SB 10, Representing MoleculesAssignment
.._.. - [C=N] The Lewis structure 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
Given that the dipole moment of an HBr molecule is 0.82 D and the H-Br bond length is 1.41 angstroms, calculate the partial charges on the atoms in a molecule of HBr.
0.12 e-
The measured dipole moment of the O-H bond in gaseous water is 1.855 D and the bond length is 0.97 angstroms. Calculate the the partial charges on the atoms in this polar covalent bond.
0.40 e-
Arrange the necessary steps in order for finding the molecular formula of an unknown compound from mass percent data. Place the first step at the top of the list.
1. Assume that the sample contains 100.0 g of compound and express each mass percent as a mass in grams. 2. Convert the mass of each element to moles of each element. 3. Derive the empirical formula looking for the simplest whole-number ratio of moles. 4. Divide the molar mass of the compound by the mass of the empirical formula in order to find a multiple that is an integer. 5. Multiply each subscript of the empirical formula by the integer multiple.
Order the steps for drawing a correct Lewis structure for a molecule, beginning with the first.
1. Count the total number of valence electrons and draw the skeletal structure of the molecule. 2. Complete the octets of the terminal atoms using available electrons. Count each existing bond in the skeletal structure as two electrons. 3. Place any remaining electrons on the central atom. 4. If necessary to satisfy the octet rule, convert lone pairs on outlying atoms into one or more multiple bonds to the central atom.
Click and drag on elements in order Using the table of electronegativities provided arrange the following bonds in order of increasing ionic character. (Place the least polar bond at the top of the list.)
1. Pd-H 2. C-H 3. N-O 4. F-Cl
How many electrons are in the valence shell of the central atom of ICl3
10
Calculate the percent ionic character of the H-Cl bond if the observed dipole moment of HCl is 1.08 D and the bond length is 1.27 angstroms.
17.7%
Which of the following provides the correct mathematical operation to calculate the number of molecules in 2.0 mol of CH4?
2.0 mol × 6.022 × 1023 molecules/mol
Calculate the correct number of moles AND formula units in 7.3 x 10-3 g of CaSO4. Avogadro's number is 6.022 × 1023.
3.2 × 1019 formula units of CaSO4 5.4 × 10-5 moles of CaSO4
The percent ionic character of the H-F bond is 41.5%, and the observed dipole moment is 1.82 D. What would be calculated dipole moment of the bond, based on a complete separation of charge?
4.39 D
How many grams of KMnO4 correspond to 3.13 × 1022 formula units of KMnO4? Avogadro's number is 6.022 × 1023.
8.21 g of KMnO4
Which of the structures shown is the best Lewis structure for COCl2?
A :Ö || .. || .. :Cl ----- C ----- C: ** **
Which symbol correctly depicts the shift in electron density between the two atoms in an HCl molecule?
A H ----> Cl
Which of the structures shown is the best Lewis structure for COCl2?
A Ö || Cl -- C -- Cl
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 .. .. :Ö = S -- Ö: :Ö -- S = Ö: ** **
Select all the statements that correctly describe how to draw a Lewis structure.
A single bond contains 2 electrons and is represented by a solid line. A Lewis structure includes all the valence electrons in the species. An electron is added to the total count for each negative charge on the species.
Which of the following statements correctly defines a free radical?
A species with an odd number of valence electrons
Which of the following statements correctly describe formal charges and the skeletal arrangement of atoms in a Lewis structure? Select all that apply.
A structure in which all formal charges are zero is preferred to a structure containing nonzero formal charges. A structure in which nonzero formal charges are small is preferred to a structure in which they are large.
Which of the following statements correctly describe resonance structures? Select all that apply.
An individual resonance structure does not accurately represent the structure of the species. Resonance structures differ only in the arrangement of electrons.
Which structure shown is the correct Lewis structure for XeF4?
B .. :Xe: **
Which of the following is the correct Lewis structure for the molecule OF2?
B F--Ö--F **
Which image correctly represents the separation of charge between the atoms of an HBr molecule?
B δ+. δ- Η----Βr
Which of the following structures are NOT valid resonance forms for the sulfite ion, SO32-? Select all that apply.
B C O O | | [O=S-O]^2- [O = S = O]^2-
Which of the following molecules have a central atom with an incomplete octet? Select all that apply.
BF3 AlH3
Which of the following molecules have a central atom with an incomplete octet? Select all that apply.
BH3 BeCl2
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.
Beryllium Boron
The molecular formula of a compound having an empirical formula NH2 (ℳ = 32.05 g/mol) is N__________H_____________
Blank 1: 2 or two Blank 2: 4 or four
Certain molecules are electron deficient, having fewer than _____________ electrons around the central atom. Elements that commonly form electron deficient compounds are beryllium and ______________ . (One word answer.)
