Download Honors Chemistry Worksheet – Atomic Theory and the Basic Atom

Honors Chemistry Worksheet – Atomic Theory and the Basic Atom ANSWER KEY
NEATLY, provide the best, complete, detailed, yet concise response to each of the
following questions or problems. For problems, show all equations, work, units,
significant figures, and labels. Use dimensional analysis whenever possible.
1. What evidence showed that the particles in the beam of a Crookes’ tube were
negatively charged?
The particles were repelled from the negatively charged palate of an
electrical field.
2. Suppose two beams pass between a pair of oppositely charged plates. One of
the beams is composed of electrons, and the other is composed of protons. Will
the two beams bend in the same direction or in opposite directions? Why?
The two beams will bend in opposite directions. The protons will be
repelled from the positive electrode and attracted to the negative
electrode. The electrons will be repelled from the negative electrode and
attracted to the positive electrode.
3. What main feature of Dalton’s atomic model was abandoned after Thomson’s
discoveries?
The belief that the atom was indestructible and indivisible.
4. Make a diagram of a lithium atom, based upon Thomson’s atomic model.
The atom has a uniform mass of positive three charge spread throughout
with three electrons imbedded.
5. Suppose that a lithium atom lost one electron, forming a positive ion. How
would the drawing in question #4 be changed?
There would only be two electrons embedded in the uniform mass of three
positive charges.
6. Make a drawing to illustrate the paths of alpha, beta, and gamma radiation
as they pass between two oppositely charged plates. Make sure the plates are
labeled positive and negative accordingly.
7. What unexpected result did Rutherford’s gold foil experiment produce?
The scant few (1 in about 8,000) alpha particles that were deflected at
very large angles, in essence being bounced backwards.
8. According to Rutherford’s atomic model, why is most of an atom’s mass
located in its nucleus?
There had to be an extremely “massive” or dense region to the atom in
order to withstand the contact by the alpha particles and bounce it
backward.
9. List two ways that a proton differs from an electron.
Protons have a positive charge and a mass of 1.007 3 a.m.u. while
electrons have a negative charge and very little mass, 0.000 548 a.m.u.
10. Which subatomic particle determines a specific element?
The number of protons determines the identity of each element.
11. What is the mass number of an element that contains 20 protons and 22
neutrons?
The mass number, A is the sum of protons and neutrons. Therefore, A =
#p+ + #n0 = 20 p+ + 22 n0 = 42
12. How do the isotopes of oxygen (16O;
These three isotopes differ in
16O has a mass of 15.994 915
17O has a mass of 16.999 131
18O has a mass of 17.999 159
17O; 18O)
differ from one another?
mass and in number of neutrons.
a.m.u. and 8 neutrons.
a.m.u. and 9 neutrons.
a.m.u. and 10 neutrons.
13. Write the symbol for calcium-41, including its mass number and atomic
number (isotopic form).
4120Ca
14. An atom of zinc has an atomic number of 30 and a mass of 65. How many
protons, neutrons, and electrons are present in the zinc atom?
The zinc nuclide has 30 protons, 35 neutrons, and 30 electrons.
15. How many neutrons are in the following isotopes?
a. 10847Ag
b. 5324Cr
c.9440Zr
a. 61 neutrons
d. 52 neutrons
b. 29 neutrons
d.
9240Zr
c. 54 neutrons
Honors Chemistry Worksheet – Atomic Theory and the Basic Atom Pg. 2
16. Imagine that a beam of calcium-40 ions and beam of calcium-42 ions both
pass through a magnetic field. Assume that the ions have the same velocities
and charges. Which beam would be deflected more? Explain your reasoning.
Remember; momentum is equal to mass times velocity (mv). The calcium
– 40 ions would be deflected to a greater extent as their momentum is less
than that of the calcium – 42 ions. The calcium – 42 ions would have a
greater inertia, meaning there would be less force from the field with
which to accelerate the ion as compared to calcium – 40 whose inertia is
less and would undergo greater acceleration by the same force.
17. Suppose that a beam passing between a pair of charged plates had some
sulfur-32 ions with one extra electron and some sulfur-32 ions with two extra
electrons. If all the ions had the same velocity, which particles would be
deflected more? Explain your rationale.
Remember; momentum is equal to mass times velocity (mv). The sulfur
ion with a negative two charge would be deflected to a greater extent as
both mass and velocity of the particles are the same, making momentum
and inertia the same. However, Coulomb’s law would indicate the
electrostatic force would be greater for the ion of greater charge as
electrostatic force is directly related to quantity of charge by the
relationship: fel = k Q1Q2 / r2. This greater force would cause greater
acceleration in the path of the ion with greater charge.
