Honors Chemistry Worksheet – Atomic Structure
Provide the best, complete, detailed, and concise response to each of the following
questions/problems. Write neatly on a separate sheet of paper. Use the text chapters on
atomic structure and electronic configuration/structure to assist in answering.
1. What is the modern atomic theory?
2. What are the main parts of an atom? What particles are found in each part?
Describe in detail each type of particle.
3. How does the size of the nucleus of an atom compare with the size of an atom?
4. What is an energy level or shell?
5. Describe a hydrogen atom
6. What is an atomic mass unit? If you know the number and kinds of particles in an
atom, how can you calculate its mass number?
7. What is the atomic number of an atom?
8. How do you calculate the number of neutrons in the nucleus of an atom?
9. An atomic nucleus contains 6 protons and 6 neutrons. About the nucleus move 2
electrons in the K shell and 4 electrons I the L shell. What is the atomic number of
the atom? What is its mass number? What is the name of the atom?
10. What are isotopes?
11. What is the atomic weight of an element?
12. What element is the current standard for the atomic weight scale?
13. What did each of the following contribute to the atomic theory?
a. Dalton
e. Moseley
b. Thomson
c. Rutherford
d. Chadwick
14. List the major points of Dalton’s atomic theory. Are any of Dalton’s postulates
still in existence? Have any been modified or discarded? If so, which and how?
15. How would you show the law of conservation of mass with a burning candle?
16. How could one show that there are two kinds of charged particles?
17. Since alpha and beta particles cannot be seen, even with a microscope, how are
they detected?
18. Discuss/explain the results of the Rutherford gold foil experiment.
19. Criticize the statement: An element is a substance made up of atoms all of which
are alike.
20. Calculate the kinetic energy of an alpha particle with a velocity of 10,000. miles
per second. It has a mass of 4.00 amu. One atomic mass unit s equivalent to
1.6605 x 10 – 24 g.
21. Explain the law of multiple proportions.
22. Who developed the law of constant composition (definite proportions)? To what
does it apply?
23. What is an ion? How are atomic cations formed? How are atomic anions formed?
24. Which would be bent more by a magnet; gamma rays or a beam of neutrons?
Explain your reasoning.
25. What is the quantity of electrical charge on an electron? Who determined this
charge? How was this charge determined? Brief description may be found at
http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::100%::100%::/sites/dl/free/007251264
4/117354/02_Millikan_Oil_Drop.swf::Milikan%20Oil%20Drop or
http://glencoe.com/sec/science/physics/ppp_09/animation/Chapter%2021/Millika
ns%20Oil-Drop%20Experiment.swf
26. What was the value determined by Thomson for the charge to mass ratio of the
electron? How did he determine this value? How was this useful in determining
the mass of the electron?
27. What instrument is used to detect the different isotopes of an element? Most of
the ions passing through this instrument exhibit what charge? How can the
average atomic mass be determined using this instrument?
28. Use Dalton’s model of the atom to explain why magnesium bromide is always
13.20 % magnesium and 86.80 % bromine. How did Dalton incorporate Proust’s
Law of Definite Proportions (Law of Constant Composition) into his atomic
theory?
29.
Honors Chemistry Worksheet – Atomic Structure
Answer Key
Provide the best, complete, detailed, and concise response to each of the following
questions/problems. Write neatly on a separate sheet of paper. Use the text chapters on
atomic structure and electronic configuration/structure to assist in answering.
1. What is the modern atomic theory?
The atom possesses a very small, very dense, positively charged core called the
nucleus. It is composed of nucleons, the major ones being protons and neutrons.
The electrons travel randomly around the nucleus in energetically permissible
regions which make up the electron cloud.
2. What are the main parts of an atom? What particles are found in each part?
Describe in detail each type of particle.
There are two main parts to an atom; the nucleus and the electron cloud.
The nucleus is the center or core of the atom containing most of the atom’s mass.
The nucleus is also positively charged as it contains the protons which have a
mass of 1.007 3 a.m.u. or 1.673 x 10-24 g and a standardized charge of +1. The
nucleus also contains the neutral particles called neutrons that have a mass of
1.008 7 a.m.u. or 1.678 x 10-24 g and a charge of zero (0).
The electron cloud contains rapidly moving electrons which have very little
mass; 0.000 549 a.m.u. or 9.11 x 10-28 g and a standardized charge of -1.
3. How does the size of the nucleus of an atom compare with the size of an atom?
The nuclear diameter is about 10-4 the diameter of the atom.
4. What is an energy level or shell?
The pathways taken by electrons as they move around the nucleus make up an
energy level or shell. These energy levels or shells increase in energy moving
away from the nucleus.
5. Describe a hydrogen atom.
A hydrogen atom is composed of one electron and one proton. It has a mass
number of one (A = 1) and an average atomic mass of 1.007 95 a.m.u.
6. What is an atomic mass unit? If you know the number and kinds of particles in an
atom, how can you calculate its mass number?
