Name ___________________________________________________________ Date __________________
The Structure of the Atom
Section 3 How Atoms Differ
Skim Section 3 of your text. Focus on the headings, boldfaced words, and
main ideas. Then summarize the main ideas of this section.
1. _____________________________________________________
2. _____________________________________________________
3. _____________________________________________________
In the left margin, write the term defined below.
___________________
the number of protons in an atom
___________________
atoms with the same number of protons but different numbers of neutrons
___________________
the sum of the number of protons and neutrons in the nucleus
___________________
1/12 the mass of a carbon-12 atom; the standard unit of measurement for
the mass of atoms
___________________
the weighted average mass of the isotopes of an element
Define the following term.
specific
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Name ___________________________________________________________ Date __________________
Section 3 How Atoms Differ (continued)
Atomic Number
Use with page 115.
Explain how to use an atomic number to identify an element by
completing the paragraph below.
Each _________ of an element has a unique number of __________. Since
the overall charge of an atom is _________ the number of _________ equals
the number of _________. Atomic number = number of ________ = number
of ___________. If you know how many one of the three an atom contains,
you also know the other _________. Once you know the _______________,
the ________________ can be used to find the name of the _____________.
Atomic Number
Solve Read Example Problem 1 in your text.
Use with Example
Problem 1, page 116.
You Try It
Problem
Given the following information about atoms, determine the name of each
atom’s element and its atomic number.
a. Atom 1 has 11 protons
b. Atom 2 has 20 electrons
1. Analyze the Problem
Apply the relationship among atomic number, number of protons, and
number of electrons to determine the name and atomic number of each
element.
2. Solve for the Unknown
a. Atom 1
Atomic number = number of protons = number of electrons
Atomic number = ________ = number of electrons
The element with an atomic number of 11 is _______________
b. Atom 2
Atomic number = number of protons = number of electrons
Atomic number = number of protons = ______
The element with an atomic number of __________ is _____________.
3. Evaluate the Answer
The answers agree with ____________________ and element
___________________________ given in the periodic table.
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Name ___________________________________________________________ Date __________________
Section 3 How Atoms Differ (continued)
Isotopes and
Mass Number
Use with page 117.
Review your understanding of isotopes and mass number by completing
the following paragraph.
Isotopes are elements with ______________________________ but with
_______________________________. The number of neutrons can be
determined by _________________ the atomic number from the
____________________ . The mass number is
_________________________________________________________ .
Use Atomic
Number and
Mass Number
Use with Example
Problem 2, page 118.
Solve Read Example Problem 2 in your text.
You Try It
Problem
You are given two samples of carbon. The first sample, carbon-12, has a
mass number of 12, the second sample, carbon-13, has a mass number
of 13. Both samples have an atomic number of 6. Determine the
number of protons, electrons, and neutrons in each sample.
1. Analyze the Problem
Known:
Carbon-12
Carbon-13
Mass number is _______
Mass number is _______
Atomic number is ______
Atomic number is ______
Unknown:
The number of protons, electrons, and neutrons in each sample.
2. Solve for the Unknown
Number of protons = number of electrons = atomic number = _____
Number of neutrons = mass number − atomic number
The number of neutrons for carbon-12 = 12 − 6 = _______
The number of neutrons for carbon-13 = 13 − 6 = _______
3. Evaluate the Answer
The number of neutrons does equal the __________________ minus
the _________________, or the number of protons.
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Name ___________________________________________________________ Date __________________
Section 3 How Atoms Differ (continued)
Mass of Atoms
Use with pages 119–120.
Explain why the mass number for chlorine is more than 35.
________________________________________________________
________________________________________________________
________________________________________________________
Calculate
Atomic Mass
Use with Example
Problem 3, page 121.
Summarize Fill in the blanks to help you take notes while you read
Example Problem 3.
Problem
Given the __________ in the table in the left margin, ____________ the
______________ of unknown element X. Then, _________ the unknown
Isotope Abundance for
Element X
Isotope
6
7
Mass
Percent
(amu) abundance
X
6.015
7.59%
X
7.016
92.41%
________, which is used __________ to treat some _________________.
1. Analyze the problem
Known:
Unknown:
For isotope 6X:
_________________ of X = ? amu
mass = _________________
___________ of element X = ?
abundance = ____________________
For isotope 7X:
mass = ________________
abundance = ____________________
2. Solve for the unknown
Mass contribution = (________) (_____________________________)
For 6X: Mass contribution = ____________________ = ___________
For 7X: Mass contribution = ____________________ = __________
Sum the mass contributions to find the atomic mass.
_____________ of X = _________________________ = __________
Use the ____________________ to identify the element.
The element with an atomic mass of 6.939 amu is __________.
3. Evaluate the answer
The number of neutrons does equal the ________________ minus the
______________________, or number of ____________.
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