1. How many types of dogs are there?
CHEMISTRY & YOU
How many types of dogs are there?
Why are there so many different types?
How can there be different varieties of atoms?
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

2. Objectives: I will be able to:
explain what makes elements and isotopes different from each other.
calculate the number of neutrons in an atom.
calculate the atomic mass of an element.
explain why chemists use the Periodic Table.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

3. Atomic Number What makes one element different from another?
Elements are different because they contain different numbers of protons.
An element’s atomic number is the number of protons in the nucleus of an atom of that element.
The atomic number identifies an element.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

4. Atoms of the First Ten Elements
Interpret Data
For each element listed in the table below, the number of protons equals the number of electrons.
Atoms of the First Ten Elements
Name
Symbol
Atomic number
Protons
Neutrons
Mass number
Electrons
Hydrogen H 1
Helium He 2 4
Lithium Li 3 7
Beryllium Be 5 9
Boron B 6 11
Carbon C 12
Nitrogen N 14
Oxygen O 8 16
Fluorine F 10 19
Neon Ne 20
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

5. Remember that atoms are electrically neutral.
Atomic Number
Remember that atoms are electrically neutral.
Thus, the number of electrons (negatively charged particles) must equal the number of protons (positively charged particles).
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

6. Understanding Atomic Number
Sample Problem 4.1
Understanding Atomic Number
The element nitrogen (N) has an atomic number of 7. How many protons and electrons are in a neutral nitrogen atom?
Analyze Identify the relevant concepts.
The atomic number gives the number of protons, which in a neutral atom equals the number of electrons.
Solve Apply the concepts to this problem.
Identify the atomic number.
Then use the atomic number to find the number of protons and electrons.
A neutral nitrogen atom has 7 protons and 7 electrons.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

7. Number of neutrons = mass number – atomic number
mass number: the total number of protons plus neutrons in an atom
If you know the atomic number and mass number of an atom of any element, you can determine the atom’s composition.
The number of neutrons in an atom is the difference between the mass number and atomic number.
Number of neutrons = mass number – atomic number
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

8. Atomic Number and Mass Number
The composition of any atom can be represented in shorthand notation using atomic number and mass number.
The atomic number is the subscript.
The mass number is the superscript.
You can also refer to atoms by using the mass number and the name of the element.
Au may be written as gold-197.
Au is the chemical symbol for gold.
197 79
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

9. https://www. youtube. com/watch
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

10.  How many protons, electrons, and neutrons are in each atom? a. Be
b. Ne
c. Na
d.) What information is needed to determine the composition of a neutral atom of any element? 9 4 20 10 23 11
a.) 4, 4, 5
b.) 10, 10, 10
c.) 11, 11, 12
d.) atomic number and mass number
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

11. Isotopes How do isotopes of an element differ?
isotopes: atoms having the same atomic number (the same number of protons), but having different atomic masses due to different numbers of neutrons
There are three different kinds of neon atoms.
How do these atoms differ?
They all have the same number of protons and electrons but different numbers of neutrons.
Neon-20, neon-21, and neon 22 are three isotopes of neon.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

12. Isotopes
Because isotopes of an element have different numbers of neutrons, they also have different mass numbers.
Despite these differences, isotopes are chemically alike because they have identical numbers of protons and electrons, which are the subatomic particles responsible for chemical behavior.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

13. Remember the dogs at the beginning of the lesson.
Isotopes
Remember the dogs at the beginning of the lesson.
Their color or size doesn’t change the fact that they are all dogs.
Similarly, the number of neutrons in isotopes of an element does not change which element it is because the atomic number does not change.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

14. 
How are the atoms of one element different from the atoms of another element?
How are isotopes of the same element different?
Two stable isotopes of carbon are carbon-12 and carbon-13. What is the shorthand notation for each isotope using superscripts and subscripts to represent the mass number and the atomic number.
Different elements have different numbers of protons
Different isotopes have different numbers of neutrons and mass numbers
12/6C and 13/6C
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

