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Homework 7 Chapter 07
Homework 7 Chapter 07
Due: 11:59pm on Wednesday, November 2, 2016
You will receive no credit for items you complete after the assignment is due. Grading Policy
Problem 7.17
Part A
Which will experience the greater effective nuclear charge, the electrons in the n
shell in Ar or the n
= 3
shell in Kr?
= 3
ANSWER:
electrons in the n
= 3
shell in Ar
electrons in the n
= 3
shell in Kr
Correct
Part B
Which will be closer to the nucleus?
ANSWER:
electrons in the n
= 3
shell in Ar
electrons in the n
= 3
shell in Kr
Correct
Ionic Radii
The size of ions as measured by ionic radii varies in a systematic manner. The size of the ion can be explained in part by effective nuclear charge, Zef f , which is
the net nuclear charge felt by an electron. The effective nuclear charge takes into account the actual nuclear charge and the shielding of this charge by inner
electrons. When an atom loses electrons, the resulting cation is smaller both because the remaining electrons experience a larger Zef f and because these
electrons are usually in orbitals closer to the nucleus than the electrons that were lost. The more electrons that are lost, the smaller the ion becomes.
Similarly, when an atom gains electrons, the resulting anion is larger owing to both increased electron­electron repulsions and a reduction in Zef f . The more
electrons that are gained, the larger the ion becomes.
Part A
Rank the following ions in order of decreasing radius: Be2+ ,Mg2+ ,Ca2+ ,Sr2+ , and Ba2+ . Use the periodic table as necessary.
Rank from largest to smallest radius. To rank items as equivalent, overlap them.
Hint 1. How to approach the problem
First locate each of the elements on the periodic table. Then, keeping in mind that ionic radii increase for ions with the same charge going down a row,
sort the ions in order of increasing radii.
ANSWER:
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Largest radius
Smallest radius
The correct ranking cannot be determined.
Correct
Part B
Rank the following items in order of decreasing radius: Mg, Mg2+ , and Mg2− .
Rank from largest to smallest radius. To rank items as equivalent, overlap them.
Hint 1. Specify the smallest species
As electrons are removed from an atom, the remaining electrons are pulled closer to the positively charged nucleus. Conversely, if electrons are
added to an atom, the nucleus becomes less efficient in attracting a larger number of electrons. For a given atom, which species would likely have the
smallest radius?
ANSWER:
the anion
the neutral atom
the cation
ANSWER:
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Largest radius
Smallest radius
The correct ranking cannot be determined.
Correct
Part C
The following ions contain the same number of electrons. Rank them in order of decreasing ionic radii.
Rank from largest to smallest radius. To rank items as equivalent, overlap them.
Hint 1. Identify the effect of ionic charge on cationic radius
These ions (K+ ,Sc3+ , and Ca2+ ) all contain the same number of electrons in the same principal quantum level but differ in the number of protons.
For this series, as more electrons are removed, what happens to Zef f ?
ANSWER:
Zef f increases and the ionic radius becomes larger.
Zef f decreases and the ionic radius becomes larger.
Zef f increases and the ionic radius becomes smaller.
Zef f decreases and the ionic radius becomes smaller.
Hint 2. Compare the radius of the cations
Arrange the cations shown from largest to smallest radius.
Rank from largest to smallest radius. To rank items as equivalent, overlap them.
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Largest radius
Smallest radius
The correct ranking cannot be determined.
Hint 3. Identify the effect of ionic charge on anionic radius
These ions (Cl− ,S2− , and P3− ) all contain the same number of electrons in the same principal quantum level but differ in the number of protons. For
this series, as more electrons are added, what happens to Zef f ?
ANSWER:
Zef f decreases and the ionic radius becomes larger.
Zef f decreases and the ionic radius becomes smaller.
Zef f increases and the ionic radius becomes smaller.
Zef f increases and the ionic radius becomes larger.
Hint 4. Compare the radius of the anions
Arrange the anions shown from largest to smallest radius.
Rank from largest to smallest radius. To rank items as equivalent, overlap them.
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Largest radius
Smallest radius
The correct ranking cannot be determined.
Hint 5. Compare the radius of the anions and cations
For ions with the same number of electrons, which will have a larger radius, the anions or the cations?