Blank 1: 8 or eight Blank 2: boron, B, Al, aluminum, or aluminium
A covalent bond in which both electrons are contributed by one of the two bonded atoms is called a ______________ covalent bond.
Blank 1: coordinate or dative
Elements that do not obey the octet rule because they have more than eight valence electrons are said to have an ______________ valence shell. This is only possible for elements that have available ________________ orbitals, which are the elements found from period ________________ of the periodic table onward.
Blank 1: expanded or extended Blank 2: d Blank 3: 3 or three
"Percent ionic character" is a means of comparing the _________________ dipole moment of a bond to the calculated value based on a complete separation of charges.
Blank 1: observed, actual, measured, or experimental
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.
Blank 1: octet, valence shell, outer shell, or outer level Blank 2: lone, non-bonding, nonbonding, unshared, nonbonded, non-bonded, or unbonded
An atom or molecule that contains an odd number of valence electrons is known as a free _____________.
Blank 1: radical
Which of the structures shown is the best Lewis structure for CH4O?
C H | H -- C -- Ö -- H | ** H
Which image correctly depicts the shift in electron density in the bonds of a CO2 molecule?
C <---- ----> O=C=O
Which pair of symbols is used to depict a partial separation of charge in a covalent bond?
C δ- δ+
Which image correctly represents the separation of charge between atoms in the molecule sulfur monoxide?
C δ- δ+ O=S
Select the correct Lewis structure for the molecule NO.
C .. *N = Ö:
Which of the following is the correct Lewis structure for the hydronium ion, H3O+?
C .. [H --O-- H] | H
When drawing Lewis structures it is useful to recall the "normal" bonding patterns of common elements (Sec. 5.2). Match each element with the number of covalent bonds the neutral atom usually has if the octet rule is obeyed. Instructions
C <--> 4 bonds N <--> 3 bonds O <--> 2 bonds F <--> 1 bond
A particular hydrocarbon (a compound consisting only of C and H) contains 14.4% H by mass. If the molar mass of the compound is 85. ± 2 g/mol, what is the molecular formula?
C6H12
A compound has the empirical formula CH2O. What are the possible options for the molecular formula of this compound? Select all that apply.
CH2O C6H12O6 C2H4O2
What symbol is used to indicate a shift in electron density between atoms in a polar covalent bond?
Crossed arrow
Match each term with its correct definition. Electronegativity: Electron affinity:
Electronegativity: The tendency of an atom of a given element to attract shared electrons to itself in a covalent bond Electron affinity: The energy released when an electron is added to an atom of a given element in the gas phase
True or false: Resonance structures are different possible structures for the same species that interconvert rapidly.
False
Which of the following statements correctly defines formal charge?
Formal charge compares the electrons associated with an isolated atom to the electrons associated with the atom in a covalent species.
Select all statements that correctly describe formal charge.
Formal charge is the comparison of an atom's associated electrons with its isolated valence electrons. Formal charge can be used to determine the most plausible Lewis structure for a given compound.
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? (See Sec. 5.2) Select all that apply.
H forms one covalent bond and is generally not found as a central atom in covalent species. C forms four covalent bonds. F forms a single covalent bond.
Using the table of electronegativity values provided, select all the bonds from the following list that are polar covalent. (Use the electronegativity difference guidelines specified in this text.)
H-O B-Cl C-N
Which of the following options correctly describe how formal charge is assigned to an atom in a Lewis structure? Select all that apply.
Half of an atom's bonding electrons are considered associated electrons. Formal charge = (valence electrons) - (number of associated electrons)
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
BF3 has some properties consistent with a complete electron octet on boron, and some properties consistent with an incomplete octet. Match the property with the valence shell it implies.
Incomplete octet <---> BF3 forms coordinate covalent bonds with molecules like NH3. Complete octet <---> The B-F bond length in BF3 is shorter than a single bond.
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 options correctly describe the general trends in electronegativity? Select all that apply.
Metals tend to have lower electronegativities than nonmetals. Electronegativity tends to decrease down a group of the periodic table. Fluorine is the most electronegative element.
Which molecule(s) contain(s) an odd number of valence electrons? Select all that apply.
NO NO2 OH
Match each compound to the manner in which the central atom violates the octet rule.