An atomic mass unit (a.m.u.
7. What is the atomic number of an atom?
The atomic number of an atom (element) indicates the number of protons found
within the nuclei of the element’s atoms.
8. How do you calculate the number of neutrons in the nucleus of an atom?
The number of neutrons in an isotope may be determined by subtracting the
number of protons (atomic number) from the mass number. #n0 = A - Z. If
working with the element, the atomic mass may be rounded to a whole number
and used as a mass number.
9. An atomic nucleus contains 6 protons and 6 neutrons. About the nucleus move 2
electrons in the K shell and 4 electrons in the L shell. What is the atomic number of
the atom? What is its mass number? What is the name of the atom?
The atomic number, Z, is 6. The mass number of the isotope, A, is 12 obtained
from A = Z + #n0. The element is carbon.
10. What are isotopes?
Isotopes are atoms of the same element that differ in mass. These mass
differences are a result of different numbers of neutrons.
11. What is the atomic weight of an element?
The atomic weight of an element or atomic mass of an element is the average of
all naturally occurring isotopes and their weighted abundance.
12. What element is the current standard for the atomic weight scale?
The current standard for the atomic mass scale is the carbon – 12 isotope which
is assigned a mass of exactly 12.000 000 000…. a.m.u. Prior standards were
oxygen – 16 and
13. What did each of the following contribute to the atomic theory?
a. Dalton
f. Moseley
b. Thomson
c. Rutherford
d. Chadwick
a. Developed the first comprehensive atomic theory.
b. Discovered the electron and its charge to mass (e/m) ratio. Leads to the atom
being divisible and having an electrical character.
c. Performed the gold foil experiment leading to the nuclear atom. The atom has
a positive, massive or dense core or center to the atom.
d. Discovered the neutron, an electrical neutral particle with a substantial mass.
e. Determined the atomic numbers of many elements. This permitted the
identification of many elements with respect ot the number of protons in their
nuclei.
14. List the major points of Dalton’s atomic theory. Are any of Dalton’s postulates
still in existence? Have any been modified or discarded? If so, which and how?
1) Elements are composed of tiny indestructible particles called atoms
2) Atoms of the same element are identical in properties including mass.
3) Atoms of different elements are distinctly different in properties including
mass.
4) A chemical reaction involves the separation, combination, or rearrangement
of atoms; it does NOT result in their creation or destruction.
5) Compounds are composed of atoms of more than one element. The atoms of a
given compound are combined in a fixed numerical ratio.
2) has been modified with the discovery of isotopes – properties are the same,
but atoms of the same element may have different masses.
1) has been modified as atoms are divisible or can be broken down.
A Note: While atoms aren’t changed through chemical reaction, they can be
changed through nuclear change.
15. How would you show the law of conservation of mass with a burning candle?
Mass a candle. Place the candle in a sealed chamber and obtain the mass of both.
Ignite the candle inside of the sealed chamber and allow it to burn. When the
candle stops burning (extinguished) mass the chamber and candle again. Then
mass the candle. If the candle has decreased in mass, but the chamber has
retained its mass, then the candle, then mass is conserved.
16. How could one show that there are two kinds of charged particles?
If the two particles were passed through a magnet or electrical field, the particles
would be deflected in opposite directions if they had different charges.
17. Since alpha and beta particles cannot be seen, even with a microscope, how are
they detected?
These particles are detected by placing a radioactive substance in a unit such as
a cloud chamber. Once the particles have been observed, then tests may be run
to determine charge and mass of the particles similar to the determination of
charge and mass of the electron.
They may also be detected using a fluorescent material.
18. Discuss/explain the results of the Rutherford gold foil experiment.
Most of the alpha particles passed through the foil without deflection because the vast majority
of the atom is empty space with a few electrons in it
The few alpha particles deflected at minor angles came close to a small bundle or core of
positive charge which were, therefore, repelled
The scant number of alpha particles being bounced back was a result of an almost direct
collision with a very massive (extremely dense) and positively charge region occupying a very
small volume
19. Criticize the statement: An element is a substance made up of atoms all of which
are alike.
The number of protons and electrons of the atoms on an element are the same in
number. However, the number of neutrons may vary between atoms of the same
element meaning the element has isotopes. These isotopes differ in mass due to
the differing number of neutrons.
20. Calculate the kinetic energy of an alpha particle with a velocity of 10,000. miles
per second. It has a mass of 4.00 amu. One atomic mass units equivalent to 1.660 5 x
10 – 24 g.
K.E. = ½ mv2
10,000. mi. x 5,280 ft x 12 inches x 2.54 cm x 10-2 m = 1.609 344 x 107 m
1 mile
1 foot
1 inch
1 cm
= ½ [4.00 a.m.u x
1.660 5 x 10-24 g x 1 kg ] x (1.609 344 x 107 m)2
1 a.m.u.