Hint 1. Relationship between effective nuclear charge and size
Because the ions contain the same number of electrons in the same principal quantum level, the number of protons in the nucleus will
determine the relative magnitude of Zef f . As Zef f increases, the radius will decrease. For example, K+ has 19 protons and Cl− has 17
protons. The electrons of K+ are attracted by more protons and experience a larger Zef f . The opposite effect will occur for Cl− . How does this
affect the radii of the two ions?
ANSWER:
larger
The anions are smaller
than the cations.
ANSWER:
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Largest radius
Smallest radius
The correct ranking cannot be determined.
Correct
In a group of ions with the same number of electrons, the most negative ion is the largest and the most positive ion is the smallest.
Sample Exercise 7.2 Practice Exercise 1 with feedback
Part A ­ Predicting Relative Sizes of Atomic Radii
By referring to a periodic table , but not to Figure 7.7, place the following atoms in order of increasing bonding atomic radius: N, O, P, Ge.
ANSWER:
O < N < P < Ge
N < P < Ge < O
N < O < P < Ge
O < N < Ge < P
P < N < O < Ge
Correct
As your go down a group and across a period from group 1 to group 8, the bonding atomic radius increases. O increasing bonding atomic radius.
are in order of
< N < P < Ge
Electron Configurations of Atoms and Ions
The electron configuration of an atom tells us how many electrons are in each orbital. For example, helium has two electrons in the 1s orbital. Therefore the
electron configuration of He is 1s2 .
Part A
What is the ground­state electron configuration of a neutral atom of nickel?
Express your answer in condensed form, in order of increasing orbital energy. For example, [He]2s2 2p2 would be entered as [He]2s^22p^2 .
Hint 1. Determine the number of electrons
How many electrons are there in a neutral atom of nickel?
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Express your answer as an integer.
ANSWER:
28
Hint 2. Determine nickel’s block
Look at a periodic table. In which block is nickel found?
ANSWER:
s
p
d
f
Hint 3. Identify the preceding noble gas
Which is the noble gas that is placed in the previous row for nickel?
ANSWER:
Xe
Kr
Ne Ar
ANSWER:
1s^22s^22p^63s^23p^64s^23d^8
Correct
Part B
What is the ground­state electron configuration of the oxide ion O2− ?
Express your answer in condensed form, in order of increasing orbital energy. For example, [He]2s2 2p2 should be entered as [He]2s^22p^2 .
Hint 1. Determine the number of electrons
Using the fact that the number of electrons in the O2− ion is equal to the number of electrons present in the neutral oxygen atom plus the charge on
the O2− ion, determine how many electrons are in this ion.
Express your answer as an integer.
ANSWER:
10
ANSWER:
1s^22s^22p^6 Correct
Part C
Which element has the following configuration: [Xe]6s2 4f 11 ?
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Homework 7 Chapter 07
Enter the chemical symbol for the element.
Hint 1. Count electrons
Neutral xenon has 54 electrons. This element has a xenon configuration plus an additional two electrons in the 6s subshell and eleven electrons in the
4f subshell.
How many electrons are in an atom of this element?
Express your answer as an integer.
ANSWER:
67.0
ANSWER:
Ho
Correct
Sample Exercise 7.6 Practice Exercise 1 with feedback
Part A ­ Periodic Trends in Ionization Energy
Consider the following statements about first ionization energies:
I. Because the effective nuclear charge for Mg is greater than that for Be, the first ionization energy of Mg is greater than that of Be.
II. The first ionization energy of O is less than that of N because in O we must pair electrons in the 2p orbitals.
III. The first ionization energy of Ar is less than that of Ne because a 3p electron in Ar is farther from the nucleus than a 2p electron in Ne.
Which of the statements I, II, and III is or are true?
ANSWER:
Only one of the statements is true
Statements I and II are true
Statements I and III are true
Statements II and III are true
All three statements are true
Correct
With regards first ionization energy, the following two statements hold true:
The first ionization energy of O is less than that of N because in O we must pair electrons in the 2p orbitals.
The first ionization energy of Ar is less than that of Ne because a 3p electron in Ar is farther from the nucleus than a 2p electron in Ne.
Sample Exercise 7.5 Practice Exercise 1 with feedback
Part A ­ Trends in Ionization Energy
The third ionization energy of bromine is the energy required for which of the following processes?
