States of MatterAnything that has mass and occupies space is matter. The following classification will help define the states in which matter can occur. Solid - rigid substance that retains its shape unless distorted by a forceCrystalline Solid - as above and the structure (distribution of the components) is highly regular and repetitive - long range orderNon-Crystalline Solid - as above but the structure exhibits a short range order - glass is an non crystalline or amorphous solidLiquid - flows and conforms to the shape of its container - short range orderGas - flows easily and expands to fill its container - disordered structureA Mineral:is a crystalline solidis naturally occurringis inorganic - not formed as part of a life process has a fixed chemical composition or a composition that varies over a known extent
Structure of an AtomAll matter is made up of chemical elements, each of which is made up of particles called atoms. A rather crude, but useful, picture of an atom is that of a rigid sphere. The radii of these atoms are a few angstroms (where an angstrom is 10-10 cm. There are 92 so-called naturally occurring elements of which 90 can be detected on Earth at this time. What happened to the "missing 2" will be left for you to think about. These spheres contain a central nucleus which contains two types of particles:protons which carry a positive charge andneutrons which are neutral (no charge)For our purposes we will ignore quarks and other particles that we would encounter if this were a upper level physics course.The atomic number is the number of protons in the nucleus of the atom. The atomic mass number is the number of protons plus neutrons in the nucleus. All atoms of an element have the same number of protons - hence the same atomic number; for example all atoms of hydrogen have one proton in the nucleus. Each element is assigned a symbol - H for hydrogen. You should learn the symbols for the eight most abundant elements in the Earth"s crust
|1s (max = 2) Total = 2||L||2s (max = 2), 2p (max = 6) Total = 8||M||3s (max = 2), 3p (max = 6), 3d (max = 10) Total = 18|
Chemical BondingMost elements in the Earth react to form compounds although there are a few which are stable as elements (gold, for example). There are several "bonding models" which need to be summarized.Ionic Bonding - Element 11 (Sodium) has a single valence electron which can be relatively easily lost as it is relatively far from the positive charges in the nucleus. Oxygen needs (atomic number 8) needs two electrons to give it full s and p subshells. The compound Na2O consists of two Sodium cations and one Oxygen anion. Each Sodium contributes a single electron to the Oxygen giving the Oxygen a charge of -2. This compound is "held together" by ionic bonds.
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Covalent Bonding - Carbon contains 6 electrons and 4 of them are in the outer most level (the L level). Two carbons could bond by sharing their four electrons which would create the full s and p subshells in the L main shell. Covalent bonding involves sharing electrons.Metallic Bonding - Metals are known for their ability to conduct the flow of electrons. Metallic Bonding involves a "smearing out" of the valence electrons of the metal atoms. These electrons are easily displaced.
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van der Waals Bonding The carbon atoms in graphite are covalently bonded to form sheets of carbon atoms. The sheets are held together by weak attractive forces. The Periodic Table provides a framework in which to place thechemical elements so that their similarities are recognized. Look at the properties of Oxygen and Silicon - the two most abundant elements in the Earth"s crust - by clicking on their symbols on the Periodic Table. The recognition that the elements could be arranged in a systematic way so as to emphasize relationships between elements, was a major break through in the history of chemistry. For example, all of the elements in the first column (the alkali metals) have a singleoutermost electron in its outermost sub shell (an s sub shell).All of these elements can lose a single electron forming a cation with a +1 charge. All of the elements in the column on the far right (inert or Nobel gases) have two s electrons and eight p electrons in their outermost level (called the valence level). Note that the Periodic Table has the shape of a distorted "H". The vertical bars (sides of the H) contain the A group elements. The central bar contains the "transition" elements. Down at the bottom of the page are two rows - the "Lanthanides" and the "Actinides". Look to see where these rows fit into the "H". If these rows which shown in proper position the Periodic Table would be less compact.
The Chemical Composition of the Continental CrustEight elements make up about 99% of the weight of the continental crustOxygen ~ 50%Silicon ~ 25%AluminumIronCalciumSodiumMagnesiumPotassium
Mineral StructuresThink about the statement that oxygen occupies 95% of the volume of the Earth"s crust. If oxygens were cubes they could be packed together to fill up space. However, the oxygens are presumed to be spheres and you cannot pack equal sized spheres to fill up all space; some open spaces will remain inside of the framework produced by the oxygens. Other ions fit into these open spaces. In general, these spaces are "regular".
