Name: Period: Date: KIPP NYC College Prep General Chemistry UNIT 2: Atomic Concepts Lesson 9: Calculating Average Atomic Mass By the end of today, you will have an answer to: How do we determine the average atomic mass of element from multiple isotopes? DO NOW: Fill out the data table using your knowledge of carbon Protons Neutrons Electrons Mass Number C-12 1. What is the atomic mass number of carbon found on the periodic table? 2. Which isotope of carbon do you predict would be the most common isotope of carbon? Explain your thinking. Hint: which isotopes mass is most similar to the mass we see on the periodic table? ELEMENT vs. ATOM vs. ISOTOPE 20 Ne 20 20 Ne Ne 20 Ne 21 22 Ne Ne 21 Ne With a partner, answer the following questions: 1. What element is represented by the particle diagram? 2. How many atoms of the element are there? 3. How many isotopes of the element are there? 4. Fill in the following chart: Isotope Mass Number % Abundance (What percent of all the atoms represented are of this particular isotope?) 22 Ne 20 Ne 22 Ne CHECK FOR UNDERSTANDING What are the differences between an element, atom, and isotope? What are the similarities? 5. Is it possible to answer the question, What is the mass of one neon atom? Why or why not?
PROCESS, THINK AND WRITE: Are all atoms of the same element identical to each other? Why or why not? Catalyzing Thoughts: Below are the two naturally occurring isotopes of boron. Three key numbers are highlighted. 1) Mass number of isotope (rounded) 2) Mass number of isotope (actual) Which whole number do you predict would be closest to the atomic mass for Boron found on the periodic table and WHY? The actual atomic mass number for Boron on the periodic table is: 10.81. This number is considered the average atomic mass. It is the weighted average of all of the different Boron isotopes. KEY VOCABULARY: 3) Percent Natural Abundance of that isotope ATOMIC MASS MASS NUMBER PROCESS, THINK AND WRITE: What is the difference between average atomic mass of an element and the mass number? APPLY: The atomic mass of an element is the weighted average of the (1) number of protons in the isotopes of that element (2) number of neutrons in the isotopes of that element (3) atomic masses of some of the naturally occurring isotopes of that element (4) atomic masses of all of the naturally occurring isotopes of that element
How to calculate average atomic mass: Work hard. Be nice. AVERAGE ATOMIC MASS = (mass of A)( % abundance of A in ratio form) + (mass of B)(% abundance of B in ratio form) +.. EXAMPLE 1: QUESTION Calculate the average atomic mass of boron. HOW TO SOLVE IT! EXAMPLE 2: Calculate the atomic mass of copper. Predict whether you think the answer will be closer to 63 or 65: Now solve: Atomic Mass = g/ mol
Name: Pd: Date: KIPP NYC College Prep General Chemistry 2.9 HW PART I: Complete Lab #8 Candium Lab! PART II: Be sure that all vocabulary words are in glossary sheets. The list of all words is on our website: http://chemistrykippnyc.weebly.com/ PART III: Study all vocabulary by covering the words or definitions and quizzing yourself PART IV: Multiple choice practice 1. The gold-foil experiment led scientists to conclude that an atom s (1) Positive charge is evenly spread throughout its volume (2) Negative charge is mainly concentrated in its nucleus (3) Mass is evenly spread throughout its volume (4) Volume is mainly empty space 2. In Rutherford s gold foil experiments, some alpha particles were deflected from their original paths but most passed with no deflection. Which statement about gold atoms is supported by these experimental observations? (1) Gold atoms consist mostly of empty space. (2) Gold atoms are similar to alpha particles. (3) Alpha particles and gold nuclei have opposite charges (4) Alpha particles are more dense than gold atoms. 3. The gold foil experiment led to the conclusion that each atom in the foil was composed mostly of empty space because most alpha particles directed at the foil (1) Passed through the foil (2) Remained trapped in the foil (3) Were deflected by the nuclei in gold atoms (4) Were deflected by the electrons in gold atoms 4. Which statement correctly describes the charge of the nucleus and the charge of the electron cloud of an atom? (1) The nucleus is positive and the electron cloud is positive. (2) The nucleus is positive and the electron cloud is negative. (3) The nucleus is negative and the electron cloud is positive. (4) The nucleus is negative and the electron cloud is negative. 5. Which subatomic particle has a negative charge? (1) Proton (2) Neutron (3) Electron (4) Positron 6. Which two particles each have a mass approximately equal to one atomic mass unit. (1) electron and neutron (2) electron and positron (3) proton and electron (4) proton and neutron 7. What is the charge of the nucleus of a nitrogen atom? (1) -7 (2) 0 (3) +7 (4) 14 8. The nucleus of an atom of K-42 contains (1) 19 protons and 23 neutrons (2) 19 protons and 42 neutrons (3) 20 protons and 19 neutrons (4) 23 protons and 19 neutrons
Name: Pd: Date: KIPP NYC College Prep General Chemistry WORK 2.7-Average Atomic Mass 10 points Summary Questions: A Nitrogen atom with 7 protons and 8 neutrons has a mass number of 15 amu. However, on the periodic table, the atomic mass for Nitrogen is 14.01. Explain how this is possible. In your own words, explain the difference between Mass Number and Average Atomic Mass. Regents-Style Questions 1. The atomic mass of an element is calculated using the (1) atomic number and the ratios of its naturally occurring isotopes (2) atomic number and the half-lives of each of its isotopes (3) masses and the ratios of its naturally occurring isotopes (4) masses and the half-lives of each of its isotopes 2. Hydrogen has three isotopes with mass numbers of 1, 2, and 3 and has an average atomic mass of 1.00794 amu. This information indicates that (1) equal numbers of each isotope are present (2) more isotopes have an atomic mass of 2 or 3 than of 1 (3) more isotopes have an atomic mass of 1 than of 2 or 3 (4) isotopes have only an atomic mass of 1 3. What whole number do you predict the atomic mass of sulfur to be closest to? 4. Show the numerical setup for calculating the average atomic mass of sulfur. 5. State, in terms of subatomic particles, one similarity and one difference between these isotopes of sulfur:
6. The table below shows the number of subatomic particles in atom X and in atom Z. Atom X and atom Z are isotopes of the element (1) aluminum (3) magnesium (2) carbon (4) nitrogen 7. The table below shows the various isotopes of Chlorine Mass Number 34.968852 75.77% 36.965903 24.23% Natural Abundance Determine the atomic mass of Chlorine: How many protons are found in Chlorine? How many electrons are found in Chlorine? Explain why the atomic mass number is closer to 35 than to 37. 8. Using the information below, calculate the average atomic mass of nitrogen. Mass Number 14.00307 99.63% 15.0001 0.37% Natural Abundance 6