Defining the atom

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Defining the Atom I Atomic Theory A B C D E F All matter is made up of very tiny particles called atoms Atoms of the SAME element are chemically alike The atoms of an element have a definite mass that is characteristic of the element The Atoms of different elements have a different number of protons in their nucleus (so atoms of different elements have different atomic masses) Atoms are not subdivided, created, or destroyed in chemical reactions Sizes of Atoms: Atomic Radius Atoms are about X 10-12 m in size…so cannot be seen (why we call it the atomic “theory”) What makes elements different? II What is an element? The atoms of different elements have a different number of protons in their nucleus An element is a substance that cannot be broken down to any simpler substance; made up of all the same atoms each with the same number of protons in the nucleus Examples: Hydrogen has just one proton in it’s nucleus, Lithium has 3; Berillium has 4; Sodium has 11 The number of protons in the nucleus is called the atomic number! Structure of the Atom III Structure of the Atom: All atoms are composed of subatomic particles called electrons, protons, and neutrons Electrons, protons, and neutrons are different in terms of their mass, electrical charge, and location in the atom IV Protons and neutrons have the same mass, while electrons are much lighter V Protons have a positive charge, neutrons are neutral (no charge) and electrons have a negative charge VI Protons and neutrons are found in the center of an atom (nucleus), while electrons are attracted to the protons on the outside of the nucleus (opposite charges attract) I Minerals • • • • All minerals are made up of single elements or compounds Element = a substance that cannot be broken down to any simpler substance; made up of atoms Atom = smallest part of an element; has all the properties the element has but cannot be seen even with tools Compound = substances consisting of more than one element Minerals - definition Naturally Occurring  synthetic substances are not minerals Inorganic  plant and animal activities (coal, pearls are not minerals) Solids Definite Chemical Composition Crystalline Structure  a crystal is a regular geometric solid shape; reflects the ordered internal arrangement of atoms Definite Set of Physical Properties Physical Properties of Minerals • • • • • • • Can be used to identify minerals! Color Luster Streak Odor Hardness Breakage Pattern – Cleavage – Fracture Color • • Very useful property only for some minerals Not useful for other minerals because: – Many minerals come in multiple colors – One color (such as white) can be seen in many minerals – May be used for some of the obvious minerals that are almost always one color (sulfur = yellow) Quiz cont • A mineral must be a solid (no liquids or gases) • True Quiz cont • Hardness, luster, and streak are physical properties that are useful in identifying minerals • True Quiz cont • Talc is the softest mineral on Moh’s hardness scale while diamond is the hardest • True Quiz cont • Hardness is determined by scratching a mineral across an unglazed porcelain plate • False Hardness is checked by scratching the mineral against a glass plate and then against reference minerals Quiz cont • Cleavage is the ability of a mineral to break along atomic planes of weakness • True Quiz cont • About elements make up most of the minerals found on Earth • True Quiz cont • All minerals exhibit some form of cleavage • False Some minerals display no special planes of weakness and exhibit fracture Quiz continued • The basic building block of the silicate family of minerals is called the silicon-oxygen tetrahedron • TRUE! Quiz cont • There are six components to the definition of a mineral: – Naturally Occurring – Inorganic – Solids – Definite Chemical Composition – Crystalline Structure – Definite Set of Physical Properties • TRUE! How Are Minerals Formed? • Minerals are formed by the process of crystallization as a result of: Cooling and solidification from magma (liquid rock) (ex: olivine, plagioclase feldspar, potassium feldspar) Precipitation from water caused by evaporation, or over-saturation of minerals (ex: halite & calcite) Chemical reactions from pressure and temperature changes within the Earth (ex: talc, muscovite mica) Chemical reactions from hydrothermal solutions (hot water & dissolved ions from 100°C to 300°C) (ex: bornite, chalcopyrite) How Are Minerals Formed? • Minerals are formed by the process of crystallization as a result of: – cooling and solidification from magma (liquid rock) – precipitation from water caused by evaporation, chemical reactions, and temperature changes – rearrangement of atoms in existing minerals subjected to conditions of high temperatures and pressures found deep within the earth Silicon-Oxygen Tetrahedron • • • The tetrahedron is made up of four oxygen atoms packed closely around a silicon atom The tetrahedron continues outward