ATOMS: History of Atomic Theory & Isotopes
1.
Choose the letter of the chemist who proposed each of the ideas listed below. Each
letter may be used once, more than once, or not at all.
A. Democritus
B. Lavoisier
C. Proust
D. Dalton
a) Matter is neither created nor destroyed in chemical reactions.
b) A given compound always has the same relative numbers and kinds of atoms.
c) All atoms of a given element are identical, but they differ from those of any
other element.
d) A given compound always contains the same elements in the same proportions
by mass.
e) Each element is composed of extremely small particles called atoms.
f) All matter is composed of tiny, indivisible particles.
g) Atoms are neither created nor destroyed in chemical reactions.
2.
What definition of the atom is accepted by scientists today?
3.
Name the three scientific laws that provided basic evidence for Dalton’s atomic
theory.
4.
Does the law of definite proportions apply to elements or mixtures? Explain.
5.
State the four basic principles of Dalton’s atomic model.
6.
How did Dalton’s model account for the law of conservation of mass?
7.
How did Dalton’s model account for the law of definite proportions?
8.
Suppose a reaction occurs in which all reactants are completely consumed.
a) How does the mass of the products compare with the mass of the reactants?
b) Who first identified this relationship?
c) What law explains this relationship?
9.
Consider the compound ammonia (NH3).
a) Will samples of ammonia taken from different sources always contain the same
percentage, by mass, of nitrogen?
b) What law explains this relationship?
c) Who first identified this relationship?
10. What would Proust say about the composition of all samples of carbon dioxide
(CO2)?
11. What would Dalton say about the composition of all samples of carbon dioxide
(CO2)?
12. Explain the function of a scientific model.
13. Write the word(s) that best completes each statement.
a) The negatively charged electrode of a cathode ray tube is the _________________.
b) Rutherford’s experiment showed that the charge on the nucleus of the atom
must be _________________.
c) In his experiments with cathode ray tubes, Thomson concluded that cathode
rays were composed of particles that were _____________________ charged.
d) A stream of particles originating from a cathode is called a(n)
__________________.
e) The SI unit of electrical charge is the _____________________.
f) The negatively charged particle found outside the nucleus is the ______________.
g) The small core at the center of an atom containing a positive charge is the
_____.
h) _____________________ is credited with performing the oil drop experiment.
i) Millikan performed an experiment to measure the _______________ of an
electron.
j) _____________________ proposed the first atomic model that accounted for the
electrical nature of the atom.
k) _____________________ proposed that an atom was an indivisible sphere.
l) _____________________ developed the cathode ray tube.
m) _____________________ discovered the electron.
n) _____________________ proposed the existence of the nucleus of the atom.
o) _____________________ was the first person to identify the neutron.
p) _____________________ was the first subatomic particle discovered.
q) _____________________ used metallic foil as a target for alpha bombardment.
r) Thomson determined the __________________ for the electron and for the proton.
14. What was the purpose of Millikan’s oil drop experiment?
15. To calculate the mass of an electron, what information did Millikan need to use
from J. J. Thomson’s experiment?
16. How did Rutherford’s alpha-scattering experiment show that Thomson’s plum
pudding model of the atom was incorrect?
17. Draw and label a diagram of Rutherford’s atomic model. Draw and label a diagram
of Thomson’s atomic model. How do these two models differ?
18. Which component of atomic structure was inadequately explained by the
Rutherford model?
19. A fifth-grader tells you that the structure of the atom can be compared with the
solar system: “Just as the planets revolve around the sun, electrons revolve
around the nucleus.” Why is this comparison incorrect?
20. If matter is mostly empty space, why don’t you fall through the “holes” in the floor?
21. If the statement is true, write “True.” If the statement is false, change the
underlined word(s) to make the statement true.
a) The mass of an electron is approximately equal to the mass of a proton.
b) The atomic number is represented by the symbol Na.
c) The difference in mass of isotopes of the same element is due to the different
numbers of protons in the atom.
d) One atomic mass unit (amu) is equal to one-twelfth the mass of the carbon-12
isotope.
e) Moseley discovered that all atoms of an element have the same number of
neutrons in their nuclei.
f) In a neutral atom, the number of protons always equals the number of
electrons.
g) When an atom gains or loses one or more electrons, it is called an isotope.
h) Atoms with the same number of protons but different numbers of electrons are
called isotopes.