10+3 g
= 8.57 x 10-13 kgm2/s2 x
1J
= 8.57 x 10-13 J
1 kgm2/s2
21. Explain the law of multiple proportions.
The law of multiple proportions when two elements combine with each other to
form more than one compound, the weights of one element that combine with a
fixed weight of the other are in a ratio of small whole numbers.
Compound
Ratio of Mass O
To N
Masses to fixed
mass N
N2O
16.00 u O
28.02 u N
0.5710 u O
uN
÷ 0.5710
=1
NO
16.00 u O
14.01 u N
1.142 u O
uN
÷ 0.5710
=2
N2O3
48.00 u O
28.02 u N
1.713 u O
uN
÷ 0.5710
= 3
NO2
N2O5
22. Who developed the law of constant composition (definite proportions)? To what
does it apply?
Joseph Proust developed the Law of Constant Composition also called the Law
of Definite Proportions. The law pertains to compounds. It states that
compounds are composed of elements combined in a fixed ratio by mass.
23. What is an ion? How are atomic cations formed? How are atomic anions formed?
An ion is any electrical charged particle such as an electron, a proton, an atom
possessing a net charge or group of atoms possessing a charge.
Atomic cations are formed when an atom loses one or more electrons.
Atomic anions are formed when an atom gains one or more electrons.
24. Which would be bent more by a magnet; gamma rays or a beam of neutrons?
Explain your reasoning.
Because neither gamma rays nor neutrons possess an electrical charge, neither
would be affected by a magnetic field.
29. What is the quantity of electrical charge on an electron? Who determined this
charge? How was this charge determined? Brief description may be found at
http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::100%::100%::/sites/dl/free/007251264
4/117354/02_Millikan_Oil_Drop.swf::Milikan%20Oil%20Drop or
http://glencoe.com/sec/science/physics/ppp_09/animation/Chapter%2021/Millika
ns%20Oil-Drop%20Experiment.swf
The quantity of electrical charge on an electron as determined by Robert Millikan is
1.602 x 10-19C. It is a negative charge.
Millikan performed the oil drop experiment in which he atomized oil into droplets
and ionized them by ionizing air molecules with x-rays. The droplets fell between
electrically charged plates. Using terminal velocity and accounting for the viscous
nature of air Millikan was able to determine the mass and velocity of the oil droplet.
Using a uniform electrical field to oppose the gravitational field acting on the
droplet, Millikan was able to establish the charge on each droplet investigated. He
found that while the total charge on each droplet varied, but the charges were all
multiples of a single smallest charge. He correctly believed that smallest value to be
the charge on a single electron.
30. What was the value determined by Thomson for the charge to mass ratio of the
electron? How did he determine this value? How was this useful in determining
the mass of the electron?
The charge to mass ratio of the electron is 1.759 x 108 C/g.
Thomson used a CRT with both a magnetic field and a perpendicularly aligned
electrical field. The magnetic field altered the path of the cathode ray (electrons).
By adjusting the voltage on the electrical field, Thomson was able to counteract
or cancel out the effect of the magnetic field. By setting the field strengths equal
to one another, he was able to determine the electron’s charge to mass.
By combining the charge to mass ratio of the electron with the charge of the
electron, the mass of the electron could be determined.
e ÷ e/m = e x
m = 1.602 x 10-19 C x
1 g_____
e
1.759 x 108 C
= 9.107 x 10-28 g
31. What instrument is used to detect the different isotopes of an element? Most of
the ions passing through this instrument exhibit what charge? How can the
average atomic mass be determined using this instrument?
The mass spectrograph or mass spectrometer is the analytical instrument used to
determine isotope composition and abundance for an element. After the substance is
injected and vaporized it is exposed to an electron beam which forms mainly +1
ions. These are accelerated through a magnetic field which deflects their paths to
different extents pending on the mass to charge ratio of the ion. Number of hits on
the detector yields relative abundance while location of hits on the detector would
enable mass calculation. A sample of the element would be injected resulting in as
determination of the masses of isotopes present in the sample as well as their relative
abundance. The average atomic mass could then be determined using;
Ave. At. Mass = [(% abundance x isotope mass) + (% abundance x isotope mass) + …..]
Total %
32. Use Dalton’s model of the atom to explain why magnesium bromide is always
13.20 % magnesium and 86.80 % bromine. How did Dalton incorporate Proust’s
Law of Definite Proportions (Law of Constant Composition) into his atomic
theory?
Dalton stated:
Compounds are composed of atoms of more than one element. The atoms of a
given compound are combined in a fixed numerical ratio. He also stated that
atoms of a given element all had the same mass, therefore all magnesium atoms
weighed the same and all bromine atoms weighed the same. Since their
combining ratio was fixed in forming the compound magnesium bromide, the
respective mass of each element would be the same in the compound and
therefore, the mass percentages determined for the compound.
According to Dalton’s theory, a compound always has atoms of the same
elements combined in the same numerical ratio. Since atoms of an element have
a fixed mass, the mass contribution by each element to the mass of the
compound would always be the same due to the fixed ratio by which they
combine.