chem slide 2 - Chemistry 107: General Chemistry Chemistry...

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Chapter 2 1 Chemistry 107: General Chemistry Chemistry 107: General Chemistry for Engineers for Engineers Prof. Jerry Keister
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Chapter 2 2 Atoms, Molecules, and Ions Atoms, Molecules, and Ions Chapter 2 Chapter 2
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Chapter 2 3 Law of constant composition: Any sample of a pure compound always contains the same mass ratios of each element (because the ratios of atoms of the elements are always the same). John Dalton: Each element is composed of atoms All atoms of an element are identical (actually can have different masses). Compounds are formed when atoms of more than one element combine. In chemical reactions, the atoms are not changed, only the ways in which they are combined. The Atomic Theory of Matter The Atomic Theory of Matter
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Chapter 2 4 The atom consists of positive, negative, and neutral entities ( protons , electrons , and neutrons ). Protons and neutrons are located in the nucleus of the atom, which is small. Most of the mass of the atom is due to the nucleus. There can be a variable number of neutrons for the same number of protons. Isotopes have the same number of protons but different numbers of neutrons. Electrons are located outside of the nucleus. Most of the volume of the atom is due to electrons. The Modern View of Atomic Structure The Modern View of Atomic Structure
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Chapter 2 5 The Modern View of Atomic Structure The Modern View of Atomic Structure 1 Å (Angstrom) = 10 -10 m
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Chapter 2 6 The Modern View of Atomic Structure The Modern View of Atomic Structure
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Chapter 2 7 Isotopes, Atomic Numbers, and Mass Numbers Isotopes, Atomic Numbers, and Mass Numbers Atomic number (Z) = number of protons in the nucleus. Mass number (A) = total number of nucleons in the nucleus (i.e., protons and neutrons). By convention, for element X, we write Isotopes have the same Z but different A. The Modern View of Atomic Structure The Modern View of Atomic Structure X A Z
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Chapter 2 8 Atomic mass unit (amu) - exactly 1/12th the mass of an atom of 12 C. 1 amu = 1.66054 × 10 –24 g. Isotopic mass – the mass of an atom in atomic mass units. Numerically close to the atom’s mass number. Atomic mass values are weighted averages for the naturally occurring mixtures of different isotopes. Atomic mass of an element = Σ (mass of each isotope × the fraction of the isotope). Σ is used for the term “the sum of.”
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Chapter 2 9 Isotopes, Atomic Numbers, and Mass Numbers Isotopes, Atomic Numbers, and Mass Numbers The Modern View of Atomic Structure The Modern View of Atomic Structure
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Chapter 2 10 Average Atomic Mass Average Atomic Mass Relative atomic mass: average masses of isotopes: Naturally occurring C: 98.892 % 12 C + 1.108 % 13 C. Average mass of C: Example of equation on slide 8 - ( 0.98892 )(12 amu) + ( 0.01108 )(13.00335) = 12.011 amu. Atomic weight (AW) is also known as average atomic
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This note was uploaded on 12/08/2011 for the course CHEMISTRY 101 taught by Professor Churchill during the Spring '09 term at SUNY Buffalo.

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chem slide 2 - Chemistry 107: General Chemistry Chemistry...

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