15. 
Why are atoms with different numbers of neutrons still considered to be the same element?
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

16. Atomic Mass
atomic mass: the weighted average mass of the naturally occurring isotopes of an element
A weighted average mass reflects both the mass and the relative abundance of the isotopes as they occur in nature.
How do you calculate the atomic mass of an element?
The mass of even the largest atom is incredibly small.
Since the 1920s, it has been possible to determine the tiny masses of atoms by using a mass spectrometer.
The mass of a fluorine atom was found to be x 10–23 g.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

17. Atomic Mass
Data about the actual masses of individual atoms is useful information for areas of chemistry such as physical chemistry, but these values are inconveniently small and impractical to work with.
Instead, we compare the relative masses of atoms using a reference isotope as our standard value.
This reference isotope is carbon-12.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

18. Atomic Mass
The isotope of carbon-12 has been assigned a mass of exactly 12 atomic mass units (6 protons + 6 neutrons).
atomic mass unit (amu): a unit of mass, equal to 1/12 the mass of the carbon-12 atom and used to express the mass of atomic and subatomic particles
In nature, most elements occur as a mixture of two or more isotopes.
Each isotope of an element has a fixed mass and a natural percent abundance.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

19. 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
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

20. Atomic Mass
Chlorine occurs as two isotopes: chlorine-35 and chlorine-37.
If you calculate the arithmetic mean of these two masses (( amu amu)/2), you get an average atomic mass of
However, this value is higher than the actual value of
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

21. Atomic Mass
To explain this difference, you need to know the natural percent abundance of the isotopes of chlorine.
Chlorine-35 accounts for 76 percent of the naturally occurring chlorine atoms; chlorine-37 accounts for only 24 percent.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

22. Atomic Mass
Because there is more chlorine-35 than chlorine-37 in nature, the atomic mass of chlorine, amu, is closer to 35 than to 37.
Weighting the masses of the two isotopes is done through multiplying each isotope by its natural percent abundance:
(( x ) + ( x ))/2 =
A weighted average mass reflects both the mass and the relative abundance of the isotopes as they occur in nature.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

23.  The atomic mass of copper is 63.546 amu.
Which of copper’s two isotopes is more abundant: copper-63 or copper-65?
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

24. Atomic Mass You can determine atomic mass based on relative abundance.
To do this, you must know three things:
the number of stable isotopes of the element (radioactive isotopes are not used if their half-life is less than 1 x 1010 years (only thorium, protactinium, and uranium qualify)),
the mass of each isotope, and
the natural percent abundance of each isotope.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

25. Atomic Mass To calculate the atomic mass of an element:
Multiply the mass of each isotope by its natural abundance, expressed as a decimal, and then add the products of each together.
Carbon has two stable isotopes: carbon-12 and carbon-13.
Atomic mass of carbon = mass x relative abundance
( amu x ) + ( amu x )
= ( amu) + (0.144 amu)
= amu
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

26.  Element X has two naturally occurring isotopes.
Isotope A with a mass of amu has a relative abundance of percent.
Isotope B with a mass of amu has a relative abundance of percent.
In your notes, calculate the atomic mass of element X.
Atomic mass of element X = amu amu
= amu
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

27. Electrons and the Structure of Atoms
BIG IDEA
Electrons and the Structure of Atoms
Atoms of the same element have the same number of protons, which is equal to an atom’s atomic number.
But atoms of the same element can have different numbers of neutrons.
Atoms of the same element with different numbers of neutrons are isotopes.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

28.  Review
Why is the atomic mass of an element usually not a whole number?
What makes elements different from each other?
Isotopes differ from each other in two ways. What are they?
How do we calculate relative atomic mass?
How do we determine the number of neutrons in an isotope?
How do we know the number of electrons in a neutral charge atom?
because it is a weighted average of the masses of the naturally occurring isotopes
because they contain different numbers of protons
Number of neutrons and mass number
multiply the mass of each isotope by its natural abundance and then add the products
mass number – atomic number
Number of electrons = number of protons
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.