Honors Chemistry Unit 2: The Atom & Its Nucleus

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1 Honors Chemistry Unit 2: The Atom & Its Nucleus ( ) Bunsen, I must tell you how excellent your study of chemical spectroscopy is, as is your pioneer work in photochemistry but what really impresses me is that cute little burner you ve come up with. History of the atomic theory Atomic structure Isotopes Ions Average atomic mass % abundance Nuclear chemistry/reactions o Radioactive decay & types of radiation o Radioactive decay rate Half-life o Fission o Fusion 1

2 At the conclusion of this unit, the student will be able to: 1. Describe the development of the atomic theory. 2. Describe the law of conservation of mass/matter. 3. Describe the law of definite proportions. 4. Describe the law of multiple proportions. 5. Describe the location and amount of the subatomic particles for a specific isotope. 6. Define and distinguish between an ion and an atom. 7. Calculate the average atomic mass of an element or isotope percent/relative abundances. 8. Identify the different types of nuclear reactions 9. Compare and contrast fusion and fission. 10. Calculate half-life We are looking for: 1a. Description of each scientists contribution to the development of the atomic theory. 2. Law of conservation of mass/matter: matter cannot be created nor destroyed (Lavoisier). 3. Law of definite proportions: atoms combine in specific whole number ratios (Proust). 4. Law of multiple proportions: two elements can combine in different ratios to form different compounds; ex. CO and CO2 (Dalton). 5a. Isotopes are atoms of the same element that differ in the number of neutrons. 5b. The nucleus is the center of the atom and contains protons and neutrons. 5c. An atom contains the same number of protons and electrons to remain neutral. 6. An ion contains a different number of protons and electrons to give it an overall charge. 7a. Given the isotope percent/relative abundances or number of atoms in a sample and masses of each, calculate the average atomic mass of the element (round at the end to keep 2 decimal places). 7b. Given the average atomic mass and number of isotopes, calculate the percent/relative abundances of each isotope (round at the end to keep 2 decimal places). 8a. Identify and calculate the following nuclear reactions (alpha, beta, gamma, positron, and electron capture) 9a. Fission is the splitting of a nucleus into small fragments 9b. Fusion is the combining of two nuclei 10a. Half-life is a measure of the rate of radioactive decay, or the amount of time it takes for half of a radioactive sample initially present to decay to its products 2

3 Honors Chemistry Worksheet Atomic Theorists 1. Who: What: Law of Conservation of Mass 2. Who: What: Law of Definite Proportions 3. Who: What: Law of Multiple Proportions When: Where: When: Where: When: Where: 4. Who: Aristotle What: 5. Who: Democritus What: 6. Who: John Dalton What: When: Where: When: Where: When: Where: 3

4 7. Who: J.J. Thomson What: 8. Who: Robert Millikan What: 9. Who: Ernest Rutherford What: When: Where: When: Where: When: Where: 10. Who: Niels Bohr What: 11. Who: Erwin Schrodinger What: 12. Who: James Chadwick What: When: Where: When: Where: When: Where: 4

5 Name Class Period Honors Chemistry Problems with Dalton s Theory 1. Matter is composed of indivisible particles 2. All atoms of a particular element are identical 3. Different elements have different atoms 4. Atoms combine in certain whole-number ratios 5. In a chemical reaction, atoms are merely rearranged to form new compounds; they are not created, destroyed, or changed into atoms of any other elements. 5

6 Name Class Period Honors Chemistry Worksheet "Review Atomic Theorists" Directions: Match the person or term on the left to the picture on the right. Aristotle Democritus Erwin Schrodinger Niels Bohr JJ Thomson Ernest Rutherford John Dalton Solid Sphere Model Plum Pudding Model Mass Centered/Stationary Planetary Model Pulsating Planetary Model Pulsating Orbital Model 6

7 Name Class Period Honors Chemistry Worksheet Atomic Theorists & Atomic Structure Review 1) Neutral particles. 2) Scientist who discovered the electron. He also did work with isotopes. The experiments he did used the cathode ray tube. 3) Mass is neither created nor destroyed. 4) Value represented by # of protons + # of neutrons. 5) He founded the mathematical model of the atom. The electrons are located in the electron cloud. 6) The one element that has an isotope that does not contain all of the subatomic particles.(hint: lightest element) 7) Whenever two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers. 8) He developed the pulsating planetary model, where electrons can change orbitals. 9) The Greek philosopher who believed in the atom. 10) A negatively charged particle that is located outside of the nucleus. 11) This refers to electrons, neutrons, and protons. 7

