Bean Counting Teacher Notes and Materials 1.3: Elements
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Developmental Lesson FC #1.3: Bean Counting Teacher Notes and Materials 1.3: Elements Goal Facets: 01 The student understands that in every atom that makes up one kind of element, the number of protons is the same, but the number of neutrons or electrons may vary. 02 The student understands that all substances come from a limited number of elements in our universe. 03 The student knows that the nucleus of an atom does not change easily, which explains why we cannot easily make one element from another element. 04 The student knows that an atom's identity remains the same regardless of the state of matter or the type of matter of which it is a part. Background The entire universe consists of only a limited number of elements, which make up everything that we experience in our daily lives as well as the stars and galaxies, which shine millions of light-years away. An atom of a particular element can be identified by the number of protons in its nucleus. For example, if an atom has 11 protons it is a sodium atom. If the number of protons is not 11, then it is not sodium. For any given element, the number of neutrons or electrons may vary without altering the identity of the element. For example, one fluorine atom may have 9 protons and 9 neutrons while another fluorine atom may have 9 protons and 10 neutrons. These are said to be two different isotopes of fluorine. Isotopes are atoms of an element with different numbers of neutrons. Atoms of one element don’t easily change into atoms of another element. However, they may gain or lose electrons to become ions. An atom of fluorine may gain an electron from some other atom, in which case it would now have a charge of -1. Even though it has gained an electron, it is still fluorine because the number of protons has not changed. Materials: • Student handout • Beans (2 distinct types) Procedure: Considering the following substances and their chemical formulas: 1. Liquid water, H2O 2. Ice, H2O 3. Water vapor, H2O 4. Diamond, C 5. Graphite, C 6. Carbon dioxide gas, CO2 7. Sucrose (sugar), C12H22O11 Developmental Lesson FC #1.3: Bean Counting Teacher Notes and Materials From the beans provided, choose one kind to represent protons and another to represent neutrons. Place the appropriate numbers of each kind of bean in the boxes below to represent the elements indicated. Liquid water, H2O Ice, H2O Hydrogen Oxygen Hydrogen Oxygen Water vapor, H2O Hydrogen Oxygen Diamond, C Graphite, C Carbon Carbon Carbon dioxide gas, CO2 Carbon Oxygen Developmental Lesson FC #1.3: Bean Counting Teacher Notes and Materials Sucrose, C12H22O11 Carbon Hydrogen Oxygen Discussion Questions 1. Which subatomic particle determines the identity of an atom? 2. How did you decide how many neutrons to put in each box? 3. Does the atom change when it is a part of a different state of matter (solid, liquid, gas)? 4. Does the atom change when it is part of a different compound (e.g. carbon in carbon dioxide versus sucrose)? 5. How many different elements make up the seven substances examined in this activity? 6. Look at the Periodic Table of the Elements. How many elements are there? 7. Do you think it is possible for other elements to exist? How would they be different than those on the periodic table? Developmental Lesson FC #1.3: Bean Counting Teacher Notes and Materials Teacher Notes: In this activity students will play with the roles of protons and electrons within atoms to study the concepts of attraction to the nucleus, how the number of energy levels affects the size of the atom, ionization energy and bonding. Before doing the activity students will need to know how to determine the number of protons and neutrons in an atom from the periodic table. On the periodic table the atomic number tells you how many protons are in an atom of an element. For example, Aluminum has an atomic number of 13 and therefore has 13 protons. To find the number of neutrons you subtract the number of protons from the mass number. On the periodic table, you can round the atomic mass to the nearest whole number and use that value as the mass number. You can also teach about percent abundances and atomic mass, but this is not necessary for successful performance in the activity. The atomic mass of an element is the weighted average of the naturally occurring isotopes of an element. For example, iron exists as four naturally occurring isotopes with the following abundances: Isotope Atomic mass Percent (amu) abundance Fe-54 53.9396 5.84% Fe-56 55.9349 91.75% Fe-57 56.93539 2.12% Fe-58 57.93328 0.282% To find the average atomic mass of an element, multiply the atomic mass of each isotope by its percent abundance, expressed as a decimal, and add all of these values together. (53.9396 x 0.0584) + (55.9349 x 0.9175) + (56.93539 x 0.0212) + (57.93328 x 0.00282) = 3.1501 + 51.3203 + 1.2070 + 0.1634 = 55.84 amu Remind the students that the atomic mass is determined almost entirely by the mass of the protons and neutrons, as the mass of an electron is approximately 1/1800 the mass of a proton or neutron. Questions number 7 asks students to look at the periodic table and tell how many elements there are. Their answer will depend on the date the table was created. You can address this by Developmental Lesson FC #1.3: Bean Counting Teacher Notes and Materials explaining the difference between the naturally occurring elements and the man-made elements. There are 92 elements which occur naturally on earth – all those up to # 94 (Uranium) except for #43 (Technetium) and #61 (Promethium). Technetium has not been found on earth. It has been produced in the lab and has been detected in the spectra of stars other than the sun. All of the Promethium that was originally present when the earth formed has disappeared due to radioactive decay. Promethium occurs only in small trace amounts in uranium ores as a fission product. Its longest-lived isotope has a half-life of 17.7 years. Elements with atomic numbers of 95 to 118 have been synthesized. This is done in particle accelerators and requires huge amounts of energy – far more than can be supplied by ordinary chemical reactions. References: Steam image taken from: http://en.wikipedia.org/wiki/File:Steam_Phase_eruption_of_Castle_geyser_with_double_rainb ow.jpg Diamond image taken from: http://topforeignstocks.com/wp-content/uploads/2010/06/diamond.jpg Carbon dioxide image taken from: http://www.scienceclarified.com/Ca-Ch/Carbon-Dioxide.html Sugar image taken from: http://brooklynimbecile.files.wordpress.com/2010/03/refined_sugar-137163701.jpg .