Bonding_in_Minerals_F11

Bonding_in_Minerals_F11 - Bonding in Minerals The Glue That...

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1 Bonding in Minerals The Glue That Holds Minerals Together GLY 4200 –Fall, 2011
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2 Types of Bonds Intramolecular Ionic Covalent Metallic Intermolecular Hydrogen Van der Waals
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3 Definition of Bonding A chemical bond is an attraction between atoms brought about by: A sharing of electrons between to atoms or, A complete transfer of electrons When a chemical bond is formed, energy is released Breaking chemical bonds requires energy
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4 Substances Formed by Bonding When two or more atoms of the same element bond together, a molecule is formed – example, hydrogen H 2 When 2 or more atoms of different elements combine together chemically, a compound is formed – example, water H 2 O Most minerals are compounds
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5 Ionic Bonding Ionic bonding is the result of electrostatic attraction between two oppositely charged ions Positive ions are formed from metals (usually) and negative ions are usually formed from non-metals
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6 Halite Halite, NaCl, is a classical example of an ionically bonded substance The sodium donates an electron to chlorine to complete the eight- electron subshell on chlorine
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7 Physical Properties of Ionically Bonded Crystals Ionic bonding is non-directional Ionically bonded minerals may yield ions to solution Moderate hardness Fairly high to very high melting points & boiling points Poor thermal & electrical conductors except near the melting points
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8 Polarization Polarity is the distortion of the electron cloud of one atom by another. A standard example is often hydrogen chloride (HCl)
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9 Does Size Affect Polarizing Power? Yes, and so does electronegativity The greater the electronegativity, the greater the polarizing power So for hydrogen halogen compounds: Bond polarity has a huge hand in determining chemistry
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10 Relative Size of Ions The size mismatch of the anions and cations is of importance also If two ions are similar in size, then they exist quite happily If there is a size mismatch, then is it quite likely that covalent bonding will occur
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11 Size Mismatch NaCl melts at 801°C, strong attraction between particles in solid lattice structure (Ionic bonding likely) AlCl 3 sublimes (goes from solid to gas not via the liquid phase) at 180°C, so there are no strong attractions present (Covalent bonding likely)
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12 Polarizing Cations If the cation is small and highly charged, it has a large polarizing power If the anion is large and has a relatively low charge, then it is said to have a large polarizability In the first case, the anion is being polarized by the cation There will be a significant degree of covalent character to the bond
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13 Non-Existent Compounds There are some ionic compounds that do not exist at all Aluminum carbonate is an example The aluminum 3+ cation is so small and highly polarizing that is completely distorts the large CO 3 2- ion into self-decomposition This leaves instead of Al 2 (CO 3 2- ) 3 , carbon dioxide is driven off, leaving aluminum oxide
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This note was uploaded on 12/12/2011 for the course GLY 4200c taught by Professor Warburton during the Fall '10 term at FAU.

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Bonding_in_Minerals_F11 - Bonding in Minerals The Glue That...

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