2 IsotopesIsotopesare atoms of the same element that have different mass numbers.have the same number of protons, but different numbers of neutrons.
3 Atomic Symbol An atomic symbol represents a particular atom of an element.gives the mass number in the upper left corner and the atomic number in the lower left corner.Example: An atom of sodium with atomic number 11 and a mass number 23 has the following atomic symbol:mass number 23Naatomic number
4 Information from Atomic Symbols The atomic symbol for a specific atom of an elementgives thenumber of protons (p+),number of neutrons (n),and number of electrons (e-).4
5 Information from Atomic Symbols Examples of number of subatomic particles for atomsAtomic symbolO P Zn8 p+ 15 p p+8 n 16 n n8 e- 15 e e-
6 Learning CheckNaturally 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 14Cprotons ______ ______ ______neutrons ______ ______ ______electrons ______ ______ ______
7 Solution 12C 13C 14C 6 6 6 protons 6 p+ 6 p+ 6 p+ neutrons 6 n 7 n 8 n protons 6 p+ 6 p p+neutrons 6 n 7 n 8 nelectrons 6 e- 6 e- 6 e-
8 Learning CheckWrite the atomic 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- ___________
9 Solution A. 8 p+, 8 n, 8 e- 16O 8 B. 17p+, 20 n, 17e- 37Cl 17 C. 47p+, 60 n, 47 e- 107Ag47
10 Learning Check 1. Which of the pairs are isotopes of the same element? 2. In which of the pairs do both atoms have 8 neutrons?A. 15X 15XB. 12X 14XC. 15X 16X
11 SolutionB. 12X 14XThe atomic symbols in “B.” represent isotopes of carbon with 6 protons each, but one has 6 neutrons and the other has 8.C. 15X 16XThese isotopes of nitrogen and oxygen have 8 neutrons.
15 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.Na22.99
16 Isotopes of Some Elements and Their Atomic Mass Most elements have two or more isotopes that contribute to the atomic mass of that element.
17 Atomic Mass for Cl The atomic mass of chlorine is due to all the Cl isotopes.not a whole number.the average of two isotopes: 35Cl and 37Cl.
18 Learning Check Using the periodic table, specify the atomic mass of each element.A. calcium __________B. aluminum __________C. lead __________D. barium __________E. iron __________
19 Solution Using the periodic table, specify the atomic mass of each element:A. calcium amuB. aluminum amuC. lead amuD. barium amuE. iron amu
20 Calculating Atomic Mass The calculation for atomic mass requires thepercent(%) abundance of each isotope.atomic mass of each isotope of that element.sum of the weighted averages.mass of isotope(1)x (%) + mass of isotope(2) x (%) +
21 Calculating Atomic Mass for Cl 35Cl has atomic mass amu (75.76%) and 37Chas atomic mass amu (24.24%).Use atomic mass and percent of each isotope to calculate the contribution of each isotope to the weighted average.x = amu100x = amuSum is atomic mass of Cl amu
22 Calculating Atomic Mass Mg Isotope Mass Abundance24Mg = amu x /100 = amu25Mg = amu x /100 = amu26Mg = amu x /100 = amuAtomic mass (average mass) Mg = amu
23 Atomic Mass of Magnesium The atomic mass of Mgis due to all the Mg isotopes.is a weighted average.is not a whole number.
24 Learning CheckGallium is an element found in lasers used in compact disc players. In a sample of gallium, there is 60.10% of 69Ga (atomic mass ) atoms and 39.90% of 71Ga (atomic mass ) atoms.What is the atomic mass of gallium?
25 Solution 69Ga 68.926 amu x 60.10 = 41.42 amu (from 69Ga) 100 71Ga Atomic mass Ga = amu31Ga69.72