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ATOMIC STRUCTURE: Chapter 4 Atoms and Elements
Topics:
Atomic Composition
Isotopes-Nuclide Symbols
Calculating Atomic Mass
Calculating Percent Composition
Valence Electrons
Ion names and Symbols
Standards Addressed:
Atomic and Molecular Structure
1a. Students know how to relate the position of an element in the periodic table to its atomic
number and atomic mass.
1b. Students know how to use the periodic table to identify metals, semi-metals {metalloids},
non-metals, and halogens
1e. Students know the nucleus of the atom is much smaller than the atom yet contains most
of its mass.
Anticipatory Set:
 What are atoms made up of?
 Where do you find these particles?
Objectives:
By the end of the lesson, the student will:
 Know the 3 particles of the atom and where they reside
 Know the difference between atomic number and mass number
 Know how to write nuclide symbols
 Know the three isotopes of hydrogen
 Know how to calculate atomic mass
 Know how to calculate percent composition
 Know how to determine the number of valence electrons
 Know how to write ion names and symbols
Purpose: Reason doing lesson. Future purpose. Big picture.
 We will use this information to build our chemistry knowledge.
 We will use this information as the foundation to calculate limiting reagent
problems.
 The standardized exams in the spring will test you on this information.
Teacher Input
Vocab:
Atom- from the Greek atomos=indivisible
The atom is the smallest particle of an element that retains the properties of that
element.
Nucleus: the center of the atom; composed of neutrons and protons. Because the
mass of the proton and the neutron is much larger than that of electrons, almost all
the mass is located in the nucleus.
Ion: a charged particle: anion and cation
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Protons:
Neutrons:
Electrons
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
Qt: What differentiates one atom from another atom?
Atomic Number (Z):






(CFU)
Qt.
What does it mean to be electrically neutral?
Qt: What observations can you make about atomic numbers on the periodic table?
(CFU & GP)
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

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What is the atomic number of Chlorine?
What can you tell me about its protons and electrons?
What element has 20 protons?
What is the relationship between the # protons and the atomic number?
Complete the chart:
Element
Symbol
Potassium
(GP)
Atomic Number
# Protons
5
16
Y
Qt. What accounts for the mass of the atom?
2
Mass Number (A):



Qt: What do the atomic number and the mass number have in common?
To find # neutrons:
1.
OR to find mass number:
2.
Complete the Chart:
Mass # # Protons
(GP)
Atomic #
9
14
# Neutrons # Electrons Chemical
Symbol
10
15
47
55
Nuclide
Symbol
22
25
6
C
Isotopes:




Nuclide Symbol:
Nuclide
A El
Z
A= mass number



3
Z= atomic number
Nuclide Name
# protons
Chemical Symbol C
# neutrons
[6, 7, 8]
# electrons
Nuclide Symbol
7
(CFU & GP)
Now write the nuclide symbol for the elements in the previous table.
3 Isotopes of Hydrogen
Isotope
Nuclide
of Hydrogen
Symbol
Protium
# protons
# neutrons
# electrons
1
0
1
Deuterium
1
1
1
Tritium
1
2
1
If you specify the nuclear structure, then you call it a nuclide. But if you say Carbon atom, you
do not know which Carbon atom it is, therefore you don’t know how many neutrons it has
Example: brothers and sisters-you are members of the Jones family, but you have not specified
which Jones member you are referring to. Jimmy Jones ~ 136C
(CFU & GP)
Write the nuclide name and nuclide symbol
# protons
# neutrons
# electrons Nuclide
Name
17
20
18
20
20
18
92
146
92
Nuclide
Symbol
Atomic Mass:


If you have a recipe, you could count items to put in, say 200 chocolate chips, 3 eggs, etc.
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But suppose I have a recipe to make a compound. I need 100 hydrogen atoms and 50 oxygen
atoms-you cannot count atoms or pluck them out with atomic tweezers!
So instead they mass them(weigh them)
Qt. What accounts for the mass of the atom?




Know that 1.0 amu is defined as exactly 1/12 the mass of a 126C atom.
Carbon-12 has 6 protons and 6 neutrons, therefore 1 proton or 1 neutron =
Know that 1 amu = 1.6606 x 10 -24 grams
Since the mass mostly depends on # protons and # neutrons, you’d think atomic mass
would be a whole number, but it isn’t. How come?

In nature,

Relative abundance-

Sample of carbon from anywhere in the world; coal from S. Africa or W. Virginia, or
Pennsylvania → 99% C-12 and 1% C-13

Atomic Mass of periodic table

→ Idea of weighted average
To Calculate Atomic Mass of an Element
To calculate atomic mass you need to know 3 things:
1.
2.
3.
Calculating atomic mass
For each isotope of the element:
mass of isotope X relative abundance + mass of isotope X relative abundance….=_______amu
Example: Chlorine Calculation
Isotope
Mass of Isotope
Cl-35
34.969
Cl-37
36.935
Relative Abundance
75.77%
24.23%
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Atomic Mass of Cl
Oh look, that’s the same value on the periodic table
(CFU & GP)
How many chlorine atoms actually have a mass of 35.45 amu?
So the atomic mass, in amu, is the average of a fictitious non-existent atom of an element.
Example: Copper Calculation
Isotope
Mass of Isotope
Cu-63
62.9298amu
Cu-65
64.9278
Calculation:
Relative Abundance
69.09%
30.91%
Atomic Mass
Suppose you are given the mass of the isotopes and the atomic mass of the element and you are
asked to calculate the relative abundance of each isotope
To Calculate % Abundance:
1.
2.
3.
4.
5.
Isotope
B-10
B-11
Mass of Isotope
10.013
11.009
Relative Abundance Atomic Mass
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