Elements, Compounds and Mixtures • Matter is anything that takes up space and has mass. • All matter can be classified into three forms: elements, compounds and mixtures.
Element • An element is a substance that cannot be separated into simpler substances by ordinary chemical means. Scientists have identified 109 elements. • Each element has a name and a chemical symbol made up of one or two letters. • The smallest part of an element that has all the properties of that element is an atom.
Molecules • Some elements are made up of atoms that are chemically combined to form molecules. • A molecule is two or more atoms held together by chemical forces.
Atomic Structure • Atoms are made up of three main particles: protons, neutrons and electrons. The center of the atom is called the nucleus. Two different kinds of particles are found in the nucleus. One of these is the proton.the proton is a positively charged particle. The other particle that makes up the nucleus is the neutron. A neutron is a neutral particle.
Compounds • A compound is made of atoms of different elements that are bonded together. Water is a compound. Some compounds are made up of aluminum, magnesium, silicon, oxygen and hydrogen.
Mixtures • Some forms of matter are neither elements nor compounds. Instead they are two or more substances mixed together. Such forms of matter are called mixtures. A mixture is two or more substances physically combined. Most rocks, soil, sea water and air are examples of mixtures. Because the substances that make up a mixture are not chemically combined they can be separated by physical means.
Chemical Formulas • The combinations of chemical symbols that represent atoms are called chemical formulas. • A chemical formula shows that elements that make up a compound. A chemical formula also shows the number of atoms of each element in a molecule or smallest particle of the compound.
Subscripts • Subscripts give the number of atoms of the element in the compound. Subscripts are placed to the lower right of the symbols.
Minerals • A mineral is a naturally occurring, inorganic solid that has a definite chemical composition and crystal structure. In order for a substance to be called a mineral, it must have all of the characteristics described in this definition.
Inorganic • A mineral must be inorganic, or not formed from living thing or the remains of living things.
Solid • A mineral is always a solid. Like all solids, a mineral has a definite volume and shape.
Chemical Composition • A mineral has a definite chemical composition. A mineral may made of a single pure substance, or element, such as gold, copper or sulfur. Most minerals are made of two or more elements chemically combined to form a compound.
Crystal Structure • A mineral’s atoms are arranged in a definite pattern repeated over and over again. Atoms not confined, the repeating pattern of a mineral;s atoms forms a solid called a crystal. A crystal has flat sides that meet in sharp edges and corners. All minerals have a characteristic crystal structure. • There are 2500 different kinds of minerals.
Formation and Composition of Minerals • Many minerals come from magma, the molten rock beneath the Earth’s surface. When magma cools, mineral crystals are formed. How and where magma cools determine the size of the mineral crystals. When magma cools slowly beneath the Earth’s crust, large crystals form. When magma cools rapidly beneath the Earth’s surface, small crystals form.
Crystal Formation • Crystals may also form from compounds dissolved in a liquid such as water.When the liquid evaporates, or changes to a gas, it leaves behind the minerals as crystals. Halite, or rock salt, forms in this way.
Most Abundant Elements • The eight most abundant elements in the Earth’s crust are oxygen, silicon, aluminum, iron, calcium, sodium, potassium and magnesium. There are about 100 common minerals formed from the eight most abundant elements.Of these 100, fewer than 20 are widely distributed and make up almost all the rocks in the Earth’s crust.
Identifying Minerals • Minerals have certain physical properties that can be used to identify them, such as color, luster, hardness, streak, density, crystal shape, and other special properties.
Color • The color of a mineral is an easily observed physical property. Color can be used to identify only those few minerals that always have their own characteristic color, such as malachite which is always green. The mineral azurite is always blue. • Many minerals come in a variety of colors. Some are colorless.Colors can also change.
Luster • The luster of a mineral describes the way a mineral reflects light from its surface. Certain minerals have a metallic luster, such as silver, copper and gold. Minerals that do not reflect light have a nonmetallic luster, and are described by terms like glassy, pearly, dull and silky.
