EXAM 4

25 July 2022
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question
How many valence electrons must be accounted for in the Lewis structure of chloroethane (C2H5Cl)? (4, #1)
answer
20
question
How many electrons should be shown in the Lewis symbol for hydrogen? (4, #1)
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1
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Rank the following elements in order of decreasing electronegativity (from most electronegative to least electronegative): (4,#3)
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Cl>S>Se>As
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If the difference in electronegativity (?EN) between two atoms is 1.5, how would the bond formed between those atoms be classified? (4,#3)
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a polar covalent bond
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What type of bond would you expect to form between NN and HH in ammonia, NH3? Electronegativity for N is 3.0 and for H is 2.1. (4,#3)
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polar covalent bond
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What is atomic radius?
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Atomic radius is one periodic property of the elements. Atoms become smaller from left to right across a row, but they become larger going down a column. The largest atoms are thus found in the bottom left corner of the periodic table.
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What is ionization energy?
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Ionization energy is another periodic property of the elements. The ionization energy of an atom is the energy required to remove an electron when the element is in a gaseous state. Ionization energies tend to increase from left to right across the row, but they decrease going down a column. The highest ionization energies are thus found in the upper right corner of the periodic table. Some sample ionization energies are shown in the table below.
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what is electron affinity?
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The electron affinity of atoms is also periodic. The electron affinity of an atom is the energy that is lost or gained when an electron is added to a neutral atom of the element in a gaseous state. A more negative electron affinity is considered a higher electron affinity value. It tends to become more negative going from left to right across a row in the table and less negative going down a column. Electron affinities are not as smoothly periodic as some of the other properties, with some major exceptions opposing the general trends. For example, the group 2 and group 18 elements have positive electron affinities, and each of the row 2 elements B through F are less negative than the elements just below them in the column. In general, however, electron affinities tend to be more negative as you move toward the upper right-hand corner of the periodic table.
question
A Venus probe detects an element with a first ionization energy of 2088 kJ/molkJ/mol. Given the table of known ionization energies provided in the introduction, what is the most likely identity of this element? (4,#4) Li- 520 kj/mol Cs-382 kj/mol He-2377 kj/mol Rn- 1042 kj/mol
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Ne
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Which element has the highest (most negative) electron affinity? (4,#4) Kr,Br,K,Be,Ni
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Br
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Determine whether a bond between each pair of atoms would be pure covalent, polar covalent, or ionic. (4, #5) Br and Br C and I Na and O N and O
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pure: Br and Br, C and I Polar covalent: N and O Ionic: Na and O
question
Resonance structures
Resonance structures
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to understand what resonance means and when it occurs. Three resonance structures can be drawn for NO3?(see the figure) because it is possible to have the double bond on any of the three oxygen atoms. (Figure 1) Here the total number of valence electrons in NO3? is 24 (5 valence electrons from nitrogen, 18 electrons from 3 oxygen atoms, and 1 electron from the single negative charge present in the molecule). All these resonance structures have 24 valence electrons. Which one is correct? Experiments show that all three bonds in nitrate have the same length. This indicates that the electrons of the double bond have become delocalized, or spread out over all three oxygen atoms. Therefore, each oxygen atom forms one and one-third bonds. The actual structure is an average of all three resonance structures, as shown in the second figure. (Figure 2)
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How many resonance structures can be drawn for ozone, O3? (4,#6)
How many resonance structures can be drawn for ozone, O3? (4,#6)
answer
2
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Which statement best describes an O3 molecule? -An ozone molecule contains one single bond and one double bond. -Each atom in ozone is connected to another atom by a bond having a bond order of 1.5. -The double bond in ozone switches back and forth between the two outer oxygen atoms. (4, #6)
answer
Each atom in ozone is connected to another atom by a bond having a bond order of 1.5.
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how to calculate formal charge ( 4, #6)
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(number of valence electrons in a free atom)?[(number of non-bonding electrons on the atom)+(1/2 Γ— number of bonding electrons)]
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Which resonance form is likely to contribute most to the correct structure of N2O? (4,#7)
Which resonance form is likely to contribute most to the correct structure of N2O? (4,#7)
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Structure B contributes the most to the correct overall structure of N2O because it minimizes the number of formal charges and the negative formal charge resides on oxygen, which is more electronegative than nitrogen.
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formal charges and resonance structures
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The interactive activity shows how to calculate the formal charge of atoms in a structure. These formal charges can be used to predict the resonance structure that contributes most to the stability of a molecule or ion. The structure with the lowest formal charge on each atom and which places the negative charge on the most electronegative atom is generally the most stable.
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What is the formal charge on the sulfur and oxygen atom in SO? (4,#8)
What is the formal charge on the sulfur and oxygen atom in SO? (4,#8)
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S= 0 O= 0
question
Which of these compounds could have a Lewis structure with an incomplete octet? (4,#10) PF5 PCl3 BCl3 CH4
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BCL3, Boron tends to form compounds with incomplete octets. BCl3 has three single bonds, and therefore three electron pairs, or 6 electrons, which is less than 8 and therefore represents an incomplete octet.
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Which of these polyatomic ions cannot have a Lewis structure with an expanded octet? (4,#10) ClO2? CO32? PO43? SO32?
answer
CO32- C is a second-row element and does not have energetically accessible d orbitals to form expanded octets. Thus, CO32? cannot have a Lewis structure with an expanded octet.
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How many electrons are assigned to the central SbSb atom in the Lewis structure for the compound SbF5? (4, #10)
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10. There are five bonds and thus pairs of electrons shared between F atoms and the central SbSb atoms, giving Sb 10 valence electrons.
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Bond orders
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Bond order corresponds to the type of bond. Single bonds have a bond order of 1, double bonds have a bond order of 2, and triple bonds have a bond order of 3. A higher bond order corresponds to higher bond energy for series of similar atoms. Therefore a carbon-carbon triple bond is stronger than a carbon-carbon double bond, which is stronger than a carbon-carbon single bond. A higher bond order corresponds to a shorter bond length for series of similar atoms as well. Therefore triple bonds are the shortest, and single bonds are the longest when comparing bonds between the same two atoms.
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What is the bond order of F?OF? (4, #11)
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1
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What is the bond order of O2? (4,#11)
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2
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What is the bond order of CO? (4, #11)
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3
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Rank the following series of molecules or ions in order of decreasing bond energy using their bond order to predict relative magnitude: oxygen difluoride: F?OF, oxygen: O2, carbon monoxide: CO (4,#11)
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CO>F-OF>O2
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Order these compounds in order of decreasing carbon-carbon bond strength. ( 4, #11)
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HCCH, H2CCH2, H3CCH3
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Order these compounds in order of decreasing carbon-carbon bond length. (4,#12)
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H3CCH3,H2CCH2,HCCH
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Electron v molecular geometry
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The molecular geometry of a molecule describes the three-dimensional shape of just the atoms. This is in contrast to the electron geometry, which describes the shape of all electron clouds. The number of electron clouds determines the electron geometry.
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Determine the molecular geometry of CH4. (4, #15)
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tetrahedral
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What is the molecular geometry of a molecule with 3 outer atoms and 1 lone pair on the central atom?
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trigonal pyramidal
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What is the molecular geometry of a molecule with 4 outer atoms and 2 lone pairs on the central atom?
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square planar
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What is the molecular geometry of a molecule with 5 outer atoms and 1 lone pair on the central atom?
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square pyramidal
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Which of the following describes a scenario in which the molecular geometry would have the smallest bond angle(s)?
answer
two bonding domains (or bonding pairs) and two nonbonding domains (or lone pairs)