Chemistry and Minerals

Atoms, Elements and Ions

Atom • is the smallest unit of all substances and

comprised of protons (plus charged) and neutrons (no charge) located in nucleus (center) of atom and electrons (minus charged) which orbit the nucleus

• this structure resembles the solar system with the sun (protons and neutrons) at the center and planets (electrons) orbiting the central portion

Atom

Element– is a substance comprised of atoms each atom

with the same number of protons but not necessarily same number of neutrons and electrons

– there are many different elements (see the Periodic Table of elements)

• Atomic Number of an Element– is the common number of protons in the

nucleus of each atom of the element– examples: 1 proton in each atom of hydrogen

(H) and 92 for the same in uranium (U)

Elements (continued)• Atomic Mass of an Element

– is the sum of the number of protons and neutrons in each atom of an element

– examples: any oxygen (O) atom with an atomic mass of 16 has 8 neutrons and 8 protons in its nucleus and that for uranium (U) with an atomic mass of 235 has 92 protons and 143 neutrons

– the aforementioned atoms will have an atomic mass designation of O16 and U235 respectively

Elements (continued)• Isotope of an Element

– atoms of an element which have the same atomic mass belong to the same element isotope

– stable isotopes are atoms which are not radioactive which means they do not break down or decay to form atoms of other elements

– examples of stable isotopes are O16, O17, and H1

– unstable isotopes are atoms which are radioactive and decay to form atoms of other elements

Elements and Isotopes (continued)

– examples of unstable isotopes are U238, ( which decays to Pb206) and C14(which decays to N14), or any isotope which has an atomic number greater than that for bismuth (Bi)

• Atomic Weight of an Element– is the average of the atomic masses of all the

stable and unstable (radioactive) isotopes of an element

• Periodic Table of Elements– a listing of the elements in order of increasing

atomic number left to right and top to bottom

Periodic Table of Elements

Ion– an ion is a charged atom of an element caused

by the atom having an unequal number of protons and electrons

• Cation– is a + (plus) charged atom resulting from the

number of protons exceeding the number of electrons

– if a sodium (Na) atom with its 11 protons has lost an electron from the original 11, it then has 10 electrons and becomes a cation since there is a sufficiency of + charges over - charges

Ion (continued)• Anion

– is a (-) minus charged atom caused by the number of electrons exceeding the number of protons in the atom

– if a chlorine (Cl) atom with its characteristic 17 protons has acquired an extra electron from the original 17 it has 18 electrons and becomes an anion since it is deficient in the number of protons compared to the number of electrons

Chemical Bonds

Chemical Bonds• are forces which hold atoms together

• the type of bond between atoms can determine mineral properties including physical and chemical properties

• there are three main types of chemical bonds in minerals

Chemical Bonds (contin)• Ionic Bond

– is an attraction between atoms caused by a transfer of electron(s) from one atom to another

– an example is atoms in halite (NaCl); each sodium (Na) atom transfers one electron to a chlorine atom

– this causes each Na atom to become plus charged and each chlorine atom minus charged resulting in an attraction of the atoms

• Covalent Bond– is a force between atoms caused by a sharing

of electron(s) between atoms

Ionic Bond

Covalent Bond

Covalent Bonds (contin)– an example of a covalent bond is in the atoms of

graphite (C) ; each atom of carbon shares electrons with another carbon atoms

– since one carbon atom has all of the shared electrons at one instant it is minus charged while the other atom is deficient in electrons and plus charged

• Metallic Bond– is a force caused by electrons moving freely

between atoms– an example of this is electrons of iron (Fe) atoms

moving between iron atoms

Ionic Bonds (cont)– this flow of electrons results in good electrical

conductivity in substances – often a bond between atoms is a mixture of the

above cited bonds

Minerals

Minerals• Definition

– naturally occurring– inorganic solid substance– having an orderly arrangement of atoms– having a consistent chemical composition that

may vary within specific limits

• Explanations– man made diamonds are not naturally occurring

therefore are not minerals– natural petroleum and coal are referred to as

mineral resources but are organic in composition

Minerals-Explanations (contin)

– ice is a mineral if formed in nature– a mineraloid is a substance which conforms with

1, 2, and 4 above but does not have an orderly arrangement its atoms

– there are two major differences between minerals and rocks:• 1. minerals can have crystal form but rocks

cannot (any mineral can form a crystal shape if it has adequate space in which to grow)

• 2. minerals occur in smaller or limited amounts while rocks occur in large massive amounts