22. Write the nuclear symbol for each of the following neutral isotopes. Use the
periodic table to determine the number of protons, neutrons, and electrons in each
isotope.
a) chromium- 50
c) magnesium- 26
e) silicon- 29
b) chlorine- 37
d) iridium- 193
f) neon- 22
g) iodine-125
h) potassium-39
I)
iron-56
23. Identify each of the following elements by name.
a) 1 proton
c) 8 protons
b) 4 protons
d) 12 protons
e) 20 protons
f) 30 protons
24. Give the number of protons in the nucleus of each of the following elements.
a) uranium
c) helium
b) selenium
d) lawrencium
25. Give the number of neutrons in the nucleus of each of the following isotopes.
a) titanium-46
c) sulfur-34
b) nitrogen-15
d) copper-65
26. Write the nuclear symbol for each of the following ions.
a) 17 protons, 18 electrons, 17 neutrons
b) 3 protons, 2 electrons, 5 neutrons
c) 12 protons, 10 electrons, 11 neutrons
d) 8 protons, 10 electrons, 9 neutrons
27. Determine the number of protons and electrons in each of the following ions.
a) Cu2+
c) H1+
b) F1d) Na1+
28. Complete the table below for neutral isotopes.
Isotope
Atomic
Number
Mass
Number
calcium-43
Number of
Protons
Electrons
20
lead-211
plutonium-242
Neutrons
129
94
chromium-50
24
29. Complete the following table.
Subatomic Particle
Location
Charge
Mass (amu)
inside nucleus
0
0
30. How do the numbers of protons, neutrons, and electrons compare in two atoms of
the same element that are:
a) different isotopes?
b) different ions?
31. Suppose two atoms of oxygen have different numbers of neutrons.
a) What property of the two atoms will be different?
b) Will the chemical properties of the two atoms be affected?
32. Suppose two atoms of magnesium have different numbers of electrons.
a) What property of the two atoms will be different?
b) Will the chemical properties of the two atoms be affected?
33. Based upon what you now know about the modern model of the atoms, criticize
these statements from Dalton’s atomic theory of 1803:
a) Atoms are indivisible.
b) All atoms of the same element have the same mass.
34. When scientists discovered subatomic particles, disproving one of Dalton’s basic
ideas, why didn’t they discard the rest of Dalton’s theory?
35. Would “heavy water, 2H2O, taste different from regular water, 1H2O? Explain.
WORKSHEET:
Symbol
11
5
39
19
Atomic
Number
Number of
Protons
Number of
Neutrons
15
15
Number of
Electrons
Charge
B0
K+
56
56
26
Mass
Number
Isotopes & Ions
0
137
54
127
54
Fe 2+
10
208
82
10
10
16
18
1-
Pb 0
16
30
65
28
U0
235
92
238
92
3+
WORKSHEET:
1.
Average Atomic Mass
Based upon what you now know about the modern model of the atoms, criticize
these statements from Dalton’s atomic theory of 1803:
a) Atoms are indivisible.
_________________________________________________________________________________
_________________________________________________________________________________
b) All atoms of the same element have the same mass.
_________________________________________________________________________________
_________________________________________________________________________________
2.
When scientists discovered subatomic particles, disproving one of Dalton’s basic
ideas, why didn’t they discard the rest of Dalton’s theory?
_________________________________________________________________________________
_________________________________________________________________________________
3.
Would “heavy water, 2H2O, taste different from regular water, 1H2O? Explain.
_________________________________________________________________________________
_________________________________________________________________________________
4.
Although the atomic mass for zinc is listed as 65.39, there is no zinc atom with
that relative mass. Explain.
_________________________________________________________________________________
_________________________________________________________________________________
5.
There are two naturally occurring isotopes of copper (Z=29), copper-63 and copper65. The average atomic mass of copper on Earth is 63.546. Which of these
isotopes of copper is more abundant? Explain.
_________________________________________________________________________________
_________________________________________________________________________________
Imagine that a chemist is trying to establish whether a piece of rock is from a
meteorite that fell from outer space. The rock contains more copper-65 atoms than
copper-63 atoms. What can you conclude about the rock’s origin? Explain.
