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Introductory Chemistry: Concepts & Connections 4th Edition by Charles H. Corwin Chapter 4 Matter and Energy Christopher G. Hamaker, Illinois State University, Normal IL © 2005, Prentice Hall Matter • Matter is any substance that has mass and occupies volume. • Matter exists in one of three physical state: – Solid – Liquid – Gas Chapter 4 2 Gaseous State • In a gas, the particles of matter are far apart and uniformly distributed throughout the container. • Gases have an indefinite shape and assume the shape of their container. • Gases can be compressed and have an indefinite volume. • Gases have the most energy of the three states of matter. Chapter 4 3 Liquid State • In a liquid, the particles of matter are loosely packed and are free to move past one another. • Liquids have an indefinite shape and assume the shape of their container. • Liquids cannot be compressed and have a definite volume. • Liquids have less energy than gases but more energy than solids. Chapter 4 4 Solid State • In a solid, the particles of matter are tightly packed together. • Solids have a definite, fixed shape. • Solids cannot be compressed and have a definite volume. • Solids have the least energy of the three states of matter. Chapter 4 5 States of Matter Summary Chapter 4 6 Changes of State • Most substances can exist as either a solid, liquid, or gas. • Water exists as a solid below 0°C; as a liquid between 0°C and 100°C; and as a gas above 100°C. • A substance can change physical states as the temperature changes. Chapter 4 7 Solid/Liquid Phase Changes • When a solid changes to a liquid, the phase change is called melting. • A substance melts as the temperature increases. • When a liquid changes to a solid, the phase change is called freezing. • A substance freezes as the temperature decreases. Chapter 4 8 Liquid/Gas Phase Changes • When a liquid changes to a gas, the phase change is called vaporization. • A substance vaporizes as the temperature increases. • When a gas changes to a liquid, the phase change is called condensation. • A substance condenses as the temperature decreases. Chapter 4 9 Solid/Gas Phase Changes • When a solid changes directly to a gas, the phase change is called sublimation. • A substance sublimes as the temperature increases. • When a gas changes directly to a solid, the phase change is called deposition. • A substance undergoes deposition as the temperature decreases. Chapter 4 10 Summary of Changes of State Chapter 4 11 Classifications of Matter • Matter can be divided into two classes: – Mixtures – Pure Substances • Mixtures are composed of more than one substance and can be physically separated into its component substances. • Pure substances are composed of only one substance and cannot be physically separated. Chapter 4 12 Mixtures • There are two types of mixtures: – Homogeneous Mixtures – Heterogeneous Mixtures • Homogeneous mixtures have uniform properties throughout – Saltwater is a homogeneous mixture • Heterogeneous mixtures do not have uniform properties throughout – Sand and water is a heterogeneous mixture Chapter 4 13 Pure Substances • There are two types of pure substances: – Compounds – Elements • Compounds can be chemically separated into individual elements. – Water is a compound that can be separated into hydrogen and oxygen. • An element cannot be broken down further by chemical reactions. Chapter 4 14 Occurrence of the Elements • There are over 100 elements that occur in nature. 81 of those elements are stable. • Only 10 elements account for 95% of the mass of the Earth’s crust: Chapter 4 15 Elements in the Human Body • Oxygen is the most common element in both the Earth’s crust and in the Human body. • While silicon is the second-most abundant element in the crust, carbon is the second most abundant in the body. Chapter 4 16 Names of the Elements • Each element has a unique name. • Names have several origins: – Hydrogen is derived from Greek – Carbon is derived from Latin – Scandium is named for Scandinavia – Nobelium is named for Alfred Nobel. Chapter 4 17 Element Symbols • Each element is abbreviated using a chemical symbol. • The symbols are 1 or 2 letters long. • Most of the time, the symbol is derived from the name of the element. – C is the symbol for carbon – Cd is the symbol for cadmium • When a symbol has a two letter symbol, the first is capitalized and the second is lower case. Chapter 4 18 Other Element Symbols • For some elements, the chemical symbol is derived from the original Latin name. Gold – Au Sodium – Na Silver – Ag Antimony – Sb Copper – Cu Tin – Sn Mercury – Hg Iron – Fe Potassium – K Tungsten – W Chapter 4 19 Types of Elements • Elements can be divided into three classes: – Metals – Nonmetals – Semimetals or metalloids • Semimetals have properties midway between those of metals and nonmetals Chapter 4 20 Properties of Metals • Metals are typically solids with high melting points and high densities and have a bright, metallic luster. • Metals are good conductors of heat and electricity. • Metals can be hammered into thin sheets and are said to be malleable. • Metals can be drawn into fine wires and are said to be ductile. Chapter 4 21 Properties of Nonmetals • Nonmetals typically have low melting points and low densities and have a dull appearance. • Nonmetals are poor conductors of heat and electricity. • Nonmetals are not malleable or ductile and crush