8 12) Atoms with the same number of protons and electrons but a different number of neutrons. 13) This scientist used the oil drop experiment to discover the mass of the electron. 14) A positively charged particle. 15) Chemical compounds have the same elements in exactly the same ratios. 16) This English scientist is credited with discovering the neutron. 17) It represents the number of protons in the nucleus of an atom. 18) A formula for representing an element that uses the element symbol, the mass number, and the atomic number. 19) A scientist whose research lead to the discovery that the nucleus is small, dense, and positively charged. The electrons orbit around the nucleus. The experiment he used is known as the gold foil experiment. 20) Smallest particle of an element that retains the chemical properties of that element. 21) A naming method that uses the name (or symbol) of the element followed by a dash and its mass number. 22) A Greek philosopher who did not believe in the atom. His theory involved the natural elements of fire, water, air and Earth. 23) His atomic theory model was represented by a simple solid sphere. 8

9 Isotopes Atomic # = # protons (p + ) Mass Number= # protons (p + ) + # neutrons (n o ) this is a whole number Hyphen notation = Atomic symbol hyphen (not subtraction) followed by mass number = H-2 (Hydrogen w/ a mass of 2 amu) Nuclear Symbol notation = Mass # Atomic #(Atomic Symbol) 2 = 1 H (Hydrogen w/ a mass of 2 amu) Use a periodic table and the notes from above to fill in the missing data in the table below: Nuclear Symbol notation 65 29Cu 86 Kr Number of protons Number of neutrons Number of electrons in the neutral atom Name of element Boron Hyphen notation Au-198 9

10 Atom: -electrically neutral; the number of electrons and protons are equal. Ion: -an electrically charged atom (positive or negative). -the number of electrons and protons are not equal. Cation: -a positively charged ion. Ex) Na tends to lose one electron to form a 1+ ion, Na + Ca tends to lose two electrons to form a 2+ ion, Ca 2+ Anion: -a negatively charged ion. Ex) Cl tends to gain one electron to form a 1- ion, Cl - O tends to gain two electrons to form a 2- ion, O 2- Fill in the missing information in the table below: Hyphen notation Nuclear Symbol notation Number of protons Number of neutrons Al-27 He-4 Li U Number of electrons Atom, Cation, or Anion Overall charge Atomic Number atom

11 Calculating Average Atomic Mass Average atomic mass: -The weighted average of all the naturally occurring isotopes for a given element. -This is NOT a mathematical average! -This is the mass listed on the periodic table. Percent (%) Abundances: -the percentage of each isotope for a given element. -the percent abundances of all the isotopes for a given element add up to 100. Relative Abundance: -the percent abundance of an isotope divided by the relative abundances of all the isotopes for a given element add up to 1. Relative Mass: -the product of the relative abundance and the mass number for an isotope of a given element. **The Average Atomic Mass is the sum of all the relative masses for a given element.** Do NOT divide your answer!! Units on average atomic mass are amu (atomic mass units). Round your final average atomic mass answer to 2 decimal places! 11

12 Ex) Iron has 4 naturally occurring isotopes. Iron s composition breaks down as follows: 5.845% Fe % Fe % Fe % Fe-58 1) Convert all the % abundances to relative abundances ) Multiply the relative abundance times the mass number to obtain relative mass x 54= x 56= x 57= x 58= ) Add the relative masses together = ) Round the answer to 2 decimal places ) Put units on your answer; amu amu 12

13 Name Class Period Honors Chemistry Worksheet Determining Average Atomic Mass of an Element Calculating Average Atomic Mass for Argon (round all answers to 2 decimal places): 1. Determine the average atomic mass for Argon which has 3 naturally occurring isotopes: 0.337% abundance of Ar % abundance of Ar % abundance of Ar-40 Calculated Average Atomic Mass of Argon: 2. Determine the Average Atomic Mass of Sulfur which has 4 naturally occurring isotopes: % abundance of S % abundance of S % abundance of S % abundance of S-36 Calculated Average Atomic Mass 13

14 3. Determine the Average Atomic Mass of Zinc which has 5 naturally occurring isotopes: % abundance of Zn % abundance of Zn % abundance of Zn % abundance of Zn % abundance of Zn-70 Calculated Average Atomic Mass 14

15 Name Average Atomic Mass Calculation Based on the number of atoms 1. Nitrogen has two isotopes with the following distributions: 99 atoms out of 100 atoms of nitrogen are 1 atom out of 100 atoms of nitrogen are 14 7 N 15 7 N Class Period The average atomic mass of Nitrogen is. 2. Antimony has two isotopes with the following distributions: 121 Sb 29 atoms out of 50 atoms of antimony are atoms out of 50 atoms of antimony are Sb The average atomic mass of Antimony is. 3. Copper has two isotopes with the following distributions: 63 Cu 25 atoms out of 35 atoms of copper are atoms out of 35 atoms of copper are 65 Cu 29 The average atomic mass of Copper is. 15

