Introduction to Atoms

Transcription

1 Introduction to Atoms Understanding Main Ideas Answer the following questions on a separate sheet of paper. 1. What three particles are found in an atom? 2. Which two particles are found in an atom s nucleus? 3. Explain why scientists use models to study atoms. 4. Which two particles in an atom are equal in number? 5. How are elements identified in terms of their atoms? 6. What two particles account for almost all of the mass of an atom? Building Vocabulary Fill in the blank to complete each statement. 7. The is the very small, dense center of an atom. 8. The positively charged particle of an atom is called a(n). 9. A particle with no charge is a(n). 10. A(n) is the particle of an atom that moves rapidly in the cloudlike region around the nucleus. 11. The tells the number of protons in the nucleus of every atom of an element. 12. Atoms of the same element that have the same number of protons but different numbers of neutrons are called. 13. The sum of protons and neutrons in the nucleus of an atom is the. 14. Scientists will often use a(n), an object that helps explain ideas about the natural world. 79D

2 Introduction to Atoms Read the passage and study the figure below it. Then use a separate sheet of paper to answer the questions that follow the figure. Exactly How Small Is It? Measuring the size of an atom is not easy. For one thing, an atom is very, very tiny. Scientists, however, have developed several ways to estimate the relative sizes of atoms. For elements that exist as two identical molecules bonded together, such as oxygen and hydrogen, scientists can use a technique called X-ray diffraction to estimate the distance between the nuclei. Once scientists do that, they can calculate the atomic radius, which is one-half the distance between the nuclei. It s important to remember that the atomic radius is not a measurement of a single atom s size but only its size relative to other atoms. In other words, scientists know that oxygen atoms are larger than hydrogen atoms, but they don t know the exact size of any single atom of oxygen. When comparing sizes of atoms, one must be careful to compare sizes based on similar measuring techniques. The figure below shows the atomic radii of several elements. The atomic radius is given in units of picometers (pm). One picometer is equal to meter. 1. What part of an atom determines its size? 2. Why is it difficult to measure the size of an atom? 3. What is the distance between nuclei in a hydrogen molecule (H 2 )? 4. What would be the distance between nuclei of a bromine molecule (Br 2 )? 5. What is the atomic radius of oxygen in meters? 6. Which atoms are relatively larger than oxygen atoms? 79E

3 Organizing the Elements Understanding Main Ideas The diagram below is a square from the periodic table. Label the four facts shown about each element Answer the following questions in the spaces provided. 5. In what order did Mendeleev arrange the elements in the periodic table? 6. What do elements in the same column in the periodic table have in common? 7. What can you predict about an element from its position in the periodic table? Building Vocabulary Fill in the blank to complete each statement. 8. An element s is its row in the periodic table. 9. The of an element is the average mass of all isotopes of that element. 10. A(n) is an abbreviation for the name of an element and usually has either one or two letters. 87E

4 Organizing the Elements Read the passage and look at the diagram and table below it. Then use a separate sheet of paper to answer the questions that follow the diagram and table. Properties of a Missing Element To some scientists of the early 1870s, Dmitri Mendeleev s periodic table of the elements was not very good. They criticized the table because it had gaps in it. Mendeleev, however, believed the gaps would someday be filled by elements that had not yet been discovered. In 1871, he predicted some of the properties of a yet-to-be-discovered element. He called it ekasilicon. The missing element was not discovered until Imagine you are a chemist living in Study the section of the periodic table shown below as well as the accompanying table of properties. (Scientists in 1880 hadn t learned what atomic numbers are. They also used bonding power to describe the number of chemical bonds an element could form.) Atomic mass Ga 70 Si 28 Ekasilicon? Sn 119 As 75 Some Properties of Selected Elements Element Color Atomic Mass Bonding Power Silicon steel gray 28 4 Gallium* gray-black 70 3 Ekasilicon??? Arsenic silver to gray-black 75 3 Tin gray-white *One of Mendeleev s original missing elements, which was discovered in Which elements would you use to predict the properties of ekasilicon? Why? 2. What color would you expect ekasilicon to be? 3. How many chemical bonds would you expect ekasilicon to form? 4. What atomic mass would you expect ekasilicon to have? Why?