in all directions like legos, and combines with other metal elements to build the different minerals of the silicate family All of the first 18 minerals in your kits are silicates, except for calcite, gypsum, and halite Silicon-Oxygen Tetrahedron • • • • This is a model of the siliconoxygen tetrahedron The white balls represent oxygen atoms The black ball in the center represents the silicon atom Imagine millions of these linked together in 3D Silicon-Oxygen Tetrahedron • • There are many models used to show the silicon-oxygen tetrahedron The way the tetrahedrons are linked and the other elements it binds with will determine all the physical properties of silicate minerals Silicon-Oxygen Tetrahedron • • Silicates include the minerals quartz, feldspar, augite, and hornblende The very different physical properties these minerals exhibit is due to the slightly different chemical formulas and how the siliconoxygen tetrahedron is linked! [...]... light Streak is the color of the mineral in powder form Color, Luster, and Streak Quiz! • Determining the streak of a mineral is done by whacking the mineral with a sledge hammer until it is pulverized • FALSE! Streak is easily determined by rubbing the mineral across an unglazed porcelain plate Color, Luster, and Streak Quiz! • The streak of a mineral will always be the same as the mineral color... reflected off the minerals surface (opal, garnet) The way light reflects off the surface of a mineral (luster) is useful in identifying the mineral Galena definitely has a metallic luster as it looks like polished metal Graphite may display a “sub-metallic” luster, as it looks like dull metal Quartz has a glassy look, which is called a “vitreous” luster Match the luster description with the appropriate...These are all samples of the same mineral! Quartz comes in many colors! These four minerals (and many others) are all white! Is color always a useful physical property for identifying minerals? •NO! • But it sure makes looking at minerals a lot more interesting! Luster Luster • • • • • The way light shines or glares off the surface of minerals Better than color... streak of a mineral, be sure to follow these steps: • • • Hold streak plate carefully with index finger and thumb of one hand Hold streak plate firmly against desk top Rub mineral across plate firmly to powder it Checking streak • • • Be careful not to break off the corners of the streak plate Some streak plates have sharp edges so WATCH OUT! Check the color of the minerals powder to determine streak... bracelet Streak • • • The color of the powder of a mineral obtained by rubbing the sample across an unglazed porcelain plate (called a streak plate) Most minerals display only one color of streak Examples: – Hematite always has a reddish brown streak, no matter what color the sample is – Sulfur has a yellow streak – Sphalerite has a yellow streak – Magnetite has a black streak When checking the streak of a... when it is different than the color of the mineral itself Hardness of Minerals • • • Hardness is the resistance of a mineral to being scratched All minerals are assigned a hardness value from 1 – 10 based upon “Moh’s Hardness Scale” Hardness is one of the most useful properties because: – Resistance of a mineral to being scratched never changes among different samples of the same mineral – Hardness... Scale Diamonds are so prized because they are harder than any other substance, so they are extremely resistant! Hope Diamond Diamond particles that are not used as gemstones can be used in cutting saws, and are able to cut all other industrial materials Hardness - continued… • • • • Hardness is a very useful property, since a mineral’s hardness is constant – it is the main way we can separate “soft”... is the most useful property used to identify a mineral • FALSE! Too many minerals are the same color and many are white, green, black, etc Color, Luster, and Streak Quiz! • Vitreous is a type of non-metallic luster seen on minerals that reflect light as glass does • True! Vitreous is glassy Color, Luster, and Streak Quiz! • The way a mineral reflects light is called streak • FALSE! Luster is the. .. minerals Many types of luster have been described Somewhat subjective Need to familiarize yourself with terms Luster • Metallic – looks like metal in the way the mineral reflects light (Galena or Pyrite) • Non-Metallic – Does not look like polished metal, so other terms are used Types of Non-Metallic Luster • • • • • • Vitreous - glassy, like glass (quartz) Resinous - a dull shine, like a resin (amber,... dull metal Quartz has a glassy look, which is called a “vitreous” luster Match the luster description with the appropriate luster term by writing the correct number next to the term: Luster Term Definitions _Pearly 1 a brilliant glow at certain angles under the light; such as diamond _Dull (Earthy) 2 shines like reflected glass _Vitreous 3 no shine at all even under bright light _Waxy 4 glistens
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