Atoms to Minerals Matter And Atoms Chapter 5 section 1
What is matter? • Matter is anything that has mass and volume. • Mass-the amount of material in a substance • Volume-the amount of space taken up by an object or substance. • Minerals are made of matter because they have mass and volume.
What makes up matter? • Matter is composed of elements. • Element = a substance that cannot be broken into simpler substances by ordinary chemical means. • Ex. oxygen, carbon, nitrogen, hydrogen, silicon, gold • Represented by a symbol (as well as name) • Elements are made of atoms • Atoms are the smallest part of an element that has all the element’s properties
Structure of an Atom • Central region called the nucleus • Consists of protons (positive charges) and neutrons (neutral/no charge) • Most of the mass of an atom • Electrons • Negatively charged particles that orbit around the nucleus • Located in discrete energy levels called shells • Often called an electron “cloud” • In its neutral state, an atom has an equal number of protons and electrons…so, it has no charge.
An Atom Atoms consist mostly of empty space (between the nucleus & its surrounding electrons).
Flattened structure of an atom # protons (+) equals # electrons (-) Electrons in shells Number of outermost electrons determine types of bonding Argon Outermost (Valence) shell
Some definitions: • Atomic number: number of protons in the nucleus (= to the # of electrons in the atom) • Atomic Mass: total mass of protons and neutrons within an atom’s nucleus The # of protons and electrons in an atom determines its properties.
Electrons and Energy Levels • As the # of electrons in atoms increases, more energy levels are needed to hold them. • greatest # of energy levels = 7 • Each level can hold only a specific number of electrons.
Classifying Atoms • The periodic table is a tool used to organize information about the elements. • In rows from left to right # of protons increases • In vertical (up and down) columns, also called groups, elements have similar chemical properties.
Periodic Table of the Elements Shows atomic number (# protons) and atomic mass (# protons + neutrons). Column shows # electrons in outermost shell
Isotopes • The identity of an atom depends on the # of protons. • Elements that have the same # of protons, but a different # of neutrons (and therefore different masses) are called isotopes • Mass # of isotope is equal to the # of protons plus the # of neutrons (mass # = #p + #n) • Often used in geologic dating.
Bonding of Atoms • Most substances on Earth are not pure elements, but rather compounds. • Compounds contain 2 or more elements that are chemically combined • Atoms are most stable when their outermost energy levels are filled (with electrons) • Stable atoms do not readily combine with other elements to form compounds
Bonding of Atoms • Atoms (with shells that are not full) try to fill their outermost shell by gaining, losing, or sharing electrons. • This forms a chemical bond that hold atoms together. • 3 main bond types: • 1. covalent • 2. ionic • 3. metallic
Covalent Bonds • Some compounds form when atoms share electrons. • Two or more atoms held together by covalent bonds form a molecule.
Ionic Bonds • Other compounds are held together by the force of electrical attraction between atoms that have lost or gained electrons. • loses electron positive charge. • gains an electron negative charge. • charged atom is called an ion • Ions with opposite charges attract, forming compounds with ionic bonds. • Common in many minerals
Metals and Nonmetals • Metal = element that loses electrons easily to form positive ions • Ex. sodium, potassium, gold (much of periodic table) • Ionic bonds don’t form between metals • Non-metal = element that gains electrons easily to form negative ions • Ex. chlorine, oxygen, nitrogen (right side of periodic table) • Ionic bonds can form between non-metals • Bonds form easily between metals and nonmetals
Metallic Bonds • Formed between metal atoms • Different characteristics than bonds that form between metal and nonmetal atoms • Electrons move freely around metal ions
Compounds and Mixtures • Compounds • Can have properties unlike those of the elements from which it is made • Elements combine in a fixed proportion • Can only be separated by chemical means (electricity) • Ex. water hydrogen, and oxygen • Ex. salt sodium, and chlorine • Mixtures • Individual elements (or compounds) keep their own properties • Elements/compounds can be present in any proportion • Most can be separated by physical means (evaporation) • Ex. salt water
Composition and Structure of Minerals Chapter 5 Section 2
What is a mineral? …a naturally occurring, solid, inorganic substance that has a definite chemical composition & molecular structure
Mineral Criteria The 5 “must haves” to be classified a MINERAL
1. Naturally Occurring A mineral cannot be man-made!!! It must be formed in nature.
2. Solid Matter • A mineralMUST BE A SOLID(not a liquid or a gas)! • Minerals can be crushed into powder, which is still a solid!
