The following data for the Sun and the four inner planets of the Solar System have been observed. Diameter (kilometers)

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1 The following data for the Sun and the four inner planets of the Solar System have been observed. Mean Distance from the Sun (million kilometers) Diameter (kilometers) Sun 1,400,000 Mercury 58 4,900 Venus ,100 Earth ,800 Mars 228 6,800 In a simplified model of the Solar System, the planets revolve around the Sun in circular orbits, all in the same plane. Each planet has a different period of revolution. Also, each planet is a sphere that rotates about an axis through its center, but with a different period of rotation. In this model the axis of rotation of each planet is perpendicular to the plane of the orbit.

2 1. Describe two similarities and two differences between this model of the atom and the simplified

3 Scoring Guide Score & Description Complete Student demonstrates an understanding of the simple models of the Solar System and the atom by pointing out two similarities and two differences between these two models. Essential Student response contains two correct similarities and one correct difference or one correct similarity and two correct differences. Adequate Student response contains one correct similarity and one correct difference, or two correct similarities or two correct differences. Partial Student response contains one correct similarity or difference. Unsatisfactory/Incorrect Student response contains no correct similarities and no correct differences. Credited similarities: a. Most mass in center, or: nucleus/sun at center, or: both systems have a central mass/object. b. Orbits are nearly circular. c. Attractive force between central and orbiting objects (central force). d. Objects in orbit, or: there are orbits around a center. e. Items rotate on an axis (electrons/planets). f. Analogous components: Sun similar to nucleus, planets similar to electrons. g. Both models are simplified views of complex ideas. h. Both systems are always in motion. Credited differences: a. Size or scale of objects/distances between objects. b. Nature of forces between orbiting and central objects (i.e. electrostatic vs. gravitational). c. Period of revolution of orbiting objects. d. More than one electron is possible in each orbit, as opposed to only one planet per orbit in Solar System. e. Composed of different components with some mention of what the different components are. f. The shapes of the orbits are different.

4 Complete - Student Response Student response provides two correct similarities and two correct differences. Student response provides two correct similarities: (1) presence of a central mass; (2) object revolving around central body. Response provides two correct differences: (1) more than one mass is allowed in an orbit of an atom, implying that in the Solar System there can only be one mass per orbit; (2) the shapes of the orbits are different. Essential - Student Response

5 Student response provides two correct similarities: (1) planets/electrons revolving around Sun/nucleus; (2) force of attraction between components within the respective systems. Response provides one correct difference: presence of particles in the nucleus. Student response provides one correct similarity: planets/electrons revolving around Sun/nucleus. Response provides two correct differences: (1) presence of particles in the nucleus; (2) atom is smaller. There is mention of electrons orbiting in different levels, but there is no clear indication about the unique ability of electrons to "leap" from one orbit to another. Adequate - Student Response

6 Student response provides two correct differences only: (1) presence of particles in the nucleus; (2) only one planet while more than one electron possible in one orbit. Student response provides one correct similarity: analogous components, electrons -- planets, nucleus -- Sun; one correct difference: electrons may pair up (in an orbit), while planets may not. Statement about more electrons being present in an atom than planets in the Solar System is incorrect because an atom can have more or less electrons depending on which element it represents. Partial - Student Response

7 Student response provides one correct difference: size/scale of objects. It is incorrect to state that the Solar System has more components than an atom because an atom can have more or less components depending on which element it represents. Student response provides one correct difference: the models have changed over time. Unsatisfactory/Incorrect - Student Response

8 Both statements in the response are incorrect. Student response simply states that the models represent the real systems, but does not state any similarities or differences.

9 2000 National Performance Results Score Percentage of Students Unsatisfactory/incorrect 30% Partial 20% Adequate 18% Essential 7% Complete 2% Omitted 21% Off task 3% Note: These results are for public and nonpublic school students. Percentages may not add to 100 due to rounding. The Fields of Science: Physical Sciences (Sub content classification: Matter and Its Transformations) Knowing and Doing Science : Conceptual Understanding

10 The Fields of Science Physical Sciences This question measures basic knowledge and understanding of the following: Knowing and Doing Science Conceptual Understanding Conceptual understanding includes the body of scientific knowledge that students draw upon when conducting a scientific investigation or engaging in practical reasoning. Essential scientific concepts involve a variety of information, including facts and events the student learns from both science instruction and experiences with natural environment; and scientific concepts, principles, laws, and theories that scientists use to explain and predict observations of the natural world.