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
Phys_SG_cap01-11.qxd 10/14/05 1:47 AM Page 125 Nombre Clase Fecha Hoja de destrezas Repaso de la sección El átomo USAR TÉRMINOS CLAVE 1. Escribe una sola oración con los siguientes términos: protón, neutrón e isótopo. Escoge el término correcto del banco de palabras para completar las siguientes oraciones. unidad de masa atómica número atómico número de masa masa atómica 2. El/La de un átomo es igual al número de protones que hay en su núcleo. 3. El/La de un átomo es igual al promedio ponderado de la masa de todos los isótopos de ese elemento que se encuentran en la naturaleza. COMPRENDER LAS IDEAS PRINCIPALES ______ 4. ¿Cuál de las siguientes partículas no tiene carga eléctrica? a. protón c. electrón b. neutrón d. ion 5. Nombra y describe las cuatro fuerzas que operan en el núcleo de un átomo. DESTREZAS MATEMÁTICAS 6. En su forma natural, el metal talio tiene 30% de talio 203 y 70% de talio 205. Calcula la masa atómica del talio. Muestra tu trabajo en el espacio en blanco. Copyright © by Holt, Rinehart and Winston. All rights reserved. HOLT CIENCIAS Y TECNOLOGÍA 125 Introducción a los átomos Phys_SG_cap01-11.qxd 10/14/05 1:47 AM Page 126 Nombre Clase Fecha Repaso de la sección (continuación) RAZONAMIENTO CRÍTICO 7. Analizar ideas ¿Por qué es tan pequeña la fuerza gravitacional en el núcleo? 8. Predecir consecuencias ¿Puede existir un núcleo con más de un protón pero sin ningún neutrón? Explica tu respuesta. INTERPRETAR GRÁFICAS 9. Observa los dos modelos atómicos siguientes. ¿Qué representan los dos átomos: elementos diferentes o isótopos diferentes? Explica tu respuesta. Protón Neutrón Protón Electrón Neutrón Electrón Copyright © by Holt, Rinehart and Winston. All rights reserved. HOLT CIENCIAS Y TECNOLOGÍA 126 Introducción a los átomos ANSWER KEY Vocabulary and Section Summary 5. He performed experiments and drew SECTION: DEVELOPMENT OF THE ATOMIC THEORY 6. 1. atom: the smallest unit of an element that maintains the properties of an element 2. electron: a subatomic particle that has a negative charge 3. nucleus: in physical science, an atom’s central region, which is made up of protons and neutrons 4. electron cloud: a region around the nucleus of an atom where electrons are likely to be found 7. 8. SECTION: THE ATOM 1. proton: a subatomic particle that has a 2. 3. 4. 5. 6. 7. 9. positive charge and that is found in the nucleus of an atom atomic mass unit: a unit of mass that describes the mass of an atom or molecule neutron: a subatomic particle that has no charge and that is found in the nucleus of an atom atomic number: the number of protons in the nucleus of an atom; the atomic number is the same for all atoms of an element isotope: an atom that has the same number of protons (or the same atomic number) as other atoms of the same element do but that has a different number of neutrons (and thus a different atomic mass) mass number: the sum of the numbers of protons and neutrons in the nucleus of an atom atomic mass: the mass of an atom expressed in atomic mass units 10. conclusions from them to develop his theory. Rutherford’s gold foil experiment, in which Rutherford observed that most of the positively charged particles that he aimed at a piece of gold foil went straight through Bohr suggested that electrons could move around the nucleus only in certain paths. They could jump from path to path, but not stay between the paths. Bohr’s theory held that electrons can travel only in certain paths around the nucleus. The current atomic theory is that electrons travel in regions where they are likely to be found. Rutherford placed a surface behind the gold foil, which would glow where the positively charged particles hit it. This shows that he was trying to find out where the particles went after hitting the gold foil. The model represents electrons as mixed throughout an atom. Rutherford showed this arrangement to be incorrect. SECTION: THE ATOM 1. Sample answer: Different isotopes 2. 3. 4. 5. Section Review SECTION: DEVELOPMENT OF THE ATOMIC THEORY 6. 1. Sample answer: the smallest part of an 7. element that has the properties of that element 2. electron 3. nucleus 4. B 8. have the same number of protons but different numbers of neutrons. atomic number atomic mass B Gravitational force acts between objects based on their mass. Electromagnetic force attracts objects of opposite electric charge and repels objects of the same electric charge. The strong force holds the protons and neutrons of atomic nuclei together. The weak force plays a role in radioactive decay. (0.30 203 amu) (0.70 205 amu) 204.4 amu Gravitational force in the nucleus is so small because the masses of nuclear particles are so small. no; Without neutrons, two protons brought into close contact would repel each other. Copyright © by Holt, Rinehart and Winston. All rights reserved. Holt Science and Technology 62 Introduction to Atoms ANSWER KEY Reinforcement 9. The two atoms shown are different elements—they have different numbers of protons. A. B. C. D. E. F. G. H. I. J. K. L. Chapter Review 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. Protons protons Neutrons mass number atomic mass C A D A B electromagnetic force Sample answer: The plum-pudding model describes the atom as a lump of positively charged material with negatively charged particles throughout. The positively charged material is like the pudding, and electrons are like plums in the pudding. (0.60 69 amu) (0.40 71 amu) 69.8 amu number of protons atomic number 40 number of neutrons mass number – atomic number 50 number of electrons number of protons 40 An answer to this exercise can be found at the end of the Teacher Edition. Scientists must determine the atomic number, or the number of protons, in the newly formed nucleus. The nucleus is that of a new element only if the number of protons is different from all known elements. Sample answer: Dalton’s atomic theory was the first one based on experimental evidence. It helps show how a theory develops as new information is discovered. No, the results of an experiment must be repeatable to be considered valid. A and C 3 7 M. N. O. P. Q. R. S. T. Rutherford, 1909–1911 Rutherford, 1909–1911 Thomson, 1897 Bohr, 1913 Dalton, 1803 Thomson, 1897 Democritus, 440 BCE Rutherford, 1909–1911 Democritus, 440 BCE Dalton, 1803 Bohr, 1913 Schrödinger and Heisenberg, twentieth century Thomson, 1897 Rutherford, 1909–1911 Dalton, 1803 Schrödinger and Heisenberg, twentieth century Dalton, 1803 Democritus, 440 BCE Rutherford, 1909–1911 Dalton, 1803 Critical Thinking 1. Because the nucleus is positively 2. 3. 4. 5. 6. charged, the suit also must have been positively charged to create this repulsion. Her suit would have had a neutral charge. Answers may vary according to the forces students discuss. Sample answer: If her suit was positively charged, then the electromagnetic force would pull her toward the electrons in the atom. Knowing that the atomic number of carbon is six, Professor Pending could look for an atom with six protons in its nucleus. An atom’s mass number is equal to its protons plus its neutrons. All carbon atoms have six protons. Carbon-14 would have six protons and eight neutrons. Professor Pending could use this characteristic to identify the correct atom. A negatively charged ion has more electrons than protons. Therefore, the ion would require at least seven electrons. Copyright © by Holt, Rinehart and Winston. All rights reserved. Holt Science and Technology 63 Introduction to Atoms