Download Atom Components and Chemical Symbols Z A

HW Chapter 02
Due: 11:59pm on Sunday, February 19, 2017
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Atom Components and Chemical Symbols
Learning Goal:
To understand the composition of the atom.
Atoms are composed of electrons, neutrons, and protons. Their properties are shown in the table to the right.
Electrons are the lightest of these three subatomic particles. Electrons have a mass of 9.109 × 10 −28 g, which is about 0.05% that of the masses of protons
and neutrons, and are assigned a −1 charge. Electrons are distributed outside the nucleus of an atom. Note that, despite the popular model, electrons do not
orbit at fixed distances from the center of an atom. Rather, they reside within an electron cloud as shown in the figure. Except for nuclear chemistry, all
chemistry involves the distribution of electrons among different atoms of compounds.
Protons have a mass of 1.673 × 10 −24
g
. Protons are assigned a +1 charge.
The third subatomic particle is the neutron. Neutrons have approximately the same mass as protons, but they do
not have a charge. Along with protons, neutrons comprise the nucleus at the center of an atom.
Particle
Mass ( g )
electron
9.109 × 10
proton
1.673 × 10
neutron
1.675 × 10
Atomic mass
units
−28
−24
−24
Electrical charge
(C)
0.0005486
−1.602 × 10
1.007276
+1.602 × 10
1.008665
0
Relative
charge
−19
− 1
−19
+1
0
The atomic number Z is the number of protons in the nucleus of an atom of an element. Each element has a unique number of protons. For example, an atom
with 47 protons is always a silver atom and has an atomic number of 47. The atomic number is used to distinguish different elements from one another.
The mass number A is the sum of the number of protons and neutrons in the nucleus of an atom of an element. Atoms that have the same atomic number
but different mass numbers are called isotopes. For example, all atoms with atomic number 6 are carbon atoms, but carbon atoms with mass numbers of 12
and 13 are isotopes of one another.
Each element is assigned a unique chemical symbol. For example, the symbol for hydrogen is H, and the symbol for oxygen is O. Some elements have
symbols based on their names in languages other than English. For example, the symbol for iron is Fe, which is based on the Latin ferrum.
The atomic number, mass number, and chemical symbol are often combined to describe a given atom. For example, an atom of lithium (Li) with atomic
number 3 and a mass number of 7 could be written 73 Li. Since the atomic number and the symbol are both unique to a given element, the atomic number is
often left off of this notation, leaving 7 Li.
Part A
Which subatomic particle(s) are found in the nucleus of the atom?
Enter the subatomic particle or particles separated by commas.
ANSWER:
Part B
The atomic number of nitrogen is 7. What is the mass number of a nitrogen atom with 6 neutrons?
Express your answer as an integer.
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ANSWER:
mass number = Part C
An atom has a mass number of 27 and 14 neutrons. What is the atomic number of this atom?
Express your answer as an integer.
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ANSWER:
atomic number = Part D
An atom of chlorine is represented by 37
Cl. How many neutrons are in the nucleus of this atom?
17
Express your answer as an integer.
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ANSWER:
neutrons in 37
Cl = 17
Part E
Give the nuclear symbol for the isotope of phosphorus for which A
Enter the nuclear symbol for the isotope (e.g., 42 He).
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ANSWER:
Animation—Rutherford’s Experiment: Nuclear Atoms
Watch the animation and study Rutherford’s nuclear atom model.
Part A ­ Conclusions from Rutherford’s experiment
?
= 31
Watch the animation depicting Rutherford’s experiment and choose which of the following conclusions are correct.
Check all that apply.
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ANSWER:
A positive charge is spread equally over the atom.
The atom is a very compact entity without any empty space.
The majority of the space inside the atom is empty space.
The mass of an atom is concentrated at the nucleus.
The atom contains a positively charged nucleus.
Positive charge is condensed in one location within the atom.
