2. Chapter: Atoms, Elements, Compounds, and Mixtures Table of Contents Section 3: Compounds and Mixtures Section 1: Models of the Atom Section 2: The Simplest Matter
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36. 1 Section Check Question 1 Explain why early Greek philosophers thought that matter was composed of atoms.
37. 1 Section Check Answer The early Greeks didn’t do experiments; they relied only on reasoning. They reasoned that if you kept cutting something in half, eventually you would have a piece so small it couldn’t be cut any more.
38. 1 Section Check Question 2 The first modern atomic theory was proposed by _______. A. Aristotle B. Dalton C. Rutherford D. Thompson
39. 1 Section Check Answer The answer is B. John Dalton was a 19th century English school teacher. He thought atoms were tiny, hard spheres.
40. 1 Section Check Question 2 A cathode-ray tube has two electrodes, one at either end. These are known as the _______ and the _______.
41. 1 Section Check Answer The answer is cathode and anode. Sometimes a cathode-ray tube is abbreviated to CRT.
57. 2 Section Check Question 1 An element is matter made of only _______ kind of atom. A. one B. two C. three D. four
58. 2 Section Check Answer The answer is A. Aluminum is an example of an element.
59. 2 Section Check Question 2 Chemists organize all the known elements on a particular chart known as the _______. It is called the periodic table of the elements. Not only does the periodic table organize the known elements, it helps predict properties of those that have yet to be discovered. Answer
60. 2 Section Check Question 3 Chlorine-35 has 18 neutrons in its nucleus, while chlorine-37 has 20. How can these both be chlorine atoms?
61. 2 Section Check Answer Chlorine-35 and chlorine-37 are isotopes. Atoms of the same element can have different numbers of neutrons, as long as they have the same number of protons.
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72. Section Check 3 Question 1 A substance whose smallest unit is made up of atoms of more than one element bonded together is a _______. A. compound B. element C. isotope D. mixture
73. Section Check 3 Answer The correct answer is A. An everyday example of a compound Is H 2 O – water.
74. Section Check 3 Question 2 H 2 0 2 is the _______for hydrogen peroxide. It is the chemical formula. Even a small difference in chemical formulas can result in very different substances. Answer
75. Section Check 3 Question 3 Two or more substances that come together without making a new substance form _______. A. allotrope B. element C. mixture D. solution
76. Section Check 3 Answer The answer is C. You can change the proportions of the substances in a mixture without changing the identity of the mixture itself.
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