3. Definite Chemical Composition • Each mineral has a chemical composition – a “Recipe” for making that mineral. Change the recipe and you change the mineral!
4. Atoms Arranged in an Orderly Pattern • When the atoms combine, they must form a PATTERN (crystalline structure)
5. INORGANIC • A mineral CANNOT be made from anything that is, was, or will be living! EXCEPTION • Shells are PRODUCED by living things (but the shells themselves are not alive).
Most minerals are compounds(elements combine in a fixed proportion). • Quartz • Compound of silicon and oxygen • Galena • Compound of lead and sulfur • Minerals made of single elements are called native elements. • Silver, copper, sulfur, diamond, graphite
How do minerals form? 1. Solidification of molten materials *atoms, molecules, & ions move closer together & form compounds *minerals that form depend on the types & amounts of elements present *rate of cooling affects size of mineral grains 2.Evaporation of seawater *as water molecules evaporate, dissolved ions bond to form minerals (ex. halite) 3.Transformation by heat, pressure, or chemical action
Structure of Minerals: Crystal Structure • All minerals have CRYSTALLINE STRUCTUrE (internal arrangement of atoms) • **The internal arrangement of atoms affects the mineral’s physical properties, especially shape, hardness and cleavage/fracture.** • repeated in three dimensions halite
Crystal Faces • Some minerals actually form “crystals” (a regular geometric solid with smooth surfaces called crystal faces) • However, there may not be enough room for crystal faces to develop fully, or “grow.” The mineral just fills the available space. • The mineral is still crystalline, but crystal faces are not visible.
Examples Systems 6 Basic Crystal Shapes The angle between crystal faces is characteristic for each type of mineral and can be used in identification.
O2 - O2 - Si4+ O2 - The Silicon-Oxygen Tetrahedron—an example of ionic bonding. O2 - Silicon Oxygen Tetrahedron Animation Silicates Most minerals are composed of only 8 elements! Silicon and oxygen are the two most abundant elements in Earth’s crust. 90+% minerals (and, therefore, rocks) contain these elements.
Crystal Structure & Physical Properties • Minerals are solids due to crystalline structure. • Crystal structure determines a mineral’s cleavage (tendency to split along definite planes). • Cleavage planes correspond to planes of weak bonds between the atoms, ions, or molecules. • The hardness of a mineral also depends on the internal arrangement of atoms. (ex. diamond and graphite)
Example • Diamond and Graphite are both pure carbon, but have different molecular structures.
Identifying Minerals • Mineralogy: the study of minerals and their properties. • Many minerals can be identified & classified by inspecting them visually and performing simple tests to determine their properties. Chapter 5 Section 3
Rock-Forming Minerals Most rock-forming minerals are silicates. Common rock-forming minerals. Clay Quartz Calcite Olivine Dolomite Pyroxene Amphibole Biotite and Muscovite Micas Orthoclase and Plagioclase Feldspars
Identifying Minerals by Inspection Observed properties should be considered together.A mineral is rarely identified by a single property.
Physical Properties of Minerals • Color • Most easily observed property • Some minerals have distinctive colors, but color is generally unreliable for identification because impurities or oxidation (exposure to oxygen in air/water) can change a mineral’s color • Exotic colorations of some minerals produce gemstones. However, we still use color as one of the many properties for mineral identification.
Quartz (SiO2) exhibits a variety of colors. milky quartz citrine amethyst smoky quartz
Luster • The way a mineral’s surface reflects light • “metallic” or “nonmetallic” Nonmetallic luster: Adamantine – brilliant, like a diamond Dull - non-reflective surface Earthy - look of dirt or dried mud Fibrous - the look of fibers/strings Greasy/oily - the look of grease Pearly - the look of a pearl Resinous - the look of resins such as dried glue or chewing gum Silky - the look of silk, similar to fibrous but more compact Vitreous - the look of glass (most common) Waxy - the look of wax
fibrous waxy pearly silky dull greasy/oily earthy adamantine resinous vitreous/glassy Examples of Nonmetallic Luster
Streak • Color of a mineral in its powdered form when it is rubbed on a “streak plate” (unglazed porcelain) • May be same as hand-specimen or different • Helpful in distinguishing different forms of the same mineral • Streaks of nonmetallic minerals are usually colorless or white ALWAYS place streak plate on a flat surface. Never hold it in your hand. It can break and cut you.
Cleavage • Tendency to break along planes of weak bonding • Flat, shiny surfaces (1, 2, 3, 4, 6 common) • Described by resulting geometric shapes • Number of planes • Angles between adjacent planes Cleavage Plane Animation