Part B ­ The structure of the atom
On the basis of Rutherford’s experimental observations, which of the following statements describes the structure of the atom according to Rutherford's
atomic model?
Check all that apply.
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ANSWER:
In an atom, the positive charges are located in a small core within the atom called the nucleus.
In an atom, all of the positive and negative charges are randomly distributed.
In an atom, negatively charged electrons are dispersed in the space surrounding the positively charged nucleus of an atom.
In an atom, positively charged particles are dispersed in the space surrounding the negatively charged sphere.
Animation—The Millikan Oil Drop Experiment
Watch the animation to study the Millikan oil drop experiment.
The Millikan oil drop experiment was a direct and convincing experiment for the measurement of the charge on a single electron. Millikan performed an
experiment on a charged oil droplet. By balancing the forces acting on the oil droplet, the charge on a single electron can be calculated. Millikan found that the
charge of an oil droplet is always a whole­number multiple of −1.60 × 10 −19 C. Thus, the charge on a single electron is −1.60 × 10 −19 C.
Various types of forces that are observed in nature
You can observe the following types of forces in nature:
1. The attraction or repulsion between objects or particles that have electrical charge is known as the electric force.
2. The force with which the Earth, the Moon, or any other massively large object attracts another object toward itself is known as the gravitational
force.
3. The force exerted upon an object that is in contact with another stationary object is known as a normal force.
4. The special type of frictional force that acts upon objects as they travel through the air is known as an air resistive force.
5. The force exerted by a compressed or stretched spring upon any object that is attached to it is known as a spring force.
6. The upward force caused by the air pressure that keeps things afloat is known as a buoyant force.
Part A ­ The forces acting on an oil droplet
Watch the animation. Identify the types of forces acting on an oil droplet while the voltage is turned on and the droplet is either falling or rising.
Check all that apply.
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ANSWER:
Buoyant force
Spring force
Electric force
Gravitational force
Normal force
Air resistive force
Part B ­ The effect of an electric field (voltage) on a negatively charged oil droplet
In the Millikan oil droplet experiment, the oil is sprayed from an atomizer into a chamber. The droplets are allowed to pass through the hole into the
chamber so that their fall can be observed. The top and bottom of the chamber consist of electrically charged plates. The upper plate is positively
charged, and the lower plate is negatively charged. X rays are introduced into the chamber so that when they strike the oil droplets, the droplets will
acquire one or more negative charges. The electric field (voltage) is applied to the metal plates.
Watch the animation and identify the effects of an electric field on the motion of a negatively charged oil droplet. Consider the gravitational force as Fg
and the electric force as Fe . All the other forces acting on the oil droplet can be ignored as their effect on the motion of the oil droplet is negligible.
Check all that apply.
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ANSWER:
If Fe is increased until it is equal to Fg , the negatively charged oil droplet will remain stationary.
If Fe is greater than Fg , the negatively charged oil droplet will move freely toward the negatively charged plate.
In the absence of an electric field, the oil droplet falls freely due to the gravitational force.
In the presence of an electric field, the negatively charged oil droplet moves freely toward the negatively charged plate.
Part C ­ The total charge on a negatively charged oil droplet
In Millikan’s experiment, the oil droplets acquire one or more negative charges by combining with the negative charges that are produced from the
ionization of air by X rays. By measuring the charges on the oil droplets, he calculated the charge on a single electron as −1.60 × 10 −19 C. The charge
on any negatively charged oil droplet is always a whole­number multiple of the fundamental charge of a single electron.
If Millikan was measuring the charge on an oil droplet with 7 negatively charged electrons on it, what charge would he have measured on the droplet?
Express your answer to three significant figures and include the appropriate units.
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ANSWER:
The Periodic Table
Learning Goal:
To understand the arrangement of the periodic table and identify certain groups of elements by name (e.g. halogens, metals, lanthanides etc.).
