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1 The Atom Atomic Number and Mass Number Isotopes

2 Atomic Theory Atoms are building blocks of elements Similar atoms in each element Different from atoms of other elements Two or more different atoms bond in simple ratios to form compounds

3 Subatomic Particles ParticleSymbol Charge Relative Mass Electron e - 1- 0 Proton p + + 1 Neutron n0 1

4 Location of Subatomic Particles 10 -13 cm electrons protons neutrons 10 -8 cm nucleus

Counts the number of protons in an atom 5 Atomic Number

6 Periodic Table Represents physical and chemical behavior of elements Arranges elements by increasing atomic number Repeats similar properties in columns known as chemical families or groups

1 2 3 4 5 6 7 8 7 Periodic Table 11 Na

8 Atomic Number on the Periodic Table 11 Na Atomic Number Symbol

9 All atoms of an element have the same number of protons 11 Na 11 protons Sodium

State the number of protons for atoms of each of the following: A. Nitrogen 1) 5 protons 2) 7 protons 3) 14 protons B. Sulfur 1) 32 protons 2) 16 protons 3) 6 protons C. Barium 1) 137 protons 2) 81 protons 3) 56 protons 10 Learning Check AT 1

State the number of protons for atoms of each of the following: A. Nitrogen 2) 7 protons B. Sulfur 2) 16 protons C. Barium 3) 56 protons 11 Solution AT 1

12 Number of Electrons An atom is neutral The net charge is zero Number of protons = Number of electrons Atomic number = Number of electrons

Counts the number of protons and neutrons in an atom 13 Mass Number

Show the mass number and atomic number Give the symbol of the element mass number 23 Na sodium-23 atomic number 11 14 Atomic Symbols

15 More Atomic Symbols 163165 O P Zn 81530 8 p + 15 p + 30 p + 8 n16 n35 n 8 e - 15 e - 30 e -

Atoms with the same number of protons, but different numbers of neutrons. Atoms of the same element (same atomic number) with different mass numbers Isotopes of chlorine 35 Cl 37 Cl17 chlorine - 35 chlorine - 37 16 Isotopes

Naturally occurring carbon consists of three isotopes, 12 C, 13 C, and 14 C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12 C 13 C 14 C 6 6 6 #P _______ _______ _______ #N _______ _______ _______ #E _______ _______ _______ 17 Learning Check AT 2

18 Solution AT 2 12 C 13 C 14 C 6 6 6 #P __6___ _ 6___ ___6___ #N __6___ _ _7___ ___8___ #E __6___ _ 6___ ___6___

An atom of zinc has a mass number of 65. A.Number of protons in the zinc atom 1) 302) 353) 65 B.Number of neutrons in the zinc atom 1) 302) 353) 65 C. What is the mass number of a zinc isotope with 37 neutrons? 1) 372) 653) 67 19 Learning Check AT 3

An atom of zinc has a mass number of 65. A.Number of protons in the zinc atom 1) 30 B.Number of neutrons in the zinc atom 2) 35 C. What is the mass number of a zinc isotope with 37 neutrons? 3) 67 20 Solution AT 3

21 Learning Check AT 4 Write the atomic symbols for atoms with the following: A. 8 p +, 8 n, 8 e - ___________ B.17p +, 20n, 17e - ___________ C. 47p +, 60 n, 47 e - ___________

16 O A. 8 p +, 8 n, 8 e - 8 B.17p +, 20n, 17e - 37 Cl 17 C. 47p +, 60 n, 47 e - 107 Ag 47 22 Solution AT 4

23 Learning Check AT 5 An atom has 14 protons and 20 neutrons. A.Its atomic number is 1) 142) 163) 34 B. Its mass number is 1) 142) 163) 34 C. The element is 1) Si2) Ca3) Se D.Another isotope of this element is 1) 34 X 2) 34 X 3) 36 X 16 14 14

An atom has 14 protons and 20 neutrons. A.It has atomic number 1) 14 B. It has a mass number of 3) 34 C. The element is 1) Si D.Another isotope of this element would be 3) 36 X 14 24 Solution AT 5

A scale designed for atoms gives their small atomic masses in atomic mass units (amu) An atom of 12 C was assigned an exact mass of 12.00 amu Relative masses of all other atoms was determined by comparing each to the mass of 12 C An atom twice as heavy has a mass of 24.00 amu. An atom half as heavy is 6.00 amu. 25 Masses of Atoms

26 Atomic Mass Listed on the periodic table Gives the mass of “average” atom of each element compared to 12 C Average atom based on all the isotopes and their abundance % Atomic mass is not a whole number Na 22.99

27 Learning Check AT6 Using the periodic table, specify the atomic mass of each element (round to the tenths place): A.calcium__________ B. aluminum__________ C. lead__________ D. barium__________ E. iron__________

28 Solution AT6 Using the periodic table, specify the atomic mass of each element (round to the tenths place): A.calcium_40.1 amu _ B. aluminum_27.0 amu _ C. lead_207.2 amu_ D. barium_137.3 amu_ E. iron_55.8 amu__

29 Calculating Atomic Mass Percent(%) abundance of isotopes Mass of each isotope of that element Weighted average = mass isotope 1 (%) + mass isotope 2 (%) + … 100 100

Isotopes Mass of Isotope Abundance 24 Mg =24.0 amu 78.70% 25 Mg = 25.0 amu 10.13% 26 Mg = 26.0 amu 11.17% Atomic mass (average mass) Mg = 24.3 amu 30 Atomic Mass of Magnesium Mg 24.3

Gallium is a metallic element found in small lasers used in compact disc players. In a sample of gallium, there is 60.2% of gallium-69 (68.9 amu) atoms and 39.8% of gallium-71 (70.9 amu) atoms. What is the atomic mass of gallium ? 31 Learning Check AT7

32 Solution AT7 Ga-69 68.9 amu x 60.2 = 41.5 amu for 69 Ga 100 Ga-71 (%/100) 70.9 amu x 39.8 = 28.2 amu for 71 Ga 100 Atomic mass Ga = 69.7 amu

33 Finding An Isotopic Mass A sample of boron consists of 10 B (mass 10.0 amu) and 11 B (mass 11.0 amu). If the average atomic mass of B is 10.8 amu, what is the % abundance of each boron isotope?

34 Assign X and Y values: X = % 10 B Y = % 11 B Determine Y in terms of X X + Y = 100 Y = 100 - X Solve for X: X (10.0) + (100 - X )(11.0) = 10.8 100 100 Multiply through by 100 10.0 X + 1100 - 11.0X = 1080

35 Collect X terms 10.0 X - 11.0 X = 1080 - 1100 - 1.0 X = -20 X = -20 = 20 % 10 B - 1.0 Y = 100 - X % 11 B = 100 - 20% = 80% 11 B

36 Learning Check AT8 Copper has two isotopes 63 Cu (62.9 amu) and 65 Cu (64.9 amu). What is the % abundance of each isotope? (Hint: Check periodic table for atomic mass) 1) 30%2) 70%3) 100%

37 Solution AT8 2) 70% Solution 62.9X + 6490 = 64.9X = 6350 -2.0 X = -140 X = 70%

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