Transcript Mineral Chemistry

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.)