Download Topic 2 Atomic Structure File

Topic 2
Atomic Structure
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Definitions
Learn these off by Heart
Anion: A negatively charged ion.
Atom: The smallest unit of matter
Atomic emission spectra: The characteristic line spectrum that occurs as a result of energy
being released by individual elements. Coloured lines on a black background.
Atomic absorption spectra: The characteristic line spectrum that occurs as a result of
energy being absorbed by individual elements. Black lines on a continuum (coloured)
background.
Atomic number: Number of protons in the nucleus.
Atomic Mass (Mass number): Number of nucleons (protons and neutrons) in the nucleus
Cation: A positively charged ion
Electron: A negatively charged particle. Orbits the nucleus of an atom.
Ion: A charged atom with unequal numbers of protons and electrons.
Isotopes: Atoms that contain the same number of protons but a different number of
neutrons.
Mass Spectrometer: A device that can identify that can separate and detect particles with
different masses.
Neutron: A sub atomic particle within the nucleus of an atom. Has no charge (neutral)
Nucleus: The centre of an atom. Contains protons and neutrons.
Proton: A sub-atomic particle found in the nucleus of an atom. Positively charged.
Relative abundances: The percentage of natural occurrence of an isotope of an element.
Relative atomic mass: The weighted mean of all the naturally occurring isotopes of the
element relative to 12C. No units.
Valence electrons: The electrons in the highest main energy level.
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Topic 2.1 The Atom Worksheet
1. Complete the following table
Name of
element
Symbol
Atomic
Number
(Z)
Al
Mass
Number
Number of
Protons
Number of
Neutrons
Number of
Electrons
27
12
12
Potassium
20
16
15
16
56
26
59
27
59
27
2.
here
are
four
isoto
pes
of
sulf
ur
with
mass
num
bers
32,
33,
34,
and
36.
a. Write the symbol for each of these atoms.
b. How are these isotopes alike?
c. How are they different?
d. Why is the atomic weight of sulfur not a whole number?
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T
3. Research radioisotopes and briefly state the uses for carbon, cobalt and iodine (in carbon
dating and medicine)
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4. Briefly outline the some dangers of using radioisotopes
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Extension:
Create a timeline for the history of the theories of the atom and its structure. Include the dates,
people and what they theorized or discovered.
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Topic 2.1 The Atom Extra Worksheet
Complete the following table
Name of
element
Symbol
Atomic
Number
(Z)
Mass
Number
Number of
Protons
Number of
Neutrons
Number of
Electrons
H
Mg
8
11
27
14
Be2+
26
24
Si
Sr
17
18
1. Until 1897, chemists accepted the theory that the atom was the smallest particle of matter
obtainable. Atoms were believed to be individual particles. Now we know that the atom is
composed of at least three kinds of particles: _______________________, electrically
negative; _______________________, electrically positive; and
_______________________, electrically neutral.
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2. According to the modern picture of an atom, it consists of a very dense central portion, called
the _______________________, surrounded by _______________________ that make up the
volume of the atom but add little to its _______________________ .
3. Every atom of the same element has the same number of _______________________ in its
nucleus, although the number of _______________________ may vary.
4. All atoms of the same element have the same (atomic number, mass number)
_______________________..
5. The mass number of the atom of an atom is equal to the number of _______________________
plus the number of _______________________ in the nucleus of the atom.
6. If the mass number of the atom of a given element is known, the number of neutrons in its nucleus
can be calculated by subtracting the _______________________ from the
_______________________. For example, if an atom of the element sodium, atomic number 11, has a
mass of 23, the atom has _______________________ neutrons.
7. Isotopes of a given element have a (different, the same) _______________________ atomic
number.
8. Three isotopes of magnesium have mass numbers of 24, 25, and 26 have been discovered. The
atomic number of magnesium is 12. In the spaces below, diagram only the nuclear structure of each
isotope, as shown for magnesium-24.
9. In the space below make diagrams showing the nuclei of the three isotopes of uranium, atomic
number 92, having mass numbers 234, 235, and 238.
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Topic 2.2 The Mass Spectrometer
1. Draw a simple diagram of a mass spectrometer
2. Describe how in the mass spectrometer:
a. The atoms are converted into ions.
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__________________________________________________________________
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b. The ions of different masses are separated.
__________________________________________________________________
__________________________________________________________________
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c. The ions are detected.