The periodic table is a list of elements arranged by atomic number. As you can see in the image below, the atomic number for each
element is the whole number in the cell. The atomic mass, written below the symbol here although it may appear elsewhere in
some periodic tables, is the average mass of the isotopes of that element.
Groups and periods
Columns in the periodic table are called groups, and the rows are called periods. Notice that the groups are labeled 1 to 18 and the periods are labeled 1 to 7.
Groups 1, 2, and 13 to 18 are called the main group elements, groups 3 to 12 are the transition elements, and the bottom two rows are called the lanthanides
and actinides, respectively.
This table gives properties and alternate names for some of the groups:
Group
Name
Properties
1
Alkali metals
React to form 1+ ions.
2
Alkaline earths
React to form 2+ ions.
17
Halogens
React to form 1− ions.
18
Rare gases
(noble gases)
Stable and unreactive. (Elements from other groups
form ions to achieve the same number of electrons as
a noble gas.)
Metals vs. nonmetals
Notice the heavy zigzag line running diagonally across the right part of the table. This line separates metals (below and to the left of the line) from the
nonmetals (above and to the right of the line). Metals tend to lose electrons to form positive ions, whereas nonmetals tend to gain electrons to form negative
ions.
Part A
What is the atomic number of the element located in group 16, period 2 of the periodic table?
Enter the atomic number.
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ANSWER:
Part B
If a new element were discovered and it was found to form 1− ions, in which group would you place it in the periodic table?
Enter the group number.
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ANSWER:
Part C
Which of the following elements is not a metal?
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ANSWER:
iron
aluminum
sodium
phosphorus
Part D
Which of the following is not an element?
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ANSWER:
water
lithium
sulfur
lead
± Avogadro's Number
Learning Goal:
To use Avogadro's number to convert between microscopic units of atoms and molecules to the macroscopic world of chemical experiments.
A mole is a unit of matter that represents a known number of particles that is large enough to be weighed on a laboratory balance. One mole of substance
contains 6.022 × 10 23 formula units, as shown in the following unit factor:
23
6.022×10
f ormula units
1 mol substance
The value 6.022 × 10 is called Avogadro's number. The term formula unit is a generic phrase that can mean a molecule, atom, ion, or whatever is
represented by the chemical formula. For example, a mole of He contains 6.022 × 10 23 helium atoms. A mole of N2 contains 6.022 × 10 23 diatomic N2
molecules but double that number of nitrogen atoms.
23
Part A
A flask contains 0.190 mol of liquid bromine, Br2 . Determine the number of bromine molecules present in the flask.
Express your answer numerically in molecules.
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ANSWER:
molecules 6
9
12
24
You may know that a million is 10 , a billion is 10 , and a trillion is 10 . A trillion trillion would be 10 which is also known as a septillion.
Part B
Calculate the mass of 1.00 × 10 24 (a septillion) molecules of water.
Express the answer numerically in grams.
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ANSWER:
g Part C
The fuel used in many disposable lighters is liquid butane, C4 H10 . How many carbon atoms are in 1.00 g of butane?
Express your answer numerically in atoms.
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ANSWER:
carbon
atoms
Calculations Using the Mole
Learning Goal:
To learn how to convert grams to moles and to use the mole to find the number of atoms in a sample.
The mole (abbreviated mol) is a counting unit used to simplify calculations that would otherwise involve very large numbers. The mole is equivalent to the
number of carbon atoms in exactly 12 g of isotopically pure 12 C, or 6.02 × 10 23 . This number is known as Avogadro's number in honor of Amedeo Avogadro.
Avogadro's number can be used as a conversion factor between moles and atoms as shown here:
23
6.02×10
atoms
1 mole of atoms
The molar mass of a substance is the mass of one mole of a substance and is written in units of grams per mole. The molar mass of an atom is equivalent to
its atomic mass whereas the molar mass of a substance is equivalent to its formula weight.