into a powder when hammered. • 11 nonmetals occur naturally in the gaseous state. Chapter 4 22 Periodic Table of the Elements • Each element is assigned a number to identify it. It is called the atomic number. • Hydrogen is 1, Helium is 2, up to Uranium which is 92. • The elements are arranged by atomic number on the periodic table. Chapter 4 23 The Periodic Table Chapter 4 24 Metals, Nonmetals, and Semimetals • Metals are on the left side of the periodic table, nonmetals are on the right side, and the semimetals are in between. Chapter 4 25 Physical States of the Elements • Shown are the physical states of the elements at 25°C on the periodic table. Chapter 4 26 Law of Definite Composition • The law of definite composition states that “Compounds always contain the same elements in a constant proportion by mass”. • Sodium chloride is always 39.3% sodium and 60.7% chlorine by mass, no matter what its source. • Water is always 11.2% hydrogen and 88.8% oxygen by mass. Chapter 4 27 Chemical Formulas • A particle composed of two or more nonmetal atoms is a molecule. • A chemical formula expresses the number and types of atoms in a molecule. • The chemical formula of sulfuric acid is H2SO4. Chapter 4 28 Writing Chemical Formulas • The number of each type of atom in a molecule is indicated with a subscript in a chemical formula. • If there is only one atom of a certain type, no ‘1’ us used. • A molecule of the vitamin niacin has 6 carbon atoms, 6 hydrogen atoms, 2 nitrogen atoms, and 1 oxygen atom. What is the chemical formula? C6H6N2O Chapter 4 29 Interpreting Chemical Formulas • Some chemical formulas use parenthesis to clarify atomic composition. • Antifreeze has chemical formula C2H4(OH)2. There are 2 carbon atoms, 4 hydrogen atoms, and 2 OH units, giving a total of 6 hydrogen atoms and 2 oxygen atoms. • Antifreeze has a total of 10 atoms. Chapter 4 30 Physical & Chemical Properties • A physical property is a characteristic of a pure substance that we can observe without changing its composition. • Physical properties include appearance, melting and boiling point, density, conductivity, and physical state • A chemical property describes the chemical reactions of a pure substance. Chapter 4 31 Chemical & Physical Changes • A physical change is a change where the chemical composition of the substance is not changed. • These include changes in physical state or shape of a pure substance. • A chemical change is a chemical reaction. • The composition of the substances changes during a chemical change. Chapter 4 32 Evidence of a Chemical Change • Gas release (bubbles). • Light or release of heat energy. • Formation of a precipitate. • A permanent color change. Chapter 4 33 Conservation of Mass • Antoine Lavoisier found that the mass of substances before a chemical change was always equal to the mass of substances after a chemical change. • This is the law of conservation of mass. • Matter is not created or destroyed in physical or chemical processes. Chapter 4 34 Conservation of Mass Continued • If 1.0 grams of hydrogen combine with 8.0 grams of oxygen, 9.0 grams of water is produced. • Consequently, 3.0 grams of hydrogen combines with 24.0 grams of oxygen to produce 27.0 grams of water. • If 50.0 grams of water decomposes to produce 45.0 grams of oxygen, how many grams of hydrogen are produced? 50.0 g water – 45.0 g oxygen = 5.0 g hydrogen Chapter 4 35 Potential and Kinetic Energy • Potential energy, PE, is stored energy; it results from position or composition. • Kinetic energy, KE, is the energy matter has as a result of motion. • Energy can be converted between the two types. • A boulder at the top of the hill has potential energy; if you push it down the hill, the potential energy is converted to kinetic energy. Chapter 4 36 KE, Temperature, & State • All substances have kinetic energy no matter what physical state they are in. • Solids have the lowest kinetic energy, and gases have the greatest kinetic energy. • As you increase the temperature of a substance, its kinetic energy increases. Chapter 4 37 Conservation of Energy • Just like matter, energy cannot be created or destroyed but it can converted from one form to another. • This is the law of conservation of energy. • There are six forms of energy: heat, light, electrical, mechanical, chemical, and nuclear. Chapter 4 38 Energy and Chemical Change • In a chemical change, energy is transformed from one form to another. For example: Chapter 4 39 Law of Conservation of Mass and Energy • Mass and energy are related by Einstein’s theory of relativity, E = mc2. • Mass and energy can be interchanged. • The law of conservation of mass and energy states that the total mass and energy of the universe is constant. Chapter 4 40 Conclusions • Matter exists in three physical states: – Solid – Liquid – Gas • Substances can be converted between the three states. • Substances can be mixtures or pure substances. Chapter 4 41 Conclusions Continued • Pure substances can be either compounds or elements. • The elements are arranged in the periodic table. • Each element has a name and a 1 or 2 letter symbol. • Elements are classified as either metals, nonmetals, or semimetals. Chapter 4 42 Conclusions Continued • A physical change is a change in physical state or shape. • A chemical change is a change in the chemical composition of a substance. • Both mass and energy are conserved in chemical and physical changes. Chapter 4 43