NO2 <---> Fewer than eight valence electrons due to an odd number of valence electrons SCl6 <---> More than eight valence electrons due to an expanded octet BeF2 <---> Fewer than eight valence electrons due to a shortage of valence electrons
Match each qualitative bond definition with the typical difference in electronegativity values between atoms. Instructions Nonpolar: Polar covalent: Ionic:
Nonpolar: Difference less than 0.5 Polar covalent: Difference between 0.5 and 2.0 Ionic: Difference of 2.0 or more
Which molecule(s) contain(s) an odd number of valence electrons? Select all that apply.
O2- ClO2 NO2
Consider the Lewis structures shown for the species SOCl2. Not all are possible resonance forms, and formal charges have been deliberately omitted from individual atoms. Select all the statements that correctly describe the structure of SOCl2.
S can use an expanded valence shell because it has available d orbitals. Structure B is preferred because all formal charges are zero.
Consider the phosphate ion, PO43-. Draw Lewis structures and assign formal charges for structures with: A) all single bonds or B) three single bonds and one double bond (note this gives rise to four equivalent resonance structures). Which of the following statements could chemists use to argue about which is the dominant structure? Select all the correct statements.
Structure B may be dominant because some data shows average bond length to be less than that for a single bond. Structure A may be dominant because all P and O atoms have an octet.
The boron halides (like BF3) may be represented by resonance Lewis structures with either all single bonds or one double bond and two single bonds (the latter gives rise to three equivalent resonance structures). Select the correct statements relating the Lewis structures to the observed properties. Select all that apply.
The Lewis structure containing all single bonds is consistent with their behavior as Lewis acids. The Lewis structures containing a B=X bond is supported by data showing bond lengths shorter than those of a single bond.
Which of the following is NOT involved in determining the empirical formula of a compound from mass percent data?
The molar mass of the compound
Draw the Lewis structure for NO2 and select the correct statements about the structure. Select all that apply.
The molecule gives rise to two equivalent resonance structures. The unpaired electron is placed on nitrogen. There are 17 valence electrons in NO2.
Which of the following would cause the central atom in a Lewis structure to have less than a full octet of electrons? Select all that apply.
The total number of valence electrons is odd. The species has a shortage of valence electrons.
What does the symbol ↔ mean when used between two chemical structures?
The two structures are resonance forms of the same species.
Which of the following elements may form an expanded valence shell? Select all that apply.
Xe Cl S
Calculate the formal charges on each of the nitrogen atoms in the N3- ion shown. The overall charge of the ion has been omitted in the structure.
a = -1; b = +1; c = -1
Resonance structures are Lewis structures that have the same relative placement of _____ but a different arrangement of _____.
atoms; electrons
A type of covalent bond in which one atom donates both of the electrons is called a(n) _____ bond.
coordinate coordinate covalent dative
In general, electronegativity ______ as atomic size increases because a shared electron pair is closer to the nucleus of a smaller atom, which therefore attracts these electrons ______ strongly. Thus, electronegativity tends to ______ from left to right across a period of the periodic table and tends to ______ down a group.
decreases, more, increase, decrease
Both electronegativity and electron affinity connote an atom's ability to attract electron's to itself. However, _____ addresses the atom in a chemical bond while _____ applies to the isolated atom.
electronegativity; electron affinity
Which one of the following options gives the correct procedure to calculate the number of moles of a substance given the mass of a sample?
mass/molar mass
The _____ formula of a compound is an integer multiple of the _____ formula.
molecular; empirical
Which one of the following options gives the correct procedure to calculate the mass of a substance given the number of moles?
moles x molar mass
Which of the following provides the correct mathematical operation to convert the number of atoms of a sample to the number of moles?
number of atoms x Avogadro's number
The value for a covalent bond obtained from the formula: μ(obs)/μ(calc) × 100 is called the ______.
percent ionic character
A bond between two atoms whose electronegativity values differ anywhere from 0.5 to 2.0 is considered ______; whereas a bond between atoms whose electronegativities differ by 2.0 or more is considered ______.
polar covalent, ionic
The dipole moment (μ) of a polar covalent bond is calculated as the _____ of the magnitude of the partial charges (Q) and the _____ between them.
product, distance
The formal charge assigned to an atom is calculated by subtracting the number of electrons associated with the atom from the total number of ______ electrons. The number of electrons associated with a specific atom is defined as being the sum of the ______ electrons and half the ______ electrons.
valence, unshared, shared
When more than one skeletal arrangement of atoms is possible in a Lewis structure, formal charges can help determine the best arrangement. For molecules, a Lewis structure in which all of the formal charges are ______ is preferred to one that contains ______ formal charges.
zero, nonzero
Which of the following is the correct formula for calculating the dipole moment of a polar covalent bond?
μ = Q × r
Which symbol is used to indicate that two Lewis structures are resonance forms of the same molecule?
↔