ANSWER:
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Br(g) → Br+ (g) + e−
Br+ (g) → Br2+ (g) + e−
Br(g) → Br2+ (g) + 2e−
Br(g) → Br3+ (g) + 3e−
Br2+ (g) → Br3+ (g) + e−
Correct
Problem 7.52 with feedback
You may want to reference (
pages 272 ­ 273) Section 7.5 while completing this problem.
Part A
−
What is the relationship between the ionization energy of an anion with a ­1 charge, such as F , and the electron affinity of the neutral atom, F?
Express your answer in terms of EF , which represents the electron affinity of the neutral atom, F.
ANSWER:
I1F−
= −EF
Correct
−
The ionization energy (removal of an electron) for the formation of F and the electron affinity for the formation of F will be equal in magnitude and
opposite in sign since they describe the same process in opposite directions. The fluoride ion is a stable anion, so the electron affinity of F will have a
−
negative value (indicating a release in energy), whereas the ionization energy of F will be positive.
Group 3 to 12 Elements
The elements from group 3 to group 12 in the periodic table are often called the transition metals. These elements exhibit the characteristic properties of metals
and are often found in more than one oxidation state.
Part A
In the group 3 to group 12 elements, which subshell is filled up going across the rows?
Hint 1. The periodic table as a guide
Recall that the periodic table arranges the elements in the same order as the filling order used in writing electron configurations. The elements fall into
main blocks depending on the type of subshell being filled.
ANSWER:
s subshell
p subshell
d subshell
f subshell
Correct
In the group 3 to group 12 transition metals, the outermost s electron shell contains one or two electrons. However, in these metals, it is the d subshells
that fill up going across the row. In period 4 of the table, the 3d subshell fills, and in periods 5 and 6, the 4d and 5d subshells fill, respectively. It is
important to keep in mind that this filling is not always regular. For example, in period 4, element 23, vanadium, has an electron configuration of 3
5
2
[Ar]3d 4s , but element 24, chromium, has an electron configuration of [Ar]3d 4s.
Part B
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Homework 7 Chapter 07
A sample of soil from a newly discovered cave is analyzed by a team of explorers. They find an element that is a good conductor of electricity. It also forms
a chloride in the form XCl2 and an oxide in the form XO. The element is a liquid at room temperature. What is the identity of this element?
Express your answer using a chemical symbol.
Hint 1. How to approach the problem
Use the information you are given to narrow down the choices that fit the data. First, use the conductivity data to determine whether the element is a
metal, nonmetal, or semimetal. Second, determine the possible oxidation states of the element by examining the oxides and chlorides it can form.
Finally, use the physical data about the element to make a final determination of the element's identity.
Hint 2. Identify the element as a metal, a semimetal, or a nonmetal
Given the conductivity of the element, in which category does the element belong?
ANSWER:
metal
semimetal
nonmetal
Hint 3. Determine the oxidation state of the metal
What is the oxidation state of the element in the compounds it was observed to form?
Express the oxidation state numerically (e.g., +1).
Hint 1. How to determine an oxidation state
The sum of the oxidation states in a neutral compound must add to zero, or
Σ oxidation states = 0
First, find the element in the compound whose oxidation state you know (O is usually −2, and the halogens are usually −1). Then, use this
number and the fact that the compound is neutral to determine the unknown element's oxidation state.
ANSWER:
+2
Hint 4. Identify the liquid elements
Which two elements are liquids at room temperature?
Express your answer as two element symbols separated by commas (e.g., Ca,Mo).
Hint 1. Other characteristics of liquid elements
One of the elements that is a liquid at room temperature is used in barometers and the other is a member of the halogen family (group 17).
ANSWER:
Hg,Br
ANSWER:
Hg
Correct
Sample Exercise 7.10 Practice Exercise 1 with feedback
Part A ­ Reactions of an Alkali Metal
Consider the following three statements about the reactivity of an alkali metal M with oxygen gas:
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I. Based on their positions in the periodic table, the expected product is the ionic oxide M2 O.
II. Some of the alkali metals produce metal peroxides or metal superoxides when the react with oxygen.
III. When dissolved in water, an alkali metal oxide produces a basic solution.
Which of the statements I, II, and III is or are true?
ANSWER:
Only one of the statements is true
Statements I and II are true
Statements I and III are true
Statements II and III are true
All three statements are true
Correct
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