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Study Hint
The atomic mass for each element is reported on the periodic table. This number is a weighted
average of the masses of each of the isotopes of an element. For example, the atomic mass of carbon
is reported as 12.011 amu. Carbon is composed primarily of two isotopes:
carbon-12
and carbon-13. The atomic mass is calculated from the relative
abundance
and the masses for these two isotopes. Using the equation below we can
calculate the
atomic mass for carbon.
Carbon-12 makes up 98.93% of all of the carbon atoms, while carbon-13
is about
1.07% abundant. Since the carbon-12 isotope is more abundant, its
mass is weighted more in the calculation of carbon’s atomic mass. An example calculation is done below.
Example
What is the atomic mass (the weighted average mass) for carbon?
Isotope
Carbon-12
Carbon-13
% Abundance
98.93%
1.07%
Mass
12.000 amu
13.003 amu
- substitute values in equation: (convert % to decimals)
atomic mass = (0.9893)×(12.000amu) + (0.0107)×(13.003amu)
- calculate:
atomic mass = 12.01 amu
Steps for Calculating Average Atomic Mass
(When given percentages of each isotope and each isotopes mass)
1. Convert the percentages into decimals. (This percentage is known as its relative abundance or
percent abundance).
2. Multiply the percentage of each isotope by its respective mass.
3. Add the numbers from step two together.
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Steps for Calculating Percent Abundance
(When given molar masses of each isotope)
1. Because percent abundances will always add up to 100% (1), assign one isotope to have a
percentage of “x” and the other isotope to have a percentageof “1-x.”
2. Look up the average atomic mass of the atom on the periodic table.
3. Set up your problem so it looks like the setup below:
X•(Mass of Isotope A) + (1-X)•(Mass of Isotope B) = Average Atomic Mass
4. Solve for “X.” Multiply this number by 100 to turn it into a percentage. This is the percent
abundance of isotope A.
5. The percent abundance of isotope B is 100% minus the percent abundance of isotope A.
3. The element nitrogen has two isotopes with masses of 14 (99.5%) and 15 (0.5%). Calculate the
average atomic mass of nitrogen. (show your work)
4. The element chlorine has two isotopes with masses of 35 (75.5%) and 37 (24.5%). Calculate the
average atomic mass of chlorine. (show your work)
5. Calculate the atomic mass of an element which has two isotopes with
masses of 10 (20%) and 11 (80%). Show your work and name the element.
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6. Calculate the atomic mass of an element which has two isotopes with
masses of 12 (98.9%) and 13 (1.1%). Show your work and name the element.
7. Magnesium consists of three isotopes with masses of 24 (78.5%), 5 (10%),
and 26 (11.5%).What is the atomic mass of magnesium? (show your work)
8. Naturally occurring rubidium is 72.17% 85Rb (at.mass = 84.912 amu). The
remaining atoms are 87Rb (at. mass = 86.909 amu). Calculate the atomic
mass of Rb. 85.47 amu
9. The mass spectrum of an element shows that 78.99% of the atoms have a
mass of 23.985 amu, 10.00% have a mass of 24.986 amu and the remaining
11.01% have a mass of 25.982 amu.
a) Calculate the atomic mass of this element. 24.30 amu
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b) Give the symbol for each of the isotopes present.
10.
Antimony occurs naturally as two isotopes, one with a mass of 120.904
amu and the other with a mass of 122.904 amu.
a) Give the symbol that identifies each of these isotopes.
b) Use the atomic mass of antimony from the periodic table to calculate
121
the natural abundance of each of these isotopes.
Sb 57.5%
123
Sb 42.5%
11. Argon has three naturally occurring isotopes: argon-36, argon-38, and
argon-40. Based on argon’s reported atomic mass, which isotope do you
think is the most abundant in nature? Explain.
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12.
Copper is made of two isotopes. Copper-63 is 69.17% abundant and it
has a mass of 62.9296 amu. Copper-65 is 30.83% abundant and it has a
mass of 64.9278 amu. What is the weighted average mass of these two
isotopes?
13.
Calculate the atomic mass of silicon. The three silicon isotopes have
atomic masses and relative abundances of 27.9769 amu (92.2297%),
28.9765 amu (4.6832%) and 29.9738 amu (3.0872%).
14.