16 Purpose: Candium Lab To analyze the isotopes of candium and to calculate its average atomic mass. Materials: sample of candium balance cups Procedure: (record all your data & calculations in the data table!) 1) Obtain a sample of candium. 2) Separate the sample into its 3 isotopes (m&m s, skittles, and Reese s pieces). 3) Measure the total mass for each isotope; all the m&m s, all the skittles, all the Reese s. 4) Count the number of atoms in each isotope. 5) Calculate the mass of one atom for each isotope using the total mass and number of atoms. 6) Calculate the % abundance for each isotope using the number of atoms for each isotope and the total number of atoms in the entire candium sample. 7) Calculate the average atomic mass for candium using the % abundance and mass of one atom for each isotope. Show your work beneath the data table! 8) To check your answer, remember that the average atomic mass should be closest to the most abundant isotope s mass. Total mass m&m s skittles Reese s pieces Number of atoms Mass # (mass of one atom of this isotope; do NOT use the balance!) % abundance Show your work below for the average atomic mass calculation: 16

17 Calculating Isotope % Abundances You will only be calculating percentages for elements that have 2 isotopes. You will be given the 2 isotopes with their mass numbers. Use the periodic table for the average atomic mass for the element. 1) Set one of the isotope s relative abundance equal to X. 2) The relative abundances must add up to 1; therefore, the other isotope s relative abundance would be equal to 1-X. 3) Remember, the relative mass is equal to the relative abundance times the mass number. Remember, the relative masses must add up to the average atomic mass. 4) Setup an algebraic equation where the relative masses of each isotope is set equal to the average atomic mass for the element. Use the full average atomic mass from the periodic table, do NOT round. (X mass number) + [(1-x) mass number] = average atomic mass *When solving for X, keep 4 decimal places. This will allow the % abundance to have 2 decimal places. 5) X is the relative abundance, so multiply this by 100 to make it % abundance. 6) To obtain the other isotope s % abundance, the 2 % abundances must add up to

18 Ex) Determine the % abundance for each isotope of antimony. Antimony exists as Sb-121 and Sb-123. (X 121) + [(1-X) 123] = X X = X = X = The relative abundance of Sb-121 is ; therefore, the % abundance of Sb-121 is 62.00% and the % abundance of Sb-123 is 38.00% (100-62=38). Try this one: Potassium exists as K-39 and K-41. Determine the % abundance for each isotope of potassium. 18

19 Name Class Period Honors Chemistry Worksheet Calculating % Abundance of Isotopes of an Element 1. Determine the % Abundance of the two isotopes of Copper (Cu-63 and Cu-65) Based on the average atomic mass of Copper, which isotope should have the higher percentage? Circle: Cu-63 and Cu-65 % abundance of Cu-63 % abundance of Cu Determine the % Abundance of the two isotopes of Boron (B-10 and B-11): % abundance of B-10 % abundance of B-11 19

20 3. Determine the % Abundance of the two isotopes of Chlorine (Cl-35 and Cl-37): % abundance of Cl-35 % abundance of Cl Determine the % Abundance of the two isotopes of Carbon (C-12 and C-13): % abundance of C-12 % abundance of C-13 20

21 Isotopes of Coinium Lab: Name: Penny data: Part A: Find the mass of 5 old pennies and then determine the average mass of just 1 old penny (pre-82 penny). Mass of 1 old penny= Find the mass of 5 new pennies and then determine the average mass of one new penny (post-82 penny) Mass of 1 new penny= Problems: Sample #1 contains 3 old and 7 new pennies; calculate the average atomic mass of a penny in this sample. Show your work below: Average atomic mass of sample #1= Is the average atomic mass for this sample closer to the mass of an old penny or a new penny? Why does this occur? Sample #2 contains 6 old and 4 new pennies; calculate the average atomic mass of a penny in this sample. Show your work below. Average atomic mass= Is the average atomic mass for this sample closer to the mass of an old penny or a new penny? Why does this occur? 21

22 Part C: The Mystery Sample 1) Get a canister of pennies. Don t open it! Record its identifying number or letter: 2) Record the mass of the empty film canister, which is on the label of the canister. 3) Find the mass of the sealed film canister containing ten pennies. 4) Return the canister to your teacher. 5) Calculate the mass of just the ten pennies. 6) Calculate the average mass of one penny in the canister. (your answer from # 5 divided by 10). 7) Calculate the relative abundance for each penny in the sample (number of old pennies and number of new pennies). Remember to set one of the relative abundances to X and the other to 1-X because the relative abundances must add up to equal 1. 8) a) Relative abundance of old pennies= b) Relative abundance of new pennies= 9) a) % abundance of old pennies= b) % abundance of new pennies= 10) Your sample contained 10 total pennies. How many pennies were old? How many pennies were new? 22

