MINERALS Smith and Pun Chapter 2 ATOMIC STRUCTURE

Transcription

1 MINERALS Smith and Pun Chapter 2 1 ATOMIC STRUCTURE 2 1

2 ATOMIC STRUCTURE (2) (See Smith and Pun, pages 29-35) ELEMENT: Substance that cannot be broken down into other substances by ordinary chemical methods ATOM: Smallest possible particle of an element that retains the properties of that element 3 ATOMIC STRUCTURE (3) ATOMS COMPOSED OF 3 SUBATOMIC PARTICLES: PROTONS + Charge and Contribute Mass Number of Protons Determines the Atomic Number NEUTRONS No Charge and Contribute Mass Same Size as Protons ELECTRONS - Charge and Contribute Tiny Percentage of Mass Move Rapidly Around Nucleus in Pathways Called Shells or Orbitals 4 2

3 ATOMIC STRUCTURE (4) ISOTOPE: Atoms containing the same number of protons but a different number of neutrons The most common isotope of oxygen (O 2 ) has 8 neutrons; the isotope of O 2 with 10 neutrons is far less abundant. Radioactive isotopes are important in determining the age of rocks. 5 STRUCTURE OF AN ATOM EX: SULFUR ATOMIC NUMBER = 16 TOTAL NUMBER of ELECTRONS = 16 2 INNER SHELL 8, 6 OUTER SHELLS Nucleus 16P 16P 16N 16N 6 3

4 CHEMICAL BONDS Atoms tend to react with other atoms when the outermost shell is only partially filled. Electrons like to be paired. The reactions that occur result in the formation of chemical bonds. 1. COVALENT (see Figure 2.13, page 32) Strongest Atoms share electrons with adjacent atoms 2. IONIC (see Figure 2.12, page 31) 1 atom captures 1 or more electrons of another atom Atom that loses electron (cation) + Atom that gains electron (anion) - 7 CHEMICAL BONDS (2) 3. HYDROGEN BONDS (see Figure 2.15, page 32) Weak bond formed between hydrogen atoms incompounds and strong electronegative atoms in other molecules Hydrogen bonding between ice and water molecules affects the structure of water giving it unique properties 4. van der WAALs BONDS Weak bond formed because electrons are not always distributed equally around atoms or molecules. The irregular distribution of electrons means that a weak negative charge may exist on the side with more electrons, and a weak positive charge on the side with a deficiency of electrons. 8 4

5 Minerals are composed of an ordered array of atoms chemically bonded together to form a particular crystalline structure. POLYMORPH Minerals with the same chemical composition but different physical properties Ex: diamond and graphite (pencil lead) Both are composed of carbon (C) but diamond forms under conditions of very high pressure. Graphite consist of widely spaced sheets of carbon atoms loosely held together. 9 CRYSTAL STRUCTURE OF DIAMOND (see Figure 2.23, page 37) 10 5

6 CRYSTAL STRUCTURE OF GRAPHITE (see Figure 2.23, page 37) 11 MINERAL IDENTIFICATION (see text pages and Table 2.1, page 28) CRYSTAL FORM Are crystal faces well developed? LUSTER Character of light reflected by mineral COLOR STREAK Color of mineral in powdered form HARDNESS Resistance of mineral to scratching CLEAVAGE Tendency to break along smooth planes FRACTURE - Minerals that do not break along cleavage planes, fracture 12 6

7 CLEAVAGE 13 CONCHOIDAL FRACTURE 14 7

8 MINERAL IDENTIFICATION (2) SPECIFIC GRAVITY - Ratio of the weight of a mineral to the weight of an equal volume of water TASTE HCL Carbonates will fizz (CO 2 gas is being formed) 15 MINERAL GROUPS (see Figure 2.24, page 39) Approximately 10 minerals are abundant in earth s crust or common rock forming minerals. Rock forming minerals generally consist of about 8 elements. 2 most abundant elements: Silicon (Si) Oxygen (O) 16 8

9 MAJOR MINERAL GROUPS SILICATES Minerals contain silicon and oxygen As well as 1 or more other elements 17 SILICON OXYGEN TETRAHEDRON 4 OXYGEN 1 SILICON 18 9

10 SILICATE STRUCTURES 3 OXYGEN 1 SILICON 19 SILICATES (see Table 2.2, page 40) FERROMAGNESIAN (DARK) SILICATES OLIVINE PYROXENE GROUP AMPHIBOLES NON-FERROMAGNESIAN (LIGHT) SILICATES MUSCOVITE FELDSPAR QUARTZ BIOTITE GARNET 20 10

11 21 GARNET 22 11

12 ASBESTOS 23 NON-SILICATE MINERALS 1. Carbonates Carbonate ion and 1 or more positive ions Most common carbonates: Calcite (CaCO 3 ) Reacts with hcl Dolomite (CaMg(CO 3 ) 2 ) 2. Other Oxide and Hydroxide Minerals Iron oxides such as hematite (Fe 2 O 3 ) and magnetite (Fe 3 O 4 ) 3. Metallic Minerals Gold (Au) and Copper (Cu) are two examples 24 12

13 KARAT VS. CARAT KARAT PURITY OF GOLD (24 KARATS) CARAT UNIT OF WEIGHT FOR PRECIOUS GEMS 1 CARAT =0.2 GRAMS 25 13