Ch2 - CHAPTER 2 ATOMS, MOLECULES, AND IONS Questions 16....

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24 CHAPTER 2 ATOMS, MOLECULES, AND IONS Questions 16. Some elements exist as molecular substances. That is, hydrogen normally exists as H 2 molecules, not single hydrogen atoms. The same is true for N 2 , O 2 , F 2 , Cl 2 , etc. 17. A compound will always contain the same numbers (and types) of atoms. A given amount of hydrogen will react only with a specific amount of oxygen. Any excess oxygen will remain unreacted. 18. The halogens have a high affinity for electrons, and one important way they react is to form anions of the type X . The alkali metals tend to give up electrons easily and in most of their compounds exist as M + cations. Note : These two very reactive groups are only one electron away (in the periodic table) from the least reactive family of elements, the noble gases. 19. Law of conservation of mass: Mass is neither created nor destroyed. The total mass before a chemical reaction always equals the total mass after a chemical reaction. Law of definite proportion: A given compound always contains exactly the same proportion of elements by mass. For example, water is always 1 g H for every 8 g oxygen. Law of multiple proportions: When two elements form a series of compounds, the ratios of the mass of the second element that combine with 1 g of the first element always can be reduced to small whole numbers: For CO 2 and CO discussed in Section 2.2, the mass ratios of oxygen that react with 1 g carbon in each compound are in a 2 : 1 ratio. 20. a. The smaller parts are electrons and the nucleus. The nucleus is broken down into protons and neutrons, which can be broken down into quarks. For our purpose, electrons, neutrons, and protons are the key smaller parts of an atom. b. All atoms of hydrogen have 1 proton in the nucleus. Different isotopes of hydrogen have 0, 1, or 2 neutrons in the nucleus. Because we are talking about atoms, this implies a neutral charge, which dictates 1 electron present for all hydrogen atoms. If charged ions were included, then different ions/atoms of H could have different numbers of electrons. c. Hydrogen atoms always have 1 proton in the nucleus, and helium atoms always have 2 protons in the nucleus. The number of neutrons can be the same for a hydrogen atom and a helium atom. Tritium ( 3 H) and 4 He both have 2 neutrons. Assuming neutral atoms, then the number of electrons will be 1 for hydrogen and 2 for helium. d. Water (H 2 O) is always 1 g hydrogen for every 8 g of O present, whereas H 2 O 2 is always 1 g hydrogen for every 16 g of O present. These are distinctly different compounds, each with its own unique relative number and types of atoms present.
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CHAPTER 2 ATOMS, MOLECULES, AND IONS 25 e. A chemical equation involves a reorganization of the atoms. Bonds are broken between atoms in the reactants, and new bonds are formed in the products. The number and types of atoms between reactants and products do not change. Because atoms are conserved in a chemical reaction, mass is also conserved. 21.
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This note was uploaded on 07/07/2010 for the course CHEM 11 taught by Professor Scholefield during the Summer '08 term at Santa Monica.

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Ch2 - CHAPTER 2 ATOMS, MOLECULES, AND IONS Questions 16....

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