Part A
How many moles of atoms are in 8.00 g of 13 C?
Express your answer numerically in moles.
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ANSWER:
mol 13 C Part B
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Part C
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Part D
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The Law of Multiple Proportions
Consider two different compounds of carbon and oxygen: carbon dioxide, CO2 , and carbon monoxide, CO. The number of oxygen atoms per carbon atom in CO2 is double the number of oxygen atoms per carbon atom in CO. So we can predict that the mass of oxygen per gram of carbon in CO2 is double the
mass of oxygen per gram of carbon in CO. And, in fact, if other carbon­oxygen compounds existed, we could predict small, whole­number ratios for the
masses of oxygen per gram of carbon in all of them.
This is exactly what John Dalton predicted for compounds using his atomic theory of matter. It came to be known as the law of multiple proportions.
Part A
There are two different compounds of sulfur and fluorine.
In SF6 , the mass of fluorine per gram of sulfur is 3.55 g F/g S.
In the other compound, SFX , the mass of fluorine per gram of sulfur is 1.18 g F/g S.
What is the value of X for the second compound?
Express your answer as an integer.
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ANSWER:
X =
Before the mole
The law of multiple proportions predates the concept of a mole or molar mass. Thus, scientists like John Dalton could only determine the relative amounts of
each type of atom in a formula, and not the exact formula. For example, Dalton could determine that there were two carbon­oxygen compounds, one with twice
as much oxygen as the other. However, he did not know for sure that the formulas were CO and CO2 . Other possibilities (given what they knew at the time)
could have been C2 O and C2 O2 , or CO2 and CO4 , etc.
Part B
Samples of three different compounds were analyzed and the masses of each element were determined.
Compound
Mass N Mass O
(g)
(g)
A
5.6
3.2
B
3.5
8.0
C
1.4
4.0
If you were John Dalton and had never heard of a mole, which of the following would you think were possible sets of formulas for the compounds A, B,
and C, respectively?
Check all that apply.
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ANSWER:
NO
, NO2 , NO4 , N 2 O N 2 O4
, N2 O5 NO4
, NO10 , NO5 NO2
, NO8 , NO10 ± Monel Metal
Monel metal is a corrosion­resistant copper­nickel alloy used in the electronics industry. A particular alloy with a density of 8.80 g/cm3 and containing 0.031 % Si by mass is used to make a rectangular plate that is 15.0 cm long, 12.5 cm wide, and 2.50 mm thick and has a 2.50­cm­diameter hole drilled through
its center such that the height of the hole is 2.50 mm .
The silicon in the plate is a mixture of naturally occurring isotopes. One of the those isotopes is silicon­30, which has an atomic mass of 29.97376 amu. The
percent natural abundance, which refers to the atoms of a specific isotope, of silicon­30 is 3.10%.
Part A
What is the volume of the plate?
Express the volume numerically in cubic centimeters.
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ANSWER:
cm3 Part B
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Applying Dalton's Atomic Theory
As early as 400 B.C., Greek philosophers proposed that matter was made up of particles. During the 1800s, John Dalton linked the idea of atoms with the
chemical identity of an element. His atomic theory of matter involved the following postulates.
1. Each element is composed of extremely small particles called atoms.
2. All atoms of a given element are identical to one another in mass and other properties, but the atoms of one element are different from the atoms
of other elements.
3. Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in
chemical reactions.
4. Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of
atoms.
Scientists later discovered isotopes, which showed that the second postulate was not entirely true, and nuclear reactions, which showed that the third
postulate was not true.
Part A
Which of the following reactions is possible according to Dalton's atomic theory?
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ANSWER:
N 2 →O2
N 2 + O2 →2NO
CO2 →NO2
H 2 O→H 2 S
Part B
The law of conservation of mass states that mass is neither created nor destroyed during a chemical reaction. This can be gleaned from the third
postulate in Dalton's series.
