Crystal Structure, Coordination Number & Polyhedra, Pauling's Rules, Bonding- Mineralogy | GEO GIRL

GEO GIRL منتشر شده در تاریخ 1400/02/12

20 هزار بار بازدید - 3 سال پیش - This video covers how atoms

This video covers how atoms and ions are arranged in mineral structures. I go over crystal structures, coordination numbers, types of coordination polyhedron (linear, trigonal, tetrahedral, octahedral, cubic, hexagonal closest packing), how Pauling's rules affect crystal structure (Pauling's rules: the electrostatic valency principle, sharing of polyhedral elements 1 & 2, and the principle of parsimony), covalent vs. ionic vs. metallic vs. van der waals bonds, and ionic substitution / solid solution. The atomic radius of cations and anions that come together to form minerals determines the overal mineral structure. This is because the size of an ion controls how many closest neighbors or neighboring ions it can bond to, aka: its coordination number. The larger the central ion, the higher the coordination number. So how are atoms arranged in minerals? Molecules can be arranged as linear, trigonal planar, square planar, tetrahedral, trigonal bipyramidal, octahedral, cubic, or closest packing polyhedra. These individual coordination polyhedra are repeated throughout the mineral structure giving the mineral a macrostructure or crysal habit dependent on its atomic structure. However, molecular coordination polyhedra can repeat in different ways, for example, silica is a tetrahedral molecule, but silica tetrahedra can be repeated and arranged in a mineral in various ways: typically as chains, sheets, or framework structures. Sheet silicates include minerals such as mica which is why mica minerals are so platy and flaky. Quartz is an example of a framework silicate structure, which is why quartz is so hard and durable. But how are these polyhedra repeated? What types of bonds hold molecules together in minerals? Types of bonds in minerals include covalent, ionic, metallic, & van der waals bonds. Salt is an example of a mineral with ionic bonds, diamond is an example of a mineral with covalent bonds, gold is an example of a mineral with metallic bonds, and graphite is an example of a mineral with van der waals forces. However, minerals can contain multiple types of bonds, for example, ice contains both covalent bonds and hydrogen bonds, which are van der waals bonds. Lastly, I discuss substitution of ions into mineral structures by replacement or insertion into interstitial sites or vacancy sites between ions. Hope you enjoy! ;)

Reference: Chapter 4 in Earth Materials by Cornelis Klein: https://amzn.to/3mnQqcb

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0:00 Common ions in minerals
2:20 how ion size affects mineral structure
4:43 Atomic arrangements (coordination polyhedra)
8:49 Coordination number & polyhedra practice!
9:43 Silicate structures
11:15 Paulings rules
11:51 The coordination principle
13:45 The electrostatic valency principle
16:13 Sharing polyhedral elements I
17:01 Sharing polyhedral elements II
18:14 The principle of parsimony
19:05 Forces that hold crystals together
21:44 Chemical bond types
24:32 Atomic substitution or solid solution
28:21 Upcoming content!
29:04 Bloopers!

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3 سال پیش در تاریخ 1400/02/12 منتشر شده است.

20,012 بـار بازدید شده

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