 atom an octet (except for hydrogen).
– Form multiple bonds if all electrons have been used and any atom does not have an octet.
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
Which of the following statements correctly 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.
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
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; d; 3
Place the steps for determining the shape of a covalently bonded species in the correct order. Start with the first step at the top of the list.
– 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 separately.
Lone pairs prefer to occupy the _____ positions.
equatorial
Which option correctly describes a covalent species that has four electron groups around the central atom?
– a bent shape is observed if there are two bonding pairs and two lone pairs.
– the ideal bond angle for a four-electron system is 109.5
– if all four electron pairs are bonding pairs, the shape of the system is tetrahedral.
Which of the following statements correctly describe how to determine whether a given molecule is polar or non polar?
– for a molecule that has polar bonds, the geometry must be known in order to predict the overall polarity.
– if a molecule contains no dipole moments across any bonds it will be non polar.
– if the individual bond dipoles do not cancel, the molecule is polar.
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
Which of the following statements correctly describe resonance structures?
– resonance structures differ only in the arrangement of electrons.
– an individual resonance structure does not accurately represent the structure of the species.
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.
shared; unshared
Which of the following options correctly defines resonance structures?
Lewis structures for the same species that differ in the placement of electrons.
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.
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.
delocalized; partial
Resonance structures are Lewis structures that have the same relative placement of _____ but a different arrangement of ______.
atoms, electrons
Which species has a new dipole moment (i.e., polar overall)? CO2, CH2Cl2, NBr3, BCl3, Cl2
CH2Cl2, NBr3
The polarity of a molecule can be expressed in terms of its _______ moment (symbol ?), which is the product of the partial _____ in the molecule and the ______ between their centers.
dipole; charges; distance
According to the 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? Cl, O, S, Xe, N
Cl, S, Xe
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 repulsion are ______ than axial-equatorial repulsions.
stronger, equatorial, weaker
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?
– there will be three bonds to the N atom
– N and O are central atoms because both elements form more than one covalent bond.
– The O atoms will be bonded to both H and N.
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
Axial group
An atom (or group) that lies above or below the trigonal plane of a trigonal bipyramidal molecule, or a similar structural feature in a molecule.
Equatorial group
An atom (or group) that lies in the trigonal plane of a trigonal bipyramidal molecule, or a similar structural feature in a molecule.

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