Chem Chapter 2

Chem Chapter 2 - Chapter 2 Atoms, Molecules and Ions...

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Chapter 2 Atoms, Molecules and Ions
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Fundamental Chemical Laws 1. Law of conservation of mass (Lavoisier): ± Mass is neither created nor destroyed. 2. Law of definite proportion (Proust): ± A given compound always contains exactly the same proportion of elements by mass. 3. Law of multiple proportions (Dalton): ± When two elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers.
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Early Atomic Theory Dalton (1808) 1. Each element is made up of tiny particles called atoms. 2. The atoms of a given element are identical. The atoms of different elements are different in some fundamental way.
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Early Atomic Theory 3. Chemical compounds are formed when atoms of different elements combine with each other. A given compound always has the same relative numbers and types of atoms . 4. Chemical reactions involve reorganization of the atoms . The atoms themselves are not changed in a chemical reaction. But there are changes in the way they are bound together.
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J. J. Thomson (1898—1903) Postulated the existence of electrons using cathode-ray tubes . The atom must also contain positive particles that balance exactly the negative charge carried by particles that we now call electrons. Plum Pudding Model Cathode-Ray Tube
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Ernest Rutherford (1911) Explained the nuclear atom . Atom has a dense center of positive charge called the nucleus. Electrons travel around the nucleus at a relatively large distance.
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Modern View of Atomic Structure The atom contains: ± Nucleus ± Electrons – outside the nucleus; (-) charged. The nucleus contains: ± Protons – (+) charged; equal in magnitude to the electron’s negative charge. ± Neutrons – no charge; virtually same mass as a proton.
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Nucleus is very small Accounts for almost all of the mass of an atom High density Density = Mass/Volume The Size of an Atom The radius (electron) >10 5 x radius (nucleus)
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The Size of an Atom Mass of an atom is due to its Protons and Neutrons Size of an atom is due to its Electrons Mass of proton = mass of neutron = 1.66 x 10 -24 g Mass of electron = 9.109 x 10 -28 g Electron <<< Proton, Neutron
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The Charge of an Atom An atom is neutral It has no net charge Number of electrons = number of protons Proton: +1 Neutron: no charge Electron: -1
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Elements and Compounds An Element Made up of only 1 type of atom Lead: Carbon A Compound 2 or more specific atoms (elements) combined in a fixed ratio NaCl: Sodium and Chloride
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Why are atoms different? If all atoms are composed of these same components, why
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Chem Chapter 2 - Chapter 2 Atoms, Molecules and Ions...

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