23 Name Fill in the Blanks! Element Name Symbol & Charge (If it is an ion) Atom, anion, or cation? Atomic Number Mass Number (for this isotope) # of Protons # of Electrons # of Neutrons (for this isotope) Ru atom atom Ce 82 H 1 1 Fe Cl List the number of protons, electrons, and neutrons in each pair of isotopes: # of Protons # of Electrons # of Neutrons 6 3 Li 7 3 Li Ca Ca Write the Hyphen Notation and the Nuclear Symbol for the 1 st 5 elements (isotopes) in the chart at the top of this paper. Element Hyphen Notation Nuclear Symbol 1. Ruthenium

24 Name 1. Atomic # = 56 Mass Number = 137 a) # of Protons b) # of Electrons c) # of Neutrons d) Hyphen notation e) Nuclear Symbol f) Name of element Honors Chemistry Worksheet "Review Atomic Theory" 2. Which of the following nuclear symbols represent isotopes of the same element? A. B. C. D. 131 X 141 X 133 X 139 X Calculate the average atomic mass for Zinc: Element % Abundance Zn Zn Zn Zn Zn Compare your value with the Average atomic mass number for Zinc (Zn) on the Periodic Table. 4. Calculate the % abundance for Gallium Element Gallium % Abundance Ga-69 Ga Calculate the average atomic mass for X: Element Number of Atoms/50 X atoms X-36 8 atoms X-37 1 atom #6-8, you ll need to complete these on a separate sheet of paper. 6. Review Atomic Theorists from the Greeks to the Modern Era. Draw the picture of their atomic model (Democritus does not have a picture) and know the name of that theory (we had a handout with all of them on there Example: JJ Thomson s theory is represented by the plum pudding or jello salad model.) Democritus Aristotle John Dalton JJ Thomson Robert Millikan Ernest Rutherford Niels Bohr James Chadwick Erwin Schrodinger 7. List three experiments of the atomic theory, who did them and what we learned from them. 8. List three laws that govern chemistry that were discussed in class, who wrote them and what did they say. 24

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29 Write the nuclear reaction for each problem. 1) Show Bi-209 undergoing alpha decay. Nuclear Decay Practice Problems 2) Show At-210 undergoing gamma emission. 3) What is the particle that is emitted when U-238 decays into Th-234? 4) When Po-216 emits a beta particle what daughter nuclide is formed? 5) When Po-216 emits an alpha particle what daughter nuclide is formed? 6) What is the parent nuclide if alpha decay occurs and forms Ac-230? 7) What is released when Rn-220 captures an electron? 8) What daughter nuclide is formed when Rn-220 undergoes positron emission? 9) What is emitted when Bi-210 decays into Pb ) What is the parent nuclide if beta decay occurs and forms Na-24? 11) What parent nuclide captured an electron if Radium-226 is formed? 12) What daughter nuclide is formed when Am-244 undergoes beta emission? 13) Show Pu-239 undergoing alpha decay twice (show alpha decay of Pu-239 then another alpha decay of the daughter nuclide). 29

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31 Half-Life Practice Problems 1) The half-life of radon-222 is days. How many days is 4 half-lives? 2) Phophorus-32 has a half-life of 14.3 days. If you start with a 2.00 gram sample, how many grams will remain after 28.6 days? 3) A 10.0 gram sample of a particular radioactive isotope has a half-life of minutes. After minutes, how many grams of the sample remains? 4) The half-life of polonium-218 is 3.0 minutes. If you start with a 16.0 mg sample, how long will it take before only 1.0 mg remains? 31

32 Name: Half-Life Worksheet 1) The half-life of cobalt-60 is 5.3 years. How much of a gram sample of cobalt-60 is left after 15.9 years? 2) The half-life of radium-224 is 3.66 days. What was the original mass of radium-224 if 0.05 grams remains after 7.32 days? 3) After 4797 years, how much of an original 0.25 grams sample of radium-226 remains if its halflife is 1599 years? 4) Nitrogen-13 emits beta radiation and decays to carbon-13 with a half-life of 10 minutes. Assume a starting mass of 2.00 grams of nitrogen-13. How long is three half-lives? 5) Carbon-11, used in medical imaging, has a half-life of 20.5 minutes. The carbon-11 nuclides are formed and then incorporated into a desired compound. The resulting sample is injected into a patient, and the medical image is obtained. The entire process takes five half-lives. What percentage of the original carbon-11 remains at this time? 6) Given that the half-life of carbon-14 is 5730 years, consider a sample of fossilized wood that, when alive would have contained 24 grams of carbon-14. It now contains 1.5 grams of carbon- 14. How old is the sample? 32

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