111-5 - GY 111 Lecture Notes D Haywick(2007-08 1 GY 111...

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GY 111 Lecture Notes D. Haywick (2007-08) 1 1 GY 111 Lecture Note Series Bonding and Packing in Minerals Lecture Goals: A) Bonding B) Packing of atoms/ions in crystals Reference: Press et al. (2003), Chapter 3; Grotzinger et al. (2007) Chapter 3 A) Bonding Last time we met, we were discussing basic chemistry. This was necessary in order to examine the chemical characteristics of the mineral groups. Chemical reactions are largely driven by movements of electrons between different atoms. Ions result when electrons are gained ( anions ) or lost ( cations ) during these reactions. Ions are different sizes than their parent atoms. In general, atoms that become cations become smaller and atoms that become anions become larger. The size of the ions/atoms is one of the principle factors regulating how crystals form. I am jumping ahead just now. Let’s get back to the first topic of today; chemical bonding . There are 3 major types of chemical bonds that “glue” together atoms and ions in minerals: 1) Ionic bonding , 2) covalent bonding and 3) metallic bonding . A 4 th type, van der waal or hydrogen bonding, is relatively weak but does play an important role in some of the minerals (e.g., the micas). Ionic bonding is electromagnetic and occurs when ions bond together (consider this a bond resulting from the exchange of electrons ). Remember the mineral halite from last time? This mineral is composed of Na + and Cl - and the resulting ionic bond is very strong because of the charge difference between the two ions. Other minerals characterized by ionic bonding include fluorite, calcite and many others. Covalent bonding is another very strong type of chemical bond. This type, electrons are shared between 2 or more ions . The classic examples illustrating this type of bonding are the molecules H 2 and O 2 (hydrogen gas and oxygen gas).
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GY 111 Lecture Notes D. Haywick (2007-08) 2 2 Many of the sulfide and silicate minerals display covalent bonding. A very simple (and largely incorrect) way to view the covalent bonding in silicate minerals like quartz is as follows: The third type of bonding (metallic) is relatively weak. As the name applies, it is characteristic of metals such as gold, silver and copper. It also occurs in several other types of native elements, most of which you will not see in GY 111. In metallic bonding, there is free movement of electrons around atomic nuclei and it is this property that makes most metals conduct electricity. To explain how the electrons were associated with the nuclei, my High School chemistry teacher asked us to first imagine a pipe packed with gumballs (the atomic nuclei), and then to imagine sugar (electrons) passing through the spaces between the gumballs. Once again, the analogy isn’t all that accurate, but it
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This note was uploaded on 02/04/2012 for the course GLY 111 taught by Professor Haywick during the Fall '11 term at S. Alabama.

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111-5 - GY 111 Lecture Notes D Haywick(2007-08 1 GY 111...

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