1. Chapter 4 Atomic Structure 4.1 Defining the Atom
4.2 Structure of the Nuclear Atom
4.3 Distinguishing Among Atoms
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2. Early Models of the Atom
Atom: smallest particle of an element that retains its identity in a chemical reaction.
Atomos – Greek word for indivisible
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3. It’s like an ID number for an element
Atomic Number
Atomic Number: number of protons in the nucleus of an atom
It’s like an ID number for an element

4. Atoms contain 3 types of subatomic particle
Key Concepts
Atoms contain 3 types of subatomic particle
Subatomic Particle
Symbol
Charge
Location
Proton p+ +1
nucleus
Neutron n0
Electron e- -1
surrounding nucleus
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5. Mass of Subatomic Particles Relative mass (mass of proton = 1)
Interpret Data
Mass of Subatomic Particles
Particle
Relative mass (mass of proton = 1)
Actual mass (g)
Proton
1 amu
1.67  10–24
Neutron
Electron
1/1840 amu
9.11  10–28
Atomic Mass Unit: 1/12 of the mass of a Carbon-12 atom
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6. Mass Number
Mass Number: total number of protons and neutrons in an atom Hyphenated notation: Helium-4

7. Atoms
If you know the atomic number and mass number, you can determine the atom’s composition. # Protons = Atomic Number # Electrons = # Protons (for a neutral atom) # Neutrons = Mass Number – Atomic Number

8. Determining the Composition of an Atom
Sample Problem 4.2
Determining the Composition of an Atom
How many protons, electrons, and neutrons are in each atom?
Protons:
Neutrons:
Electrons:
a. Be b. Ne c. Na 9 4 20 10 23 11
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9. Isotopes
Isotopes: atoms that have the same number of protons but different numbers of neutrons.
Neon-20, neon-21, and neon-22 are three isotopes of neon.
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10. Atomic Mass
Atomic mass - weighted average mass of atoms in a naturally occurring sample of the element.
reflects both mass & relative abundance
Atomic Mass
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11. If a student’s grade is weighted per the table below, what would their grade be?
Average
Tests
50% 79
Classwork
30% 95
Homework
20% 85

12. Most elements occur as a mixture of two or more isotopes.
Mass
(amu)
Relative Abundance
Magnesium-24
23.985
78.99%
Magnesium-25
24.986
10.00%
Magnesium-26
25.983
11.01%
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13. Interpret Data Natural Percent Abundance of
Stable Isotopes of Some Elements
Name
Symbol
Natural percent abundance
Mass (amu)
Atomic mass
Hydrogen H
99.985
0.015
negligible
1.0078
2.0141
3.0160
1.0079
Helium He
0.0001
4.0026
Carbon C
98.89
1.11
12.000
13.003
12.011
Oxygen O
99.759
0.037
0.204
15.995
16.995
17.999
15.999
Chlorine Cl
75.77
24.23
34.969
36.966
35.453 35 17 37 1 2 3 12 6 13 4 18 8 16
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14. Atomic Mass
To calculate atomic mass, multiply the mass of each isotope by its natural abundance, expressed as a decimal, and then add the products.
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15. Calculating Average Atomic Mass
Chlorine-35 has an amu of with an abundance of % while Chlorine-37 has an amu of and an abundance of %. What is the average atomic mass of chlorine?

16. Calculating Average Atomic Mass
Chlorine-35 has an amu of with an abundance of % while Chlorine-37 has an amu of and an abundance of %. What is the average atomic mass of chlorine? Carbon-12 (12.00 amu) makes up 98.93% of all of the carbon atoms, while carbon-13 ( amu) is about 1.07% abundant. What is the average atomic mass of carbon?

17. Calculating Average Atomic Mass
Chlorine-35 has an amu of with an abundance of % while Chlorine-37 has an amu of and an abundance of %. What is the average atomic mass of chlorine? Carbon-12 (12.00 amu) makes up 98.93% of all of the carbon atoms, while carbon-13 ( amu) is about 1.07% abundant. What is the average atomic mass of carbon?

18. Radioactivity: release of energy & matter that results from changes in the nucleus of an atom
All elements with an atomic number greater than 83 are radioisotopes (unstable nucleii)
Elements with atomic numbers less than or equal to 83 have isotopes with stable nucleii and may have a radioactive isotope

19. END OF CHAPTER 4
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