Magnesium oxide decomposes into magnesium and oxygen. If 16.12 g of magnesium oxide decomposes to form 9.72 g of magnesium, what mass of
oxygen gas is also released in the reaction?
Express your answer with the appropriate units.
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ANSWER:
Ions and the Periodic Table
A main group metal tends to lose electrons, forming a cation with the same number of electrons as the nearest noble gas in the periodic table. A main group
nonmetal tends to gain electrons, forming an anion with the same number of electrons as the nearest noble gas. The various groups gain or lose electrons as
summarized in the following table:
Group
Tendency
Charge
1A
Lose one electron
+1
2A
Lose two electrons
+2
3A
Lose three electrons
+3
5A
Gain three electrons
–3
6A
Gain two electrons
–2
7A
Gain one electron
–1
8A
Rarely gain or lose electrons
0
Part A
If the following elements were to form ions, they would attain the same number of electrons as which noble gas?
Drag the appropriate elements to their respective bins.
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ANSWER:
Reset
Br
He
Li
O
Cl
Ne
K
Na
Ar
Help
Rb
Kr
Part B
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Part C
A certain element forms an ion with 54 electrons and a charge of +2. Identify the element.
Express your answer as a chemical symbol.
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ANSWER:
Subatomic Particles
Learning Goal:
To determine the number of protons, neutrons, and electrons in a given isotope or ion.
Atoms are composed of three fundamental particles. Protons are positively charged, neutrons are neutral, and electrons are negatively charged. Protons and
neutrons are clustered into a dense core called the nucleus, whereas electrons are found outside of the nucleus at a relatively large distance. Elements differ
from one another by how many protons their atoms they contain. The number of protons is called the atomic number (Z) of the element. Since protons and
neutrons make up most of the mass of an atom, the sum of the protons and neutrons is its mass number (A). In neutral atoms, the numbers of protons and
electrons are equal. In ions, the numbers of electrons and protons are not equal.
Part A
Specify the number of protons, neutrons, and electrons in the neutral atom bromine­80.
Enter your answers as integers separated by commas.
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ANSWER:
protons, neutrons, electrons
Part B
The ion N3− has _____ protons and _____ electrons.
Enter your answers as integers separated by a comma.
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ANSWER:
Part C
What isotope has 13 protons and 14 neutrons?
Enter the name of the element followed by a hyphen and the mass number (e.g., uranium‐234).
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ANSWER:
Part D
Which element does X represent in the following expression: 55
X?
25
Enter the chemical symbol of the element.
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ANSWER:
± Isotopes and Atomic Mass
Most elements occur naturally as a mix of different isotopes. An element's atomic mass is the weighted average of the isotope masses. In other words, it is
an average that takes into account the percentage of each isotope. For example, the two naturally occurring isotopes of boron are given here.
Isotope
10
11
Isotopic mass Relative abundance
(amu)
(%)
B
10.0
19.9
B
11.0
80.1
The atomic mass of boron is calculated as follows:
(10.0 × 0.199) + (11.0 × 0.801) = 10.8 amu
Because the heavier isotope is more abundant, the atomic mass is closer to 11 amu than it is to 10 amu.
Part A
What is the atomic mass of a hypothetical element that consists of the following isotopes in the indicated natural abundances?
Isotope
Isotopic mass Relative abundance
(amu)
(%)
1
81.9
14.5
2
85.9
12.9
3
87.9
72.6
Express your answer to three significant figures and include the appropriate units.
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ANSWER:
Part B
What is the atomic mass of the element that consists of the following isotopes in the indicated natural abundances?
Isotope
Isotopic mass
(amu)
Relative abundance (%)
1
57.93
67.76
2
59.93
26.16
3
60.93
1.25
4
61.93
3.66
5
63.93
1.16
Express your answer to three significant figures and include the appropriate units.