Calculate the atomic mass of silicon. The three silicon isotopes have
atomic masses and relative abundances of 27.9769 amu (92.2297%),
28.9765 amu (4.6832%) and 29.9738 amu (3.0872%).
15.
Gallium has two naturally occurring isotopes. The mass of gallium-69
is 68.9256 amu and it is 60.108% abundant. The mass of gallium-71 is
70.9247 amu and it is 39.892% abundant. Find the atomic mass of gallium.
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16.
Bromine has two naturally occurring isotopes. Bromine-79 has a mass
of 78.918 amu and is 50.69% abundant. Using the atomic mass reported on
the periodic table, determine the mass of bromine-81, the other isotope of
bromine.
17.
. Calculate the atomic mass of lead. The four lead isotopes have
atomic masses and relative abundances of 203.973 amu (1.4%), 205.974
amu (24.1%), 206.976 amu (22.1%) and 207.977 amu (52.4%).
18.
Antimony has two naturally occurring isotopes. The mass of antimony121 is 120.904 amu and the mass of antimony-123 is 122.904 amu. Using the
average mass from the periodic table, find the abundance of each isotope.
(Remember that the sum of the two abundances must be 100).
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2,8,6
Sulphur
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What do you notice about the number of outer shell electron in the last column?
What do you notice about the number of outer shell electrons and the column?
What do you notice about the number of shells and the row?
Questions
Use ‘x’ to represent electrons on the shells.
example (include the name and the numerical representation).
Fill in the electron shells for the first 20 elements as shown in the
Electron Configuration
Electromagnetic spectrum questions.
Read the information. Then type your answers in the spaces provided and then
print out the finished sheet to give to your teacher.
Electromagnetic waves are transverse waves. Although we cannot see their
vibrations theses are at right angles to the direction of wave travel. They also
travel very fast. In empty space there is nothing to slow them down and they all
travel at the same speed. Their speed is 300 million metres per second!
Gamma
rays
X-rays
ultraviolet Visible
light
Short wavelength, high frequency
infrared
microwaves
radio
waves
long wavelength, low frequency
1. Which colour of light has the longest wavelength?
2. Which type of electromagnetic wave has the longest wavelength?
3. What can be used to split visible light into the colours of the spectrum?
4. How fast to radio waves travel in empty space?
5. If a spacecraft sent some radio waves and some microwaves through space
to Earth, which would get there first?
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6. Which electromagnetic waves have a shorter wavelength than that of
light?
7. Which type of electromagnetic wave has the shortest wavelength?
8. Which colour of light is next to infrared waves in the electromagnetic
spectrum?
9. Which type of wave is next to violet light in the electromagnetic spectrum?
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Line Spectra
1) Below is a depiction of the Bohr model of the hydrogen atom.
a)
b)
c)
d)
e)
Label G as an electron in the ground state.
Label L the largest absorption of energy possible by an electron for this atom.
Label S the lowest energy gap.
Label J, the jump that will produce the highest frequency energy.
Why would an emission line spectrum for this atom show closer and closer together lines?
2) Below is a typical line spectrum.
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a) Briefly, how is a line spectrum produced?
b) Assuming that this spectrum results in the hydrogen atom finishing in the ground state, dra
w a sketch showing how the second lowest frequency line was produced.
c) How does the speed of the produced radiation change from high to low frequency?
d) Give 2 methods to excite substances enough that they will emit light.
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Spectral Lines, The Bohr Model and Quantum Theory
Introduction
You've just completed the four-part experiment on Spectroscopy where you've seen the
visible light spectra of different light sources, seen the emission spectra of different
elements and even calculated the wavelength of the major colors in the spectra. Did you
wonder where these spectra come from?
Asked yourself how are they created and why are they all different?
These are excellent questions and ones that some rather famous people asked themselves too.
The Investigation
Start at:
http://www.colorado.edu/physics/2000/quantumzone/index.html
Then go to:
Table of Contents ! Science Trek ! Quantum Atom (Spectral Lines)
As you progress through the readings, answer these questions:
1. What can be done with sunlight?
2. What did scientists see when they looked at bright light coming off an element like
hydrogen?
2. Pick three elements and draw their spectra. Describe how they are the same and
different.
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3. What puzzle did Niels Bohr come up with the solution to?
4. What was his solution?
5. Describe what happens when you click on different orbits in the model of the atom.
6. Why was Bohr's model so radical?
7. What is this kind of Physics called?
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8. Where are electrons located?