Minerals (contin)• Origin and Occurrence of Minerals

– formed during the rock forming process and comprise an essential part of the rock

– formed in cracks, fractures, or holes within the rock after the formation of the rock

• Mineral Classification– minerals are classified into classes (groups) based on

chemical composition– based primarily on the anion type present in the

mineral– 1. Non-silicate minerals

• Oxides--oxygen (O) is the major mineral anion

Mineral Classes (contin)• with examples as hematite (Fe2O3), and magnetite

(Fe3O4)

• 2. Sulfides--sulfur (S) is the major anion with examples as galena (PbS), pyrite (FeS2), and sphalerite (ZnS)

• 3. Sulfates--sulfur (S) and oxygen (O) together form the major (complex) anion with examples as barite (BaSO4) and gypsum (CaSO4.2H2O)

• 4. Native elements--atoms of one element with examples as mineral sulfur (S), and graphite (C)

• 5. Halides--Cl, Br, F, or I is the major anion with examples as halite (NaCl) and fluorite (CaF2)

Mineral Classes (contin) • 6. Carbonates--carbon (C) and oxygen (O) together

form the major (complex) anion with examples as calcite (CaCO3) and dolomite-CaMg(CO3)2

• page 53 in your text shows a Table of Common Non-silicate Minerals

Mineral Classes (contin)– 2. Silicate Minerals

• Silicon (Si) and oxygen (O) together form the major (complex) anion

• this is the single most abundant class (group) of mineral

• all igneous rocks, most sedimentary rocks and all but one metamorphic rock are comprised of silicate mineral aggregates

• the tetrahedron is the “basic building block” of the silicate mineral structure

• see page 48 for common silicate minerals and structures

Minerals (contin)• Identification of Minerals by Name

– 1. Use of Physical Properties• Color-- colors can differ from one sample to

another of the same mineral • Luster--metallic and nonmetallic • Streak color--color of the powder of a mineral on a

porcelain (streak) plate• Hardness • Cleavage or fracture--a mineral will break apart in a

consistent pattern (cleavage) or it will not and shatter like glass (fracture)

• Other special physical characteristics

Minerals ID by Name (contin)– 2. Use of Chemical Analysis

• The element composition of a mineral gives important information when trying to determine the name of a mineral

– 3. Use of X-ray Analysis• the atomic arrangement in a mineral is like a

genetic code for that mineral and Xray analysis can determine that code

• Radioactivity in Minerals– allows the absolute age of a rock to be determined

Radioact. in Minerals (contin)– some atoms of elements comprising the chemical

makeup of minerals in rocks are radioactive– 1. Radiation Particles in Minerals

• radioactive particles are emitted from the nucleus of atoms when atoms of elements decay to form other elements

• most common are alpha particles (plus charged) ,beta particles (minus charged), and gamma particles (no charge)

– 2. Radioactive Parent and Daughter Isotopes• parent atoms are radioactive and decay eventually to

stable atoms of an element called a daughter

Parents and Daughter (contin)• examples of radioactive parent and stable daughter

isotopes are: U238 and Pb206; K40 and Ar40; C14 and N14

– 3. Absolute Age Determination Method• the amounts (number of atoms) of parent and

daughter are determined by a mass spectrograph--based on the amounts of each the age of the rock can be determined

• in order for the determination to be successful and accurate the minerals in which the daughter and parent atoms occur must be formed at the same time as the rock

Absol. Age Determ. Method (contin)• the amounts of parent and daughter cannot be

externally introduced or extracted from the rock whose age is to be determined

• many sedimentary rocks are comprised of accumulations of mineral or rock particles from previously formed rocks hence the amounts of parent and daughter represent the time of formation of that previously formed rock

• most absolute age determinations are obtained using igneous rocks

• Important Uses of minerals– 1. Gemstones

Gemstones (contin)• is a rare variety of a mineral• possesses a quality of beauty and is usually hard• rubies (red) and sapphires (blue) are gemstone

varieties of corundum• emeralds (green) and aqua marine are gemstones of

beryl• amethyst and cat’s eye are gemstones of quartz

– 2. Elements Extracted from Minerals• barium (Ba) from barite (BaSO4); iron (Fe) from

hematite (Fe2O3); lead (Pb) from galena (PbS); zinc (Zn) from sphalerite (ZnS)

Mineral- Special Uses(contin)– 3. Other Special Uses

• use of graphite in pencils, sulfur in matches, talc as baby powder, etc.