Ch_02_Lecture_2[1]

Ch_02_Lecture_2[1] - Chapter 2 The Chemical Basis of...

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1 Chapter 2 The Chemical Basis of Life (Continued)
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2 + + + 2 2 2 Protons Neutrons Electrons Mass number = 4 + + 2e Electron cloud Nucleus 0 Figure 2.4A particles mass charge a. proton 1 +1 b. electron ~0 -1 c. neutron 1 0 Composition of an atom e.g., Helium electrons : in various orbital (shells) nucleus protons neutrons
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3 Electrons in an atom Are arranged in shells, which may contain different numbers of electrons 0 Hydrogen (H) Atomic number = 1 Electron Carbon (C) Atomic number = 6 Nitrogen (N) Atomic number = 7 Oxygen (O) Atomic number = 8 Outermost electron shell (can hold 8 electrons) First electron shell (can hold 2 electrons) Figure 2.6 Electron arrangement 2.6 What determines the chemical properties of an atom?
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4 Atoms whose shells are not full Tend to interact with other atoms and gain, lose, or share electrons These interactions Form chemical bonds 0 1. covalent bonds: e.g., H 2 Two major chemical bonds to build compounds: 2. ionic bonds: e.g., NaCl 1. the resulting compound is electrically neutral Two rules are satisfied: 2. outer electron orbits are filled
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5 2.7 Ionic bonds are attractions between ions of opposite charge When atoms gain or lose electrons ( outer shell) Charged atoms called ions are created 0 Transfer of electron Na Sodium atom Cl Chlorine atom Na + Sodium ion Cl Chloride ion Sodium chloride (NaCl) Na Cl Cl Na + Figure 2.7A When an atom loses an electron positive ion cation When an atom gains an electron negative ion anion
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6 An electrical attraction between ions with opposite charges Results in an ionic bond 0
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7 Sodium and chloride ions Bond to form sodium chloride, common table salt 0 Na + Cl Figure 2.7B
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8 2.8
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