18. Which would be bent more by a magnet – a beam of sodium ions or a beam
of potassium ions? Assume that all ions have identical charges and velocities.
Explain your reasoning.
Remember; momentum is equal to mass times velocity (mv). The sodium
ions would be deflected to a greater extent as their momentum is less
than that of the potassium ions. The potassium ions having a mass of
39.10 a.m.u. would have a greater inertia, meaning there would be less
force from the field with which to accelerate the ion as compared to
sodium ions with a mass of 22.99 a.m.u. whose inertia is less and would
undergo greater acceleration by the same force.
19. Which would be bent more by a magnet, a beam of neutrons or a gamma
ray? Justify your answer.
Neither as gamma rays possess no charge and neutrons possess no charge
meaning neither would interact with the applied magnetic field.
20. Two beams of ions; germanium – 74 and selenium – 74 pass between a pair
of charged plates. The ions have the same charge, but the velocity of the
germanium ions is twice as large as the velocity of the selenium ions. Identify
which beam will be deflected more. Support your response.
Remember; momentum is equal to mass times velocity (mv). The
selenium - 74 ions would be deflected to a greater extent as their
momentum is less than that of the germanium - 74 ions. The germanium 74 ions would have a greater inertia due to their greater velocity,
meaning there would be less force from the field with which to accelerate
the ion as compared to selenium - 74 whose inertia is less due to a lower
velocity and would undergo greater acceleration by the same force.
21. Two beams of ions, one containing calcium – 40 ions with a 1 + charge and
the other containing argon – 40 ions with a 1 – charge, both travel at the same
velocity. Explain how these two beams would be deflected if they passed
through an electrical field.
The two beams would be deflected to the same extent but in opposite
directions. The beams have the same momentum due to identical masses
and velocities and thus have the same inertia. The field strength being
the same would accelerate each beam to the same extent, but because the
charges are opposite the beams will be deflected in opposite directions.
22. Make a drawing showing the deflection of these beams when passed
through a pair of charged plates. Assume all velocities are equivalent.
a. sulfur – 34 ions with a 2 – charge and oxygen – 16 ions with a 2 – charge
b. 52Cr2+ ions and 52Cr5+
c. chlorine- - 37 ions with a – 1 charge and potassium – 37 ions with a + 1
a.
++++++++++
16
O2-
32 2-
S
-- ------- -
b.
++++++
52Cr+2
_- - - - - - -
52Cr5+
c.
+++++
37Cl137K+
-----
23. List the experimental facts known to Thomson, but not known to Dalton,
that led to the modification of Dalton’s model of an atom.
With the discovery of the electron, Thomson knew the atom to be
DIVISIBLE, not indivisible as Dalton believed And, he knew the atom to
have an electrical character or nature.
24. Use Dalton’s model of the atom to explain why sodium chloride is always
39.3 % sodium and 60.7 % chlorine by mass.
Dalton assumed all matter to be made up of atoms, and that atoms of a
given element are identical to one another and those of different
elements were distinctly different. Dalton stated that atoms were not
created nor destroyed in reactions, but rearranged by combining in small
whole numbers with other elements. Thus, he incorporated Proust’s law of
definite proportions (constant composition) into his theory which stated
that; “compounds are composed of elements combined in a fixed ratio by
mass.” Since the mass of sodium is 22.99 and the mass of chlorine is
35.45, sodium chloride; containing one ion of sodium and one ion of
chlorine would have a mass of 58.44. Therefore, dividing the mass
contribution of each element by the mass of sodium chloride would
continually produce the same percentage composition.
25. Use Dalton’s model of the atom to explain why calcium chloride is always
36.1 percent calcium and 63.9 percent chlorine by mass.
Dalton assumed all matter to be made up of atoms, and that atoms of a
given element are identical to one another and those of different
elements were distinctly different. Dalton stated that atoms were not
created nor destroyed in reactions, but rearranged by combining in small
whole numbers with other elements. Thus, he incorporated Proust’s law of
definite proportions (constant composition) into his theory which stated
that; “compounds are composed of elements combined in a fixed ratio by
mass.” Since the mass of calcium is 40.08 and the mass of chlorine is
35.45, calcium chloride; containing one ion of calcium and TWO ions of
chlorine would have a mass of 110.98. Therefore, dividing the mass
contribution of each element by the mass of calcium chloride would
continually produce the same percentage composition.
26. Which aspects of Dalton’s model of the atom became outdated after
Thomson’s cathode ray experiments?
Atoms were no longer considered indivisible and indestructible. The
smallest particle of matter was now the electron.