5 Metals Understanding Main Ideas Answer the following questions in the spaces provided. Use a separate sheet of paper if you need more room. Use a periodic table for reference. 1. What physical properties are shared by most metals? 2. Sodium (Na) and calcium (Ca) are in different families of metals. Name the families of metals in which they belong, and describe each family s characteristics. 3. Would a metal in Group 13 be more or less reactive than a metal in Group 1? Explain. 4. In what periods are the lanthanides and actinides? Where are they placed in the periodic table? Why? Building Vocabulary Fill in the blank to complete each statement. 5. The reaction of a metal with oxygen to form rust is called. 6. A material that is can be hammered into thin sheets and other shapes. 7. The ability to transmit heat or electricity to other objects is called. 8. A material that is can be drawn into a wire. 9. is the ease and speed with which an element combines with other substances. 95D

6 Metals Read the passage and look at the tables below it. Then use a separate sheet of paper to answer the questions that follow the tables. More Properties of Metals You have learned that elements in the same group of the periodic table have similar properties. For example, the metals of Group 1 are so reactive they do not exist uncombined in nature. The Group 2 metals are also quite reactive. The tables below show the atomic radius and reactivity of most of the metals in Groups 1 and 2. The more reactive a metal is, the more stars appear in the reactivity column. The tables also give the atomic radius of these elements. You might expect the atomic radius of an element to be half its diameter. However, atoms do not have a definite surface, as a ball does. An atom s electrons are constantly moving around the nucleus in a region of space that has no distinct edge. So, atomic radius is calculated as one half the distance between the nuclei of two identical atoms. The unit of measurement is the picometer (pm). One picometer is equal to meter. Group 1 Group 2 Period Element Atomic Radius (pm) Reactivity Rating Period Element Atomic Radius (pm) Reactivity Rating 2 Li Na K Rb Cs Be 89 3 Mg Ca Sr Ba How does the atomic radius change from top to bottom in Groups 1 and 2? 2. How does the atomic radius change from left to right in Groups 1 and 2? 3. How does reactivity change from top to bottom in Group 1? Does the same pattern hold in Group 2? 4. How does reactivity change from left to right in Groups 1 and 2? 5. What seems to be the relationship between atomic radius and the reactivity of the elements in Group 1 and Group 2? 6. Francium is the Group 1 element of Period 7 and below cesium in the periodic table. Infer how francium s atomic radius compares to cesium s. Do you think francium is more or less reactive than cesium? Explain.

7 Nonmetals and Metalloids Understanding Main Ideas Complete the following table. Use a periodic table for reference. Element Metal, Metalloid, or Nonmetal Family Name Arsenic metalloid 1. Sulfur 2. oxygen family Tin metal 3. Neon 4. noble gas Chlorine nonmetal 5. Silicon 6. carbon family 7. Where in the periodic table are the nonmetals located? Where are the metalloids? Building Vocabulary Fill in the blank to complete each statement. 8. A(n) is formed of two atoms. 9. The are a family of very reactive elements. 10. A type of element that has some of the properties of metals and some of nonmetals is called a(n). 11. The are a family of unreactive elements. 12. A(n) is a type of element whose physical properties are generally opposite to those of metals. 13. A substance that carries electricity under certain circumstances, but not under other circumstances is called a(n). 105D

8 Nonmetals and Metalloids Read the passage and look at the table below it. Then use a separate sheet of paper to answer the questions that follow the table. You may refer to the periodic table. Nonmetals in the Atmosphere On Earth, most nonmetals are found in their uncombined state in the atmosphere. In addition, some nonmetals combine with other nonmetals to form important compounds in the atmosphere. Some of the gases in the atmosphere support life on the planet in one way or another. Others, in great enough concentration, can be dangerous to living things. Composition of Earth s Atmosphere Component Nitrogen (N 2 ) Oxygen (O 2 ) Percent in Air at Sea Level Relationship to Living Things Used by bacteria to produce substances plants can absorb as nutrients; part of all proteins Required for respiration, a process in living things that releases energy Water (H 2 O) 1.0 (avg.) Essential to life as we know it Argon (Ar) 0.93 None known Carbon dioxide (CO 2 ) Neon (Ne) None known Helium (He) None known Nitrous Oxide (N 2 O) Carbon monoxide (CO) Needed by plants to produce their own food through photosynthesis Commonly used as a dental anesthetic but has no effect in concentrations found in the air Poisonous gas produced in part by the burning of fossil fuels 1. Based on this table, what do the Group 18 elements have in common? 2. Which substances are combinations of nonmetals? 3. Which nonmetals in the atmosphere and their combinations are essential to life on Earth? 4. Which are the four most abundant components of the atmosphere? Taken together, about what percent of the atmosphere do those four components make up?