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ANSWER:
± Neutrons and Isotopes
Periodic table
The periodic table lists two main numbers for each element. The atomic number is an integer that equals the number of protons. The number of neutrons is not
given in the periodic table because it will vary with different isotopes. The mass number of an element is the sum of the protons and neutrons. To find the
number of neutrons, the atomic number must be subtracted from the mass number.
Elemental symbol
When writing the symbol for an element, a superscript indicates the mass number and a subscript indicates the atomic number. For example, 14
C has a mass
6
number of 14 and an atomic number of 6. This isotope can also be written as just 14 C. You do not need to put in the 6 because the atomic number of carbon
is always 6 regardless of which isotope you are dealing with.
Part A
How many neutrons are found in one atom of 16 N?
Express your answer numerically.
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ANSWER:
Atomic mass
Since the number of neutrons varies in the periodic table, neither then number of neutrons nor the mass number (number of neutrons plus protons) is shown.
What we do see is the atomic mass, or a weighted average of all the isotope masses. This is the noninteger listed with an element; it is the number with
several decimal places. An element's atomic mass is the weighted average of the isotope masses. In other words, it is an average that takes into account the
percentage of each isotope. To find the weighted average, multiply each isotopic mass by its relative abundance and find the sum for each isotope of an
element.
Part B
A certain element X has four isotopes.
0.5600% of X has a mass of 83.91343 amu.
9.860% of X has a mass of 85.90927 amu.
7.000% of X has a mass of 86.90890 amu.
82.58% of X has a mass of 87.90562 amu.
What is the average atomic mass of element X?
Express your answer numerically to four significant figures.
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ANSWER:
amu Part C
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Part D
37
The two isotopes of chlorine are 35
Cl and Cl. Which isotope is the most abundant?
17
17
You did not open hints for this part.
ANSWER:
35
17
37
17
Cl
Cl
The Periodic Table: Groups, Periods, and Classes
The periodic table is the most important organizing principle in chemistry. There is a regular progression in the periodic table that reflects a similar regularity in
the structures and properties of the different elements. If you know the properties of any one element in a group, you can make a good guess at the properties
of every other element in the same group and even the elements in neighboring groups. Familiarizing yourself with the structure and arrangement of the
periodic table early on will help you later on in chemistry.
Part A
Classify the following elements as main group elements, transition metals, or inner transition metals.
Drag the appropriate elements to their respective bins.
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ANSWER:
Reset
Th
Main group elements
Ag
N
Ba
Zn
Pb
Transition metals
Part B
Classify the following elements as halogens, alkali metals, alkaline earth metals, or noble gases.
Drag the appropriate elements to their respective bins.
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ANSWER:
Inner transition metals
Help
Cl
Halogens
Xe
Ba
I
Alkali metals
K
Reset
Help
Reset
Help
Rb
Alkaline earth metals
Noble gases
Part C
Match each element to its period.
Drag the appropriate elements to their respective bins.
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ANSWER:
Ir
Period 1
Period 2
Period 3
Ra
H
Cr
Period 4
Part D
Classify the following elements as metal, nonmetal, or metalloid (semimetal).
S
C
In
Period 5
Period 6
Period 7
Drag the appropriate elements to their respective bins.
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ANSWER:
Reset
Rb
Metal
Ne
Si
Nonmetal
S
Sb
Help
Zr
Metalloid
Exercise 2.4
A 1.446 − g sample of potassium reacts with 8.182 g of chlorine to produce potassium chloride as the only product. After the reaction, 6.871 g of chlorine
remains unreacted.
Part A
What mass of potassium chloride was formed?
Express your answer using four significant figures.
ANSWER:
m
= g Exercise 2.12
In one experiment, the reaction of 1.00 g mercury and an excess of sulfur yielded 1.16 g of a sulfide of mercury as the sole product. In a second experiment,
the same sulfide was produced in the reaction of 1.48 g mercury and 1.10 g sulfur.