_________________________________________________________________________________
_________________________________________________________________________________
6.
Calculate the average atomic mass of chromium using the following spectroscopic
data.
Isotope
Mass (amu)
Percent Abundance
Chromium-50
Chromium-52
Chromium-53
Chromium-54
49.946
51.941
52.941
53.939
4.3500
83.800
9.5000
2.3500
WORKSHEET:
The History of the Atomic Model
1. On the line at the left, write the letter of the chemist who proposed each of the ideas
listed below. Each letter may be used once, more than once, or not at all.
A. Democritus
B. Lavoisier
C. Proust
D. Dalton
______
a) Matter is neither created nor destroyed in chemical reactions.
______
b) A given compound always has the same relative numbers and kinds of
atoms.
______
c) All atoms of a given element are identical, but they differ from those of
any other element.
______
d) A given compound always contains the same elements in the same
proportions by mass.
______
e) Each element is composed of extremely small particles called atoms.
______
f)
______
g) Atoms are neither created nor destroyed in chemical reactions.
All matter is composed of tiny, indivisible particles.
2. What definition of the atom is accepted by scientists today?
__________________________________________________________________________________
__________________________________________________________________________________
3. Name the three scientific laws that provided basic evidence for Dalton’s atomic
theory.
4.
a)
_____________________________________________________________________________
b)
_____________________________________________________________________________
c)
_____________________________________________________________________________
Does the law of definite proportions apply to elements or mixtures? Explain.
_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
5. State the four basic principles of Dalton’s atomic model.
a)
_____________________________________________________________________________
b)
_____________________________________________________________________________
c)
_____________________________________________________________________________
d)
_____________________________________________________________________________
6.
How did Dalton’s model account for the law of conservation of mass?
_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
7.
How did Dalton’s model account for the law of definite proportions?
_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
8.
Suppose a reaction occurs in which all reactants are completely consumed.
a)
How does the mass of the products compare with the mass of the reactants?
_____________________________________________________________________________
b)
Who first identified this relationship?
_____________________________________________________________________________
c)
What law explains this relationship?
_____________________________________________________________________________
9.
Consider the compound ammonia (NH3).
a)
Will samples of ammonia taken from different sources always contain the same
percentage, by mass, of nitrogen?
_____________________________________________________________________________
b)
What law explains this relationship?
_____________________________________________________________________________
c)
Who first identified this relationship?
_____________________________________________________________________________
10. What would Proust say about the composition of all samples of carbon dioxide
(CO2)?
_________________________________________________________________________________
_________________________________________________________________________________
11. What would Dalton say about the composition of all samples of carbon dioxide
(CO2)?
_________________________________________________________________________________
_________________________________________________________________________________
12. Explain the function of a scientific model.
_________________________________________________________________________________
_________________________________________________________________________________
13. On the line, write the word(s) that best complete(s) each statement.
a)
The negatively charged electrode of a cathode ray tube is the _________________.
b)
Rutherford’s experiment showed that the charge on the nucleus of the atom
must be _____________________.
c)
In his experiments with cathode ray tubes, Thomson concluded that cathode
rays were composed of particles that were _____________________ charged.
d)
A stream of particles originating from a cathode is called a(n) ________________.
e)
_____________________ discovered the canal ray.
f)
The negatively charged particle found outside the nucleus of the atoms is the
_____________________.
g)
The small core at the center of an atom containing a positive charge is the
_____________________.
h)
_____________________ is credited with performing the oil drop experiment.
i)
Millikan performed an experiment to measure the _____________________ of an
electron.
j)
_____________________ proposed the first atomic model that accounted for the
electrical nature of the atom.
k)
_____________________ proposed that an atom was an indivisible sphere.
l)
_____________________ developed the cathode ray tube.
m)
_____________________ discovered the electron.
n)
_____________________ proposed the existence of the nucleus of the atom.
o)
_____________________ was the first person to identify the neutron.
p)
The _____________________ was the first subatomic particle discovered.
q)
_____________________ used metallic foil as a target for alpha bombardment.
r)
Thomson determined the _____________________ for the electron and for the
proton.
s)
In his experiments with cathode ray tubes, Thomson showed that anode rays
were composed of particles that were _____________________ charged.
t)
_____________________ showed that each element has a unique number of
protons.