Hardness • The ability of a mineral to resist being scratched is known as its hardness. Hardness is one of the most useful properties for identifying minerals. Friedrich Mohs, a German mineralogist, worked out a scale of hardness for minerals ranging from 1 to 10. The number one is assigned to the softest mineral, talc and 10 is assigned to the mineral, diamond.
Streak • The color of the powder scraped off a mineral when it is rubbed against a hard , rough surface is called its streak. The streak may be different from the color of the mineral. Streak can be observed by rubbing the mineral sample across a piece of unglazed porcelain, which is called the streak plate. A streak plate has a hardness slightly less than 7.
Density • Density is the amount of matter in a given space. The density of a mineral is always the same, no matter what the size of the mineral sample.
Crystal Shape • Minerals have a characteristic crystal shape that results from the way the atoms or molecules come together as the mineral is forming. There are six basic shapes of crystal structures: cubic, hexagonal, orthorhombic, monoclinic, tetragonal and triclinic.
Cleavage and Fracture • The terms cleavage and fracture are used to describe the way a mineral breaks. Cleavage is the tendency of a mineral to split along smooth, definite surfaces. Some minerals, like halite, break into small cubes. Micas cleave along one surface, making layers of thin sheets. Most minerals do not break along smooth lines.
Special Properties • Some minerals can be identified by special properties. Magnetite is naturally magnetic. Fluorite glows under ultraviolet light. Halite tastes salty. Sulfur smells like rotten eggs. Calcite fizzes when hydrochloric acid is added to . Uraninite is radioactive.
Ores • The term ores is used to describe minerals or combinations of minerals from which metals and nonmetals can be removed in usable amounts.
Metals • Metals are elements that have shiny surfaces and are able to conduct electricity and heat. Metals can be pressed or hammered into thin sheets and other shapes without breaking. Metals cans also be pulled into thin strands. Iron, lead, aluminum, copper, silver and gold are examples of metals.
Smelting • Most metals are found combined with other substances in ores. After the ores are removed from the Earth by mining, the metals must be removed from the ores. During a process, called smelting, an ore is heated in such a way that the metal can be separated from it. Metals are useful. Copper is used in pipes and electrical wire.
Nonmetals • Nonmetals are elements that have dull surfaces and are poor conductors of electricity and heat. Nonmetals are not easily shaped. Some are removed from the Earth in usable form. Others must be processed. Sulfur,a nonmetal, is used to make matches, fertilizers and medicines.
Gemstones • Gemstones are minerals that are hard, beautiful and durable and can be cut and polished for jewelry and decoration. Once a gemstone is cut and polished, it is called a gem. The rarest and most valuable gemstone- diamonds, rubies, sapphires and emeralds, are known as precious stones. All other gemstones, amethysts, zircons, garnets, are known as semiprecious stones.
Rocks • A rock is a hard substance composed of one or more minerals. A rock can also be made of or contain naturally occurring substances that do not perfectly fit the definition of a mineral. Rocks can be composed of volcanic glass or of opal. Both of these substances lack a crystalline structure.
Types of Rocks • Geologists place rocks into three groups according to how they form: igneous, sedimentary and metamorphic.
Igneous Rocks • Igneous rocks were originally hot, fluid magma within the Earth. Igneous get their name from the Latin word, ignis, which means “fire”.
Sedimentary Rock • Most sedimentary rocks are formed from particles that have been carried along and deposited by wind and water. These particles, sediments or detritus, include bits of rock in the form of mud, sand or pebbles. Sediments also include shells, bones, leaves, stems and other remains of living things. Over time they are pressed together to form rocks.
Detrital • The rocks that form by cementation or compaction are known as detrital or clastic sedimentary rocks. • They are further subdivided by size of the particles.
Chemical Sedimentary • Chemical sedimentary rocks form from solution • An example would be rock salt or gypsum.
Organic Sedimentary • These sedimentary rocks form from the remains of once living organisms or the processes of living organisms. • Coal is an organic rock formed from plants. • Coquina or chalk from from sea creatures.