How is the structure of the atom related to its behavior?
Chemistry: Unit 3
Name:________________________
______/ 110pts
New Skills:
 Calculate weighted atomic masses
 Predict products of a nuclear reaction
 Calculate Half-life
3:1 Early ideas about Matter- The ancient Greeks tried to explain matter, but the scientific
study of the atom began with John Dalton in the early 1800’s.
1. (6pts) Compare and contrast the atomic models of Democritus, Aristotle and Dalton.
How are Democritus and Dalton’s theories similar? What were the two main ideas
behind Aristotle’s views?
2. (3pts) Understand how Dalton’s theory explains the conservation of mass. Which
one of John Dalton’s main ideas in his theory represents the idea of law of conservation
of mass?
a. (3pts) Which one of John Dalton’s main ideas in his theory represents the idea
of law of definite proportions?
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b. (4pts) Which of John Dalton’s main ideas in his theory are incorrect and why?
3:2 Defining the Atoms - An atom is made of a nucleus containing protons and neutrons;
electrons move around the nucleus.
1. (4pts) Define the atom.
2. (9pts) Distinguish between the subatomic particles in terms of relative charge and
mass. List the three main subatomic particles, their relative mass and their relative
charge.
3. (3pts) Describe the structure of the atom, including the locations of the subatomic
particles. Where are the locations of each of the three main subatomic particles?
a. (6pts) What three experiments led to the discovery of the electron, the
electron’s charge and mass, and the nucleus?
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3:3 How Atoms Differ -The number of protons and the mass number define the type of atom.
1. (3pts) Explain the role of atomic number in determining the identity of an atom.
2. (4pts) Define an isotope.
a. (3pts) What subatomic particles are the same in isotopes and what subatomic
particle is different?
3. (3pts) Explain why atomic masses are not whole numbers.
a. (5pts) Copper has two stable isotopes. Cu-63 has a mass of 62.93 amu and is
69.15% abundant. Cu-65 has a mass of 64.93 amu and is 30.85 % abundant.
What is the average atomic mass of copper? Show work.
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4. (5pts) Calculate the number of electrons, protons, and neutrons in an atom given its
mass number and atomic number. How many protons, neutrons and electrons are in
the following isotopes:
a. Mg-24
b. Sn-120
c. Ba-140
3:4 Unstable Nuclei and Radioactive Decay - Unstable atoms emit radiation to gain
stability.
1. (3pts) Explain the relationship between unstable nuclei and radioactive decay.
What is radioactive decay?
a. (4pts) What is a nuclear reaction?
b. (4pts) What relationship in the atom is the main reason for radioactive decay?
Give an example.
2. (15pts) Characterize alpha, beta, and gamma radiation in terms of mass and charge.
Define alpha, beta and gamma radiation and include its mass, charge and symbol.
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a. (9pts) What element would result from the following radioactive decay. Show
reactions and work.
i. The alpha decay of Po-21
ii. The beta decay of Pb-210
iii. The gamma decay of U-234
3. (3pts) Solve problems involving radioactive decay rates. What is the formula and
what do the variables represent when solving for half life?
a. (5pts) Krypton-85 is used in indicator lights of appliances. The half-life of
krypton-85 is 11years. How much of a 5.00 mg sample remains after 49 years?
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3:5 – Accumulating Content and Skills:– Chemistry content is continuous and builds on
prior knowledge and skills. This section will combine this unit with previous units.
Objective: Apply knowledge and skills from previous units to content learned in this unit.

(3pts) How does law of conservation of mass apply to nuclear reactions?

(3pts) How did the scientific method affect the history of chemistry?
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