Part A
What mass of the sulfide of mercury was produced in the second experiment?
ANSWER:
m
= 1.72 g Correct
Part B
Which element (mercury or sulfur) remained unreacted in the second experiment?
ANSWER:
mercury
sulfur
Correct
Part C
What mass remained unreacted in the second experiment?
Express your answer using two significant figures.
ANSWER:
m
= 0.86 g Correct
Exercise 2.28
For the ion 228 Ra2+ with a mass of 228.030 u, determine
Part A
the number of protons in the ion
ANSWER:
protons Part B
the number of neutrons in the ion
ANSWER:
neutrons Part C
the number of electrons in the ion
ANSWER:
electrons Part D
the ratio of the mass of this ion to that of an atom of 16 O (the mass of 16 O is 15.9949 u)
Express your answer using six significant figures.
ANSWER:
ratio
= Exercise 2.29
An isotope of silver has a mass that is 6.68374 times that of oxygen­16. 16 O has a mass of 15.994915 u.
Part A
What is the mass in u of this isotope?
Express your answer to six significant figures and include the appropriate units.
ANSWER:
isotopic mass = Exercise 2.30
The ratio of the masses of the two naturally occurring isotopes of indium is 1.0177:1. The heavier of the two isotopes has 7.1838 times the mass of 16 O (the
mass of 16 O is 15.9949 u).
Part A
What is the mass in u of the heavier isotope?
Express your answer using six significant figures.
ANSWER:
m
= u Part B
What is the mass in u of the lighter isotope?
Express your answer using six significant figures.
ANSWER:
m
= u Exercise 2.31
The following data on isotopic masses are from a chemical handbook. What is the ratio of each of these masses to that of 126 C.
Part A
58
26
, 57.93328 u ;
Fe
Express your answer using seven significant figures.
ANSWER:
ratio
= Part B
47
22
Ti
, 46.95176 u ;
Express your answer using seven significant figures.
ANSWER:
ratio
= Part C
235
92
U
, 235.0439 u .
Express your answer using seven significant figures.
ANSWER:
ratio
= Exercise 2.32 ­ Enhanced ­ with Feedback
The following ratios of masses were obtained with a mass spectrometer: 199 F/
35
17
81
35
19
Cl/
9
35
Br/
17
12
6
.
Cl = 2.3140
You may want to reference (
page ) Section 2.1 while completing this problem.
Part A
Determine the mass of a 81
Br atom in amu.
35
Express your answer using five significant figures.
ANSWER:
mass of 81
Br = 35
amu Exercise 2.33
Part A
Which of the following species has equal numbers of neutrons and electrons?
ANSWER:
24
47
60
35
Mg
3+
−
Cl
124
226
90
2+
Cr
Co
Sn
2+
Th
Sr
Part B
Which of the following species has protons, neutrons, and electrons in the ratio 9:11:8?
ANSWER:
C = 1.5832;
F = 1.8406;
24
47
60
35
Mg
Cr
Co
3+
−
Cl
124
226
90
2+
Sn
2+
Th
Sr
Part C
Which of the following species has a number of neutrons equal to the number of protons plus one­half the number of electrons? ANSWER:
24
47
60
35
Mg
Cr
Co
3+
−
Cl
124
226
90
2+
Sn
2+
Th
Sr
Exercise 2.44
There are four naturally occurring isotopes of chromium. Their masses and percent natural abundances are 49.9461 u, 4.35%; 51.9405 u, 83.79%; 52.9407 u,
9.50%; and 53.9389 u, 2.36%.
Part A
Calculate the weighted­average atomic mass of chromium.
Express your answer using four significant figures.
ANSWER:
= atomic mass
u Exercise 2.45
The two naturally occurring isotopes of lithium have the following abundances: 6 Li, 7.590 % ; 7 Li, 92.41 % . The mass of 6 Li is 6.0151228 u .
Part A
What is the mass of 7 Li?
