1. Chapter 3 Atoms and Elements

2. Classification of Matter

3. Elements
Elements are
Pure substances that cannot be separated into simpler substances by ordinary laboratory processes
The building blocks of matter
gold (Au) carbon (C) aluminum (Al)
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**Memorize the symbols of the first 36 elements!!

4. Periodic Table Copyright © 2005 by Pearson Education, Inc.
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5. Groups and Periods Copyright © 2005 by Pearson Education, Inc.
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6. Names of Some Representative Elements
Several groups of representative elements are known by common names.
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7. Identify the element described by the following:
A. Group 7A(17), Period 4
1) Br 2) Cl 3) Mn
B. Group 2A(2), Period 3
1) beryllium 2) magnesium 3) boron
C. Group 5A(15), Period 2
1) phosphorus 2) arsenic 3) nitrogen

8. Solution A. Group 7A, Period 4 1) Br B. Group 2A, Period 3
2) magnesium
C. Group 5A(15), Period 2
3) nitrogen

9. Metals, Nonmetals, and Metalloids
The heavy zigzag line
separates metals and
nonmetals.
Metals are located to the left.
Nonmetals are located to the right.
Metalloids are located along the heavy zigzag line between the metals and nonmetals.
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10. Comparing a Metal, Metalloid, and Nonmetal

11. Dalton’s Atomic Theory
Matter is composed of tiny particles called atoms.
Atoms of each element are similar, and different from atoms of other elements.
Atoms of two or more different elements combine to form compounds.
A chemical reaction involves changes in the arrangement or combination of atoms.
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12. Rutherford’s Gold-Foil Experiment
Positively charged particles were aimed at atoms of gold
Most went straight through the atoms
Only a few were deflected
Conclusion: There must be a small, dense, positively charged
nucleus in the atom that deflects positive particles that come close.
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13. Structure of the Atom An atom consists
Of a nucleus that contains protons and neutrons
Of electrons in a large empty space around the nucleus
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14. Particles in the Atom

15. Atomic Number 11 Na Atomic Number Symbol The atomic number
Is specific for each element (DEFINES an element)
Is the same for all atoms of an element
Is equal to the number of protons in an atom
Appears above the symbol of an element 11 Na
Atomic Number
Symbol

16. State the number of protons in each:
A. A nitrogen atom
1) 5 protons 2) 7 protons ) 14 protons
B. A sulfur atom
1) 32 protons 2) 16 protons ) 6 protons
C. A barium atom
1) 137 protons ) 81 protons ) 56 protons

17. Solution State the number of protons in each: A. A nitrogen atom
2) atomic number 7; 7 protons
B. A sulfur atom
2) atomic number 16; 16 protons
C. A barium atom,
3) atomic number 56; 56 protons

18. Electrons in an Atom
An atom of any element is electrically neutral; the net charge of an atom is zero.
In an atom, the number of protons is equal to the number of electrons.
number of protons = number of electrons
For example, an atom of aluminum has 13 protons and 13 electrons. The net charge is zero.
13 protons (13 +) electrons (13 -) = 0

19. Mass Number The mass number
Represents the number of particles in the nucleus
Is equal to the
Number of protons + Number of neutrons

20. An atom of zinc has a mass number of 65.
A. How many protons are in this zinc atom?
1) ) ) 65
B. How many neutrons are in the zinc atom?
C. What is the mass number of a zinc atom that has
37 neutrons?
1) ) ) 67

21. Solution An atom of zinc has a mass number of 65.
A. How many protons are in this zinc atom?
1) 30 (atomic number 30)
B. How many neutrons are in the zinc atom?
2) 35 (65 – 30 = 35)
C. What is the mass number of a zinc atom that has 37 neutrons?
3) 67 ( = 67)

22. An atom has 14 protons and 20 neutrons.
A. Its atomic number is
1) ) ) 34
B. Its mass number is
C. The element is
1) Si 2) Ca 3) Se

23. Solution An atom has 14 protons and 20 neutrons.
A. Its atomic number is
1) 14
B. It has a mass number of
3) 34 ( = 34)
C. The element is
1) Si (Atomic number 14)

24. Nuclear Symbols
From the nuclear symbol, we can determine the number of protons (p+), neutrons, (n), and electrons (e-) in a particular atom.
O P Zn
8 p+ 15 p p+
8 n 16 n 35 n
8 e- 15 e e-
Mass number
Atomic number

25. Isotopes
Isotopes
Are atoms of the same element that have different mass numbers
Have the same number of protons, but different numbers of neutrons

26. Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of the following:
12C 13C 14C
protons ______ ______ ______
neutrons ______ ______ ______
electrons ______ ______ ______

27. Solution
Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of the following:
12C 13C 14C
protons 6 p+ 6 p p+
neutrons 6 n 7 n 8 n
electrons 6 e- 6 e- 6 e-

28. Write the nuclear symbols for atoms with the following subatomic particles:
A. 8 p+, 8 n, 8 e- ___________
B. 17p+, 20n, 17e- ___________
C. 47p+, 60 n, 47 e- ___________

29. Solution
Write the nuclear symbols for atoms with the following subatomic particles:
16O
A. 8 p+, 8 n, 8 e
B. 17p+, 20 n, 17e- 37Cl 17
C. 47p+, 60 n, 47 e- 107Ag 47

30. Atomic Mass Na 22.99 The atomic mass of an element
Is listed below the symbol of each element on the periodic table
Gives the mass of an “average” atom of each element compared to 12C
Is not the same as the mass number Na
22.99

31. Atomic Mass for Cl
The atomic mass of chlorine is the weighted average of two isotopes 35Cl and 37Cl.
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32. Calculating Atomic Mass for Cl
35Cl has atomic mass (75.78%) and 37C has
atomic mass (24.22%).
The atomic mass and percent of each isotope are used to calculate the contribution of each isotope to the weighted average.
x = amu
100
x = amu
amu
The sum is the weighted average or atomic mass Cl = amu

33. Examples of Isotopes and Atomic Masses
Most elements have two or more isotopes that contribute to the atomic mass of that element.

34. Gallium is an element found in small lasers used in compact disc players. In a sample of gallium, there is 60.11% of 69Ga (atomic mass 68.93) atoms and 39.89% of 71Ga (atomic mass 70.93) atoms.
What is the atomic mass of gallium?

35. Solution 69Ga 68.93 amu x 60.11 = 41.43 amu (from 69Ga) 100 71Ga
Atomic mass Ga = amu 31 Ga
69.72