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Mineral Chemistry GY111 Physical Geology Atoms & Atomic Particles • An atom is the smallest component of an element that can retain the properties of that element • Atoms are composed of fundamental particles: – Protons – Neutrons – Electrons • Protons & Neutrons always reside in the center of the atom termed the nucleus • Electrons are always located in the electron cloud (orbitals) where they orbit the nucleus Example Atom: Carbon • Carbon: contains 6 protons and 6 neutrons in the nucleus, and 6 electrons in 2 orbital shells Subatomic Particles • • • • Proton: has a mass of 1 and a positive charge Neutron: has a mass of 1 and a neutral charge Electron: has a mass of 0 and a negative charge All elements in the periodic table can be considered to have a neutral charge in their elemental form, therefore, they must have the same number of protons and electrons Periodic Table of the Elements • Elements are identified by their atomic number (ex. Carbon = 6) Atomic Number & Weight • Atomic Number: the sum of the protons in the atom; The number uniquely identifies the element. • Atomic Mass: the sum of the protons and neutrons in the nucleus of the atom • Isotope number: same as atomic mass, – C12: 6 protons and 6 neutrons in nucleus – C14: 6 protons and 8 neutrons in nucleus Ions • When an atom in its elemental state receives or gives up one or more electrons it is then termed an “Ion” • Positively charged ions are cations • Negatively charged ions are anions • The ability to give up or take on electrons in an atom is dependent on the atomic number (i.e. the number of electrons in the electron shells) Electron Shell Configurations • The first 3 electron shells are filled by 2, 8 and 8 electrons. • A specific element is chemically stable when its outermost shell is completely filled by electrons • In the below Carbon example the outer shell needs 8 electrons but Carbon has only 4 in the outermost shell because of its atomic number of 6 (2 electrons in the 1st shell, 4 in the 2nd) • Therefore Carbon will either have a +4 ionic charge if it gives up all the outer shell electrons, or a -4 charge if it receives 4 to fill the outer shell Relationship of Electron Shells to Periodic Table • • • • The elements on the Periodic Table are arranged in columns of like electron shell configuration Example: The Alkali Earth metals (H, Li, Na, K, etc.) all have one electron in the outer shell Example: The Halogens (F, Cl, Br, etc.) all have 7 electrons in the outer most shell The Alkalis all tend to form +1 charged cations when bonding with other elements; The Halogens then to form -1 anions Chemical Bonding • Ionic: loss or gain of electrons forming cations and anions (allows material to dissolve in a polar solvent such as H2O) • Covalent: electron sharing in outer shell (strongest bond) • Metallic: electron sharing in inner shell (allows for conduction of electricity) Ionic Bonding Example • NaCl: note that Na (atomic number=11) will form a +1 cation, and that Cl (atomic number=17) will form a -1 anion. Covalent Bonding Example • Diamond has strong covalent bonding in all direction by sharing electrons in the outer shell of each Carbon atom Metallic Bonding Example • Gold (Au) is the best conductor of electricity because of its metallic bonding Common Rock Forming Cations and Anions • Cations: positively charged • Anions: negatively charged • Ionic Radius: size of the charged ion Mineral • Solid: cannot be liquid or gas. • Inorganic: cannot be composed of living or once-living material. • Naturally Occurring: cannot be man-made. • Crystalline: possesses an ordered internal structure and a definite chemical composition. Rock Forming Minerals • • • Silicates: contain Si and O plus other rock forming elements Fundamental structure is SiO4 tetrahedron The geometry of how the tetrahedrons link controls the properties of the silicate mineral Other Major Rock Forming Mineral Groups • • • • • Carbonates: CaCO3 (calcite) Oxides: Fe3O4 (magnetite) Sulfides: FeS2 (pyrite) Sulfates: CaSO4 (anhydrite) Halides: CaF2 (Fluorite) Physical Properties of Minerals • Hardness • Cleavage (Fracture) • Luster (Metallic vs. Non-metallic) – – – – – – Vitreous: glassy Resinous: like tree sap Greasy: oily Pearly: like pearls Silky: like silk Adamantine: luster of diamond • Color • Specific Gravity • Crystal Form (Habit) Moh’s Hardness Scale • Scale allows for the determination of the hardness of a mineral Summary • For Exams know – Definitions of ion, cation, anion – Definitions and examples of ionic, covalent and metallic bonding – Silicate structures and examples (i.e. isolated tetrahedra=olivine, chain=pyroxene, etc.) – Chemical groups of rock-forming minerals and an example of each (Silicates=quartz, Carbonates=calcite; sulfides=pyrite, etc.) – Moh’s Hardness scale – Definition of physical properties of minerals (color, hardness, streak, etc.)