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. Draw diagrams of the Thomson models of the boron atom and the fluorine
atom.
Boron
fluorine
2. How can a neutral atom become an ion with a charge of 2-?
The neutral atom would have to capture or gain two electrons.
3. What subatomic change occurs when a neutral calcium atom becomes a
calcium 2+ ion?
The neutral calcium atom with 20 protons and 20 electrons would lose
two electrons leaving it with 20 protons and 18 electrons.
4. Compare the composition of a neutral sodium atom with that of a sodium +1
cation.
The neutral sodium atom would have 11 protons and 11 electrons,
possibly around 12 neutrons (isotope pending). The sodium cation would
have 11 protons and 10 electrons, possibly around 12 neutrons (isotope
pending).
Honors Chemistry Worksheet – Atomic Theory and the Basic Atom Pg. 2
5. Compare and contrast the following atoms or ions.
a. a barium – 137 atom and a barium – 137 cation with a 2+ charge
b. a molybdenum – 96 atom with a molybdenum – 96 cation with a +6
charge
c. a phosphorus – 31 atom and a phosphorus – 31 anion with a 3charge
a. The barium – 137 atom would have 56 protons, 56 electrons and 81
neutrons. The barium – 137 cation would have 56 protons, 54 electrons
and 81 neutrons.
b. The molybdenum – 96 atom would have 42 protons, 42 electrons, and
54 neutrons. The molybdenum - 96 +6 cation would have 42 protons, 36
electrons, and 54 neutrons.
c. The phosphorus – 31 atom would have 15 protons, 15 electrons, and 16
neutrons. The phosphorus – 31 anion would have 15 protons, 18
electrons, and 16 neutrons.
6. Identify the following ions as either cations or anions. Also, indicate the
number of electrons lost or gained from the neutral atoms.
a. Cl1-
b. Mg2+
c. S-2
d. Al+3
a. Cl1- is an anion having acquired (gained) one electron
b. Mg+2 is a cation having lost two electrons
c. S-2 is an anion having acquired two electrons
d. Al3+ is a cation having lost three electrons
7. List which of the three types of radiation; alpha, beta, or gamma; each of the
following describes.
a. is not deflected by a magnet - gamma
b. has a negative charge - beta
c. moves with the greatest speed - gamma
d. consists of ions – alpha and beta
e. is similar to light rays - gamma
f. consists of the same particles as cathode rays - beta
Honors Chemistry Worksheet – Atomic Theory and the Basic Atom Pg. 3
8. Compare and contrast the masses and charges of alpha, beta, and gamma
radiation.
Radiation
Alpha
Beta
Gamma
Mass
4 amu/6.644 x 10-24 g
0 amu/9.11 x 10-28 g
None
Charge
+2
1None
9. List the three types of radiation in order of decreasing penetrating ability.
Gamma
>
Beta
>
Alpha
10. List the two changes that Rutherford made in Thomson’s model of the atom
in order to explain why some alpha particles were deflected at very large angles
(bounced backwards).
Rutherford created an atomic model in which all of the protons (positive
charge) were gathered in a very small, dense core or center. This made the
core or center of the atom very “massive” or extremely dense.
11. Make a drawing of the Rutherford model of an atom of beryllium. Discuss
the limitations of the drawing.
The model drawn is not to scale.
Obviously, the atom is too small
to be seen and in addition, the
nucleus is 10-4 times smaller from
a diameter standpoint meaning it
would not even be seen as it is
here. The atom is actually three
dimensional but the model is only
two dimension. And lastly, the
electrons would be in constant
motion.
Honors Chemistry Worksheet – Atomic Theory and the Basic Atom Pg. 4
12. Make drawings of the Rutherford models of fluorine – 19 atom and a
sodium – 23 ion with a positive one charge.
e-
ee-
ee11p+1
2n0
eee-e-
e-eee-
13. Compare the number of fundamental particles in Dalton’s atomic theory to
the number of fundamental particles in Rutherford’s
atomic model.
eDalton’s atomic model had one fundamental particle, the atom for each
element. Rutherford’s model had two fundamental particles, the proton
and the electron proposed for each element.
14. What observations led scientists to suspect that there must be neutral
particles with about the same mass as protons in the nucleus of atoms?
Scientists could not account for the masses of atoms with just the masses
of the protons and electrons. Therefore, they were looking for a particle of
mass. And, since they had accounted for the neutrality of atoms with
protons and electrons, the particle would have to be neutral otherwise,
the atom’s natural state would have been one with an electrical charge.
15. Explain why most of the atom is empty space.
The mass of the atom was congregated in its core or nucleus leaving a
large amount of volume to house the extremely small but rapidly moving
electrons. The electrons motion appears to occupy as rather large volume
respectively, but where the electron is not physically, is empty space
16. A proton beam, an electron beam, and a neutron beam pass between two
charged plates. Assuming the velocities to be the same, draw a diagram
showing the paths of each type of subatomic particle.
17. In less massive atoms, the ratio of neutrons to protons is about one to one;
while in more ,massive atoms the ratio increases to about 1.5 to 1. Considering
the electric charges of these two subatomic particles, propose an explanation to
account for this change in the ratio.
The neutrons may serve to spread out the protons, increasing distance
between them, in order to reduce electrostatic repulsion and therefore
decrease energy in the nucleus. As the overall number of protons
increases, the greater the overall positive charge of the nucleus may
require a greater number of neutrons to spread the protons even further
apart in order to attain a sufficiently low energy.
18. Calcium has five stable isotopes. How do these isotopes differ from one
another? How are they similar?
The five stable isotopes of calcium would have the same number of
protons and electrons (assumes neutrality) which would be 20. The
number of neutrons for each isotope would differ from the rest.
19. Hydrogen – 1 is the only isotope whose atomic number equals its mass
number. What does this indicate about its composition?
The isotope protium, 11H, has no neutrons in its nucleus, only one major
nucleon, a proton. If neutral, it would have one electron.
20. An atom has 15 protons and 16 neutrons. What is the atomic number,
mass number, and the symbol of this element?
The atomic number, Z, is 15. The mass number, A, is 31. The symbol of
the element is P and the symbol of the isotope is 3115P.
21. Write the symbol (isotopic symbol), including atomic number and mass
number for the following isotopes.
a. helium – 3
d. molybdenum – 95
a.
e.
32He
23892U
b.
42He
b. helium – 4
e. uranium – 238
c.
137N
c. nitrogen – 13
d.
9542Mo
22. How are chlorine – 37 and calcium – 40 similar?
Both of these isotopes have 20 neutrons in their nuclei.
Chlorine – 37 :
Calcium – 40 :
#n0 = A - Z = 37 - 17 = 20 n0
#n0 = A - Z = 40 - 20 = 20 n0
23. Iodine – 131 is a radioactive isotope (radioisotope) often used in the
treatment of thyroid disorders. Write the symbol for this element, including the
atomic and mass numbers.
13153I