Ch 3_handouts - 1 3.1 Atomic Masses 3.2 The Mole 3.3 Molar...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 1 3.1 Atomic Masses 3.2 The Mole 3.3 Molar Mass 3.4 Percent Composition of Compounds 3.5 Determining the Formula of a Compound 3.6 Chemical Equations 3.7 Balancing Chemical equations 3.8 Stoichiometric Calculations: Amounts of Reactants and Products 3.9 Calculations Involving a Limiting Reactant Chapter 3 Stoichiometry Mole - Mass Relationships in Chemical Systems 2 Atomic Mass Unit (amu) = 1/12 the mass of a carbon-12 atom; on this scale hydrogen has a mass of 1.008 amu (unied atomic mass unit...u) Dalton (D) = another name for the atomic mass unit; on this scale 12 C has a mass of 12.00 Daltons;1 Dalton = 1 amu Isotopic Mass = The relative mass of an isotope compared to the 12 C isotope standard = 12.00 amu Atomic Mass or Atomic Weight of an element = the average of the masses of its naturally occurring isotopes weighted according to their abundances. Atomic Defnitions 3 GRAVIMETRY weighing and analyzing an element or compound MASS SPECTROMETRY ionization of elements and defection of their path by applied magnetic Feld; RATIO oF atomic masses determined; accurate comparison of masses of elements and their isotopes. How Do We Determine Atomic Mass? 4 5 3.1) Operation of a Mass Spectrometer A B C D E A. Sample vaporized (made into a gas) B. Electron gun removes an electron, forming a positively charged species C. Positive ion accelerated through an electric Feld D. Magnetic deection Lighter ions deected more than heavier ones. E. Observe impact on detector 6 igure 3.2b: Relative peak areas 91% 20 Ne 0.3% 21 Ne 9% 22 Ne This gives the isotopic composition of Ne. igure 3.2a: Peaks of neon from injected sample THREE PEAKS, so THREE ISOTOPES! 7 What is the average atomic mass of the three stable isotopes of neon: 20 Ne ( 90.70%), 21 Ne (0.30%), and 22 Ne (9.00%)? 1. 20 amu 2. 20.2 amu 3. 21 amu 4. 21.1 amu 5. 22 amu 8 24 Mg (78.7%) 23.98504 amu x 0.787 = 18.876226 amu 25 Mg (10.2%) 24.98584 amu x 0.102 = 2.548556 amu 26 Mg (11.1%) 25.98636 amu x 0.111 = 2.884486 amu Total = 24.309268 amu Problem: Calculate the average atomic mass of the three stable isotopes of magnesium: 24 Mg ( 78.7%), 25 Mg (10.2%), and 26 Mg (11.1%). With appropriate signiFcant digits 24.3 amu 24 Mg (78.7%) 23.98504 amu 25 Mg (10.2%) 24.98584 amu 26 Mg (11.1%) 25.98636 amu Calculating the Average Atomic Mass of an Element 9 What is the abundance of the two bromine isotopes, 79 Br = 78.918336 amu and 81 Br = 80.91629 amu, given that the average mass of bromine is 79.904 amu? 1. 79 Br = 50.664% , 81 Br = 49.334% 2. 79 Br = 50.67% , 81 Br = 49.33% 3. 79 Br = 50.7% , 81 Br = 49.3% 10 Problem: Calculate the abundance of the two bromine isotopes, 79 Br = 78.918336 amu and 81 Br = 80.91629 amu, given that the average mass of bromine is 79.904 amu....
View Full Document

Page1 / 52

Ch 3_handouts - 1 3.1 Atomic Masses 3.2 The Mole 3.3 Molar...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online