One common type of space is that created when there are three oxygens on the bottom and one on the top. This is called a "tetrahedral void". (A tetrahedron is a regular solid consisting of four faces, each of which is an equilateral triangle.) The larger the ion the larger the preferred site. The coordination number of a cation is the number of nearest neighbor anions. Silicon, with one exception, prefers to "sit" in a tetrahedral void formed by packing Oxygen anions together. Thus, silicon usually has a coordination number of 4. Coordination numbers are used to produce a structural formula. Remember that the subscripts give the number of ions in one formula unit and the numbers above the chemical symbols given the coordination numbers.Quartz4SiO2Stishovite6SiO2Quartz and Stishovite are polymorphs (many forms). They have identical chemical compositions but differ in structure and hence in physical properties. An increase in pressure favors a larger coordination number. Temperature has the reverse effect. If a large meteorite were to impact quartz then stishovite might form (if the pressure were sufficiently high).Other polymorphs are:diamond and graphite (both carbon)calcite and aragonite (both calcium carbonate)
Calcite and aragonite differ in structure in that in calcite each calcium ion is surrounded by 6 nearest neighbor oxygens. This is an octahedral structure. In aragonite each calcium ion is surrounded by 9 nearest neighbor oxygens. Which of these two minerals has the highest density?aragonite calciteIn the definition of a mineral it was noted that a mineral has a fixed composition (like quartz) or a composition that is variable within a limit. Consider the two minerals Forsterite and Fayalite.Forsterite6 4Mg2SiO4Fayalite6 4Fe2SiO4Note that the two minerals differ chemically in that one has Mg (magnesium) and the other Fe (iron). The rest of the chemical formulas are identical. Note that both Mg and Fe sit in 6 fold sites (octahedral). The sizes of these two ions are nearly identical, the charge on both is +2 and the Mg-O and Fe-O bonds are dominately ionic in nature. When such similarities occur the ions may substitute for each other forming a solid solution series. The series between these two end members is called the olivine series. Compositions range from pure Forsterite to pure Fayalite.Not all solid solution series are complete; some exhibit a limited amount of substitution.Almost all of the common minerals we will work with are solid solution series. Quartz is the notable exception.
Classification of MineralsThe broadest classification of the nearly 3,500 known minerals is based on chemical composition. Thus, we recognize Native Elements (individual chemical elements), Carbonates (containing the CO3 group, Silicates (containing Silicon and Oxygen) and other broad chemical groups. Chemically, the silicates are very complicated and not much progress was made in understanding until a structural classification was devised. The most common "structural element" is the silicon/oxygen tetrahedron. The simplest structural class of silicates consists of those compounds (minerals) which consist of isolated single tetrahedra - the Nesosilicates. Tetrahedra can share oxygens between themselves. Two, three and four oxygens per tetrahedron can be shared and in some structures two or more sharing schemes exist. The most common minerals are listed below. (keep in mind that all of these contain Si and O and many also contain Al).MineralStructural TypeComposition
QuestionsUse the section on Properties to help answer the following questions.Distinguish between fracture and cleavageWhat is luster?What is specific gravity? The specific gravity of the continental crust is about 2.7 whereas the specific gravity of the oceanic crust is 3.0. Quartz and Feldspar are the two most abundant minerals in the Earth"s crust. How does this fit with the list of most abundant elements in the Earth"s crust?Continental Crust - Alkali FeldsparOceanic Crust - Plagioclase
HardnessMineralogists usually measure hardness using a relative scale devised by Frederick Mohs. Mohs scale ranges from Talc with a value of 1 to Diamond with a value of 10. Diamond is NOT 10 times harder than Talc. Quartz has a hardness of 7 and Talc has a hardness of 1. Is Quartz seven times harder than Talc? Explain what type of scale Moh"s Scale is and how to use it. How is a diamond "cut"?The following interactive problem is modified from the National Association of Geoscience Teachers.An ionic bonded material consists of anions and cations which exert a force of electrical attraction toward each other. The value of this attraction is proportional to the product of the charges (C) on the two ions divided by the square of the distance between them:Force of Attraction = Ccation*Canion/Distance2We will assume that the cations and anions just "touch" so that the distance is given by the sum of their radii.We will take the absolute value of the calculated force - that is, the force must be a positive number.Cations are positively charged. TrueFalse
|Calcium - Ca||1.00 A||+2||Chlorine - Cl||1.80A||-1||Fluorine - F||1.40A||-1||Magnesium - Mg||0.7A||+2||Sodium - Na||1.00A||+1|