Isotopic Notation Chemistry 11

Definition of an Isotope Isotopes are atoms with the same number of protons but different number of neutrons Isotopes are atoms with the same number of protons but different number of neutrons

A Z X Z X A = mass number (the total number of protons + neutrons) (the total number of protons + neutrons) Z = atomic number (the total number of protons) (the total number of protons) X = element symbol

Understanding Isotopic Notation Sc 21 Sc 46 = mass number (the total number of protons ( 21 ) + neutrons ( 25 ) (the total number of protons ( 21 ) + neutrons ( 25 ) 21 = atomic number (the total number of protons ( 21 )) (the total number of protons ( 21 )) Sc = element symbol In a neutral atom, the number of electrons (21) is equal to the number of protons.

Practice these: 15 N # protons = ____ # neutrons= ____ # electrons = ___ # protons = ____ # neutrons= ____ # electrons = ___ 35 P # p + = ____ # n = ____ #e - = ___ # p + = ____ # n = ____ #e - = ___ 62 Cu 2+ # p + = ____ # n = ____ #e - = ___ # p + = ____ # n = ____ #e - = ___ 76 Se 3- # p + = ____ # n = ____ #e - = ___ # p + = ____ # n = ____ #e - = ___

Practice these 1.Write the symbol for the atom with an atomic number of 21 and a mass number of Give the complete chemical notation for the atom with 23 protons, 26 neutrons and 20 electrons. 3.Write the isotopic notation for a.Z = 46A = 110 b.An atom containing 24 protons, 28 neutrons, and 21 electrons c.Titanium Sc 49 V Pd 52 Cr Ti

Practice Problems Pt 4+ # p = _____# n = _____ # e- = _____ # p = _____# n = _____ # e- = _____ mass number = ________ atomic number = _______ mass number = ________ atomic number = _______ atomic mass = ________ name of element = _______ atomic mass = ________ name of element = _______ 2. Indicate the appropriate atomic mass of an element with 30 protons, 30 neutrons, and 28 electrons. protons, 30 neutrons, and 28 electrons amu platinum amu

Atomic Mass The atomic mass of an element represents the average mass of all the isotopes found in nature. The atomic mass of an element represents the average mass of all the isotopes found in nature. No element exists with only one possible isotope. No element exists with only one possible isotope. Hydrogen has the smallest number of isotopes: Hydrogen has the smallest number of isotopes: 1 H protium, 2 H deuterium, 3 H tritium. 1 H protium, 2 H deuterium, 3 H tritium.

Calculating Atomic Mass If you look at your periodic table, for hydrogen, the atomic mass is amu (atomic mass units). If you look at your periodic table, for hydrogen, the atomic mass is amu (atomic mass units). The atomic mass is calculated by adding the % of 1 H mass found in nature to the % of 2 H mass found in nature plus the % of 3 H mass. The atomic mass is calculated by adding the % of 1 H mass found in nature to the % of 2 H mass found in nature plus the % of 3 H mass. % 1 H + % 2 H + % 3 H = average mass (atomic mass) % 1 H + % 2 H + % 3 H = average mass (atomic mass) Generally the formula used is: Generally the formula used is: % X + % Y + % Z… = atomic mass. % X + % Y + % Z… = atomic mass.

Mass Spectrometer An instrument called the mass spectrometer is generally used to determine the percentages and individual masses of each isotope. An instrument called the mass spectrometer is generally used to determine the percentages and individual masses of each isotope.

Sample Problem Silver is found to have two stable isotopes, one has an atomic mass of amu and the other weighs amu. Silver is found to have two stable isotopes, one has an atomic mass of amu and the other weighs amu. The first isotope represents % of the mass of the element and the second represents %. The first isotope represents % of the mass of the element and the second represents %. What is the atomic mass of the element silver? What is the atomic mass of the element silver?

Solution The equation to use is: %X + % Y = average atomic mass And remember to convert your percentage amounts into fractions (by dividing by 100) before you begin anything!  (0.5182) amu + (0.4818) amu = mass amu amu = amu Now look at the periodic table to verify the answer.

Try This: A sample of neon contains three isotopes, neon-20 (with an isotopic mass of amu), neon-21 ( amu) and neon-22 ( amu). The natural abundances of these isotopes are 90.92%, %, and 8.82 %. Calculate the atomic weight of neon amu

Group Problems 1. The element with atomic number 53 contains: a)53 neutrons b)53 protons c)26 neutrons & 27 protons d)26 protons & 27 neutrons

2.The number of neutrons in an atom of 47 Ag is: a) 47 b) 108 c) 155 d) The number of electrons in an ion of 13 Al 3+ is: a) 13 b) 10 c) 27 d) 14