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CHEMISTRY The Central Science 9th Edition Chapter 1 Introduction: Matter & Measurement David P. White Prentice Hall © 2003 Chapter 1 The Study of Chemistry Molecular Perspective of Chemistry • Matter is anything that has mass and occupies space. • Matter ultimately consists of atoms. • Atoms are nature’s building blocks. • Compounds may consist of the same type of atoms or different types of atoms. Prentice Hall © 2003 Chapter 1 The Study of Chemistry Why Study Chemistry? • Chemistry is the study of the composition of matter and the changes that matter undergoes. • Five general types of chemistry: organic, inorganic, biochemistry, analytical, and physical. • CHEMISTRY STUDIES EVERYTHING!! Prentice Hall © 2003 Chapter 1 Classification of Matter Three States of Matter: • Gas, liquid, or solid. • Gases (vapors) have an indefinite shape, indefinite volume, and can be compressed. • Liquids have an indefinite shape, but a definite volume. Liquids are not compressible. • Solids are rigid, having a definite shape and volume. They are not compressible. Prentice Hall © 2003 Chapter 1 Classification of Matter Substances, Elements and Compounds: • Substance: matter having distinct properties and the same composition from sample to sample. Substances can be classified as elements or compounds. • Element: simplest form of matter that has a unique set of properties. Cannot be decomposed. Each element contains a unique kind of atom. Ex.: H or C • Compound: a substance containing two or more elements chemically combined in a fixed proportion and structure. Ex.: NaCl Prentice Hall © 2003 Chapter 1 Law of Constant Composition (c. 1800) • Also called the Law of Definite Proportions. • A given compound always contains exactly the same proportion of elements by mass regardless of the source of the compound. • Example: A molecule of pure water (H2O) always is made up of two hydrogen atoms and one oxygen atom. Prentice Hall © 2003 Chapter 1 Classification of Matter • • • • Pure Substances and Mixtures Mixtures: combinations of different substances. Composition of mixtures can vary from sample to sample. If matter is not uniform throughout, then it is a heterogeneous mixture. Ex.: vegetable soup If matter is uniform throughout, it is homogeneous. Ex.: air. Homogeneous mixtures are called solutions. Solutions can be gaseous, liquid, or solid! Prentice Hall © 2003 Chapter 1 Mixtures, Substances, Compounds • If homogeneous matter can be separated by physical means, then the matter is a mixture. • If homogeneous matter cannot be separated by physical means, then the matter is a pure substance. • If a pure substance can be decomposed into something else, then the substance is a compound. Prentice Hall © 2003 Chapter 1 Classification of Matter • • • • Elements If a pure substance cannot be decomposed into something else, then the substance is an element. Each element is given a unique chemical symbol (one or two letters). Elements are building blocks of matter. The main elements in the human body: CHNOPS! Prentice Hall © 2003 Chapter 1 Properties of Matter Types of properties Physical properties can be measured without changing the identity and composition of a substance. Ex.: color, density, m.p. • Intensive properties do not depend on the amount of substance. Ex.: m.p., b.p., density • Extensive properties depend on the amount of substance present. Ex.: mass, volume Chemical properties describe how a substance reacts to form other substances. Ex: flammability Prentice Hall © 2003 Chapter 1