10. Bigger ____________10a = ______________ _____________10b.
10. Describe the detour to the Schrödinger Atom.
11. Why does thinking about energy levels make sense?
12. If the energy goes ___________13a, the extra energy appears as a ___________
13b. And for the electron to get ___________13c energy, it needs to
_____________13d a photon.
13. Explain how the atomic spectrum of an element is created.
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15. What are two uses of knowing about Einstein's Legacy?
The Conclusion
Summarize what you've learned about an atom and how the atomic spectrum of an element is
produced.
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Exam Questions
1.
How many protons, neutrons and electrons are present in each atom of 31P?
Protons
Neutrons
Electrons
A.
16
15
16
B.
15
16
15
C.
15
31
15
D.
16
31
16
(Total 1 mark)
2.
Which is correct for the following regions of the electromagnetic spectrum?
Ultraviolet (UV)
Infrared (IR)
A.
high energy
short wavelength
low energy
low frequency
B.
high energy
low frequency
low energy
long wavelength
C.
high frequency
short wavelength
high energy
long wavelength
D.
high frequency
long wavelength
low frequency
low energy
(Total 1 mark)
3.
What is the atomic number of a neutral atom which has 51 neutrons and 40 electrons?
A.
40
B.
51
C.
91
D.
131
(Total 1 mark)
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4.
What is the relative atomic mass of an element with the following mass spectrum?
A.
24
B.
25
C.
26
D.
27
(Total 1 mark)
5.
Which gives the correct order of these processes in a mass spectrometer?
A.
ionization
deflection
acceleration
B.
ionization
acceleration
deflection
C.
acceleration
ionization
deflection
D.
deflection
acceleration
ionization
(Total 1 mark)
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6.
Which species have the same number of electrons?
I.
S2–
II.
Cl–
III.
Ne
A.
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
(Total 1 mark)
7.
The table below shows the number of protons, neutrons and electrons present in five species.
Species
Number of protons
Number of neutrons
Number of electrons
X
6
8
6
Y
7
7
7
Z
7
7
8
W
8
8
8
Q
8
10
8
Which two species are isotopes of the same element?
A.
X and W
B.
Y and Z
C.
Z and W
D.
W and Q
(Total 1 mark)
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8.
Describe the emission spectrum of hydrogen. Outline how this spectrum is related to the energy levels in
the hydrogen atom.
................................................................................................................................................
................................................................................................................................................
................................................................................................................................................
................................................................................................................................................
................................................................................................................................................
................................................................................................................................................
(Total 3 marks)
9.
(i)
Describe and explain the operation of a mass spectrometer.
(5)
(ii)
State three factors that affect the degree of deflection of ions in a mass spectrometer.
(3)
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(iii)
Strontium exists as four naturally-occurring isotopes. Calculate the relative atomic mass of strontium
to two decimal places from the following data.
Isotope
Percentage abundance
Sr-84
0.56
Sr-86
9.90
Sr-87
7.00
Sr-88
82.54
(2)
(Total 10 marks)
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Exam Question Markscheme
1.
B
[1]
2.
A
[1]
3.
A
[1]
4.
A
[1]
5.
B
[1]
6.
A
[1
7.
D
[1]
8.
series of lines/lines;
electron transfer/transition between higher energy level to lower energy level /
electron transitions into first energy level causes UV series / transition into second
energy level causes visible series / transition into third energy level causes
infrared series;
convergence at higher frequency/energy/short wavelength;
Allow any of the above points to be shown on a diagram.
3
[3]
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9.
(i)
(ii)
(iii)
a vaporized sample must be used;
bombarded with (high energy) electrons to form positive ions;
accelerated by passing through an electric field;
deflected by passing through a magnetic field;
detected by producing a current;
Award [2 max] if just the words vaporization, ionization, acceleration,
deflection and detection are used with no explanation.
(size of the positive) charge (on the ion);
mass (of the ion);
strength of the magnetic field;
velocity/speed (of the ions) / strength of electric field;
m/z scores the first two marking points.
[(0.56 × 84) + (9.90 × 86) + (7.00 × 87) + (82.54 × 88)]
;
100
= 87.71;
Award [1 max] if answer not given to two decimal places.
Award [2] for correct final answer.
Apply –1(U) if answer quoted in g or g mol–1.
5
3 max
Ar =
2
[10]
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