The Atom Atomic Number Mass Number Isotopes

Transcription

1 The Atom Atomic Number Mass Number Isotopes 1

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 2

3 Subatomic Particles Particle Symbol Charge Relative Mass Electron e Proton p Neutron n 0 1 3

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

5 Atomic Number Counts the number of protons in an atom 5

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 6

7 Periodic Table Na 7

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

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

10 Learning Check AT 1 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

11 Solution 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

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

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

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

15 More Atomic Symbols O P Zn p + 15 p + 30 p + 8 n 16 n 35 n 8 e - 15 e - 30 e - 15

16 Isotopes 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 Cl chlorine - 35 chlorine

17 Learning Check AT 2 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 #P #N #E 17

18 Solution AT 2 12 C 13 C 14 C #P #N 6 _7 8 #E

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 2) 35 3) 65 B. Number of neutrons in the zinc atom 1) 30 2) 35 3) 65 C. What is the mass number of a zinc isotope with 37 neutrons? 1) 37 2) 65 3) 67 19

20 Solution 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

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 - 21

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

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

24 Solution AT 5 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) 36X 14 24

25 Masses of Atoms 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 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 amu. An atom half as heavy is 6.00 amu. 25

26 Atomic Mass Na 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 26

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 27

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 28

29 Calculating Atomic Mass Percent(%) abundance of isotopes Mass of each isotope of that element Weighted average = mass isotope1(%) + mass isotope2(%)

30 Atomic Mass of Magnesium 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 Mg

31 Learning Check AT7 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

32 Solution AT7 Ga 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 32

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? 33

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

35 Collect X terms 10.0 X X = X = -20 X = -20 = 20 % 10 B Y = X % 11 B = % = 80% 11 B 35

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% 36

37 Solution AT8 2) 70% Solution 62.9X = 64.9X = X = -140 X = 70% 37