Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
First Semester Exam Essays (2012) Essay Directions: Write out your responds ahead of time. Submit your responses before the exam starts on the exam day. You will NOT have the opportunity to respond during the exam period. 1. Compare and contrast solids, liquids, gases, and plasma by explaining the behavior of their particles. Draw models to illustrate your answer. 7. What can you determine about the atomic structure of an element if you know the atomic number of the element and mass numbers of its isotopes? What additional information is needed to determine the average atomic mass of the element? How do you determine the average atomic mass of the element? 2. Use examples to show how the properties and classifications of elements change as you move across a period of the periodic table. 8. Explain the significance of Avogadro's constant, 6.022 × 102 3. What is the relationship between it and the molar mass of oxygen, 16.00 g/mol? 3. Using the two models shown below explain how each model resembles the object it represents. Explain how each model differs from the object it represents. 9. Elements of the fourth period fill the 4s sublevel with electrons before filling the 3d sublevels. Also, some elements move an electron from a filled 4s sublevel to an unoccupied 3d sublevel. Explain these behaviors. 10. Explain nuclear charge and how it affects the general trend in radii of atoms of elements going from left to right across a period in the periodic table. 4. The table below show measurements made on samples of three unknown materials. Explain how this data could be used to identify the three materials. 11. Compare and contrast ionic and covalent bonding. Mass and Volume Data Material Mass (g) Volume (mL) 1 6.02 2.23 2 18.42 2.34 3 35.15 3.10 5. Explain what is meant by the law of definite proportions, the law of conservation of mass, and the law of multiple proportions. 6. Why do scientists use Dalton's theory, even though parts of it have been proven wrong? How much of Dalton's theory do scientists still accept? 1 ID: A First Semester Exam Essays (2012) Answer Section ESSAY 1. ANS: The arrangement of the particles in the three states accounts for their different properties. Particles in a solid move very little; particles in a liquid move more; and gas particles and plasma particles move the most. In drawn models, particles in solids should be closely packed and structured; particles in liquids should appear able to flow randomly past one another; and particles in gases should appear sparsely and randomly spaced. Plasma particles should have lost some of their electrons. PTS: 1 DIF: III REF: 2 OBJ: 3 STA: SC.A.1.4.3 2. ANS: The closer two elements are within a period, the more similar their properties are. Moving across a period, elements progress from metals to metalloids, to nonmetals, to noble gases. PTS: 1 DIF: III REF: 3 OBJ: 3 STA: SC.A.2.4.5 3. ANS: The model of the sun is accurate in showing that the sun is round and has a fiery surface. The model of an atom shows that the atom is a particle. The sun model is inaccurate because it is only two-dimensional, and it is smaller than the real sun. In addition, it does not show the sun's composition. The atomic model is inaccurate because it is larger than a real atom, because it is only two-dimensional, and because it does not depict the atom's composition and chemical properties. PTS: 1 DIF: III REF: 1 OBJ: 3 STA: SC.H.2.4.1 4. ANS: The density of each sample could be calculated. Then each value could be compared to known values to identify the substances. PTS: 1 DIF: III REF: 2 OBJ: 4 STA: SC.H.2.4.1 5. ANS: Definite proportions: regardless of the origin or size of samples of a particular compound, their elements are always in the same proportion. Conservation of mass: the mass of the elements combined in a compound is the same as the sum of the masses of the individual elements. Multiple proportions: when two elements combine to form two different compounds, the ratio of the masses of one element that combine with a fixed mass of the other element is a small whole number. PTS: 1 STA: SC.B.1.4.2 DIF: III REF: 1 OBJ: 1 1 ID: A 6. ANS: Dalton's theory led to the modern theory of the atom. Although scientists now know that atoms can be divided and that elements exist as isotopes, most of his early theory is still accepted. PTS: 1 DIF: II REF: 1 OBJ: 3 STA: SC.B.1.4.2 7. ANS: The atomic number equals the number of protons in the nucleus of an atom and also equals the number of electrons in the neutral atom. The mass number is the sum of the number of protons and neutrons and can be used, with the atomic number, to find the number of neutrons in each isotope. Each isotope of the element has a different mass number but the same atomic number as the element. In order to determine the average atomic mass of the element, you needed to know the relative abundance and the exact mass of each isotope. Then, multiply the relative abundance (in decimal form) times the atomic mass for each isotope, and adding the results. PTS: 1 DIF: II REF: 3 OBJ: 2 STA: SC.A.2.4.3 8. ANS: Avogadro's constant is the number of particles in 1 mol of a substance. Because the molar mass of oxygen atoms is 16.00 g/mol, the mass of 1 mol, or 6.022 × 102 3, oxygen atoms is 16.00 g. PTS: 1 DIF: II REF: 3 OBJ: 4 STA: SC.H.2.4.1 9. ANS: Elements fill the 4s sublevel with electrons before filling the 3d sublevels because the 4s sublevel is lower in energy than the 3d sublevels. According to the Aufbau principle, an electron occupies the lowest energy level that can receive it. Some elements move an electron from a filled 4s sublevel to an unoccupied 3d sublevel so they can have more unpaired electrons in their configuration. This minimizes electron repulsions and is therefore a more stable arrangement. PTS: 1 DIF: III REF: 3 OBJ: 2 10. ANS: Nuclear charge is the attraction an atomic nucleus has on the electrons surrounding it. As you move from left to right across a period, the atomic number increases, and therefore the number of protons in the nucleus increases. The more protons within a nucleus, the greater is the nuclear charge. A greater nuclear charge pulls the electrons closer to the nucleus, decreasing the atomic radius. PTS: 1 STA: SC.A.1.4.2 11. ANS: //// DIF: II REF: 3 OBJ: 2 PTS: 1 STA: SC.A.1.4.5 DIF: II REF: 2 OBJ: 5 2