Express your answer using four significant figures.
ANSWER:
mass of 7 Li = u Exercise 2.46
Bromine has two naturally occurring isotopes. One of them, bromine­79, has a mass of 78.918336 u and a natural abundance of 50.69 % .
Part A
What must be percent natural abundance of the other isotope, bromine­81?
Express your answer using four significant figures.
ANSWER:
= % % second isotope
Part B
What must be the mass of the other isotope, bromine­81?
Express your answer to four significant figures and include the appropriate units.
ANSWER:
m
= Exercise 2.47
The three naturally occurring isotopes of neon are 20 Ne, 19.992440 u ; 21 Ne, 20.993847 u ; and 22 Ne. The percent natural abundances of 20 Ne and 22 Ne are 90.4800 % and 9.2500 % , respectively.
Part A
Determine the isotopic mass of 22 Ne.
Express your answer to five significant figures and include the appropriate units.
ANSWER:
m
= Exercise 2.58
Part A
Determine the number of Kr atoms in a 5.55 − mg sample of krypton.
ANSWER:
N
= atoms Part B
Determine the molar mass, M , of an element if the mass of a 2.80
× 10
sample of the element is 2.09 g.
22
− atom
ANSWER:
M
= g/mol Part C
Determine the identity of an element if the mass of a 2.80
× 10
22
sample of the element is 2.09 g.
− atom
ANSWER:
Potassium
Calcium
Titanium
Scandium
Part D
Determine the mass of a sample of phosphorus that contains the same number of atoms as 44.80 g of magnesium.
Express your answer using four significant figures.
ANSWER:
m
= g Exercise 2.60
Part A
How many atoms are present in a 70.0 − cm3 sample of plumber's solder, a lead–tin alloy containing 67% Pb by mass and having a density of 9.4 3
g/cm ?
Express your answer using two significant figures.
ANSWER:
N
= atoms Exercise 2.62
A particular lead–cadmium alloy is 8.0% cadmium by mass.
Part A
What mass of this alloy, in grams, must you weigh out to obtain a sample containing 6.70×1023 Cd atoms?
Express your answer using two significant figures.
ANSWER:
m
= g Exercise 2.65
Without doing detailed calculations, determine which of the following samples has the greatest number of atoms.
Part A
a cube of iron with a length of 10.0 cm (d = 7.86 g/cm3 )
16.0 kg of oxygen contained in a 10,000 L balloon
a mound of silicon weighing 16.0 kg
a 76 lb sample of liquid mercury (d = 13.5 g/mL)
ANSWER:
Si
O2
Hg
Fe
Exercise 2.67
In each case, identify the element in question.
Part A
The mass number of an atom is 234 and the atom has 60.0% more neutrons than protons.
ANSWER:
234
234
234
234
U
Th
Pa
Ac
Part B
An ion with a 2 + charge has 10.0% more protons than electrons.
ANSWER:
Sc
2+
2+
Ca
V
2+
Ti
2+
Part C
An ion with a mass number of 110 and a 2 + charge has 25.0% more neutrons than electrons.
ANSWER:
110
110
110
110
Cd
2+
2+
In
2+
Sb
2+
Sn
Exercise 2.66
Without doing detailed calculations, determine which of the following samples occupies the largest volume.
Part A
25.5 mol of sodium metal (d = 0.971 g/cm3 )
0.725 L of liquid bromine (d = 3.12 g/mL)
0.725 L of liquid bromine (d = 3.12 g/mL)
25
atoms of chromium metal (d = 9.4g/cm3 )
2.15 kg of plumber's solder (d = 9.4 g/cm3 ) a lead­tin alloy with a 2:1 atom ratio of lead to tin
1.25 ⋅ 10
ANSWER:
bromine
sodium
chromium
a lead­tin alloy
Score Summary:
Your score on this assignment is 1.6%.
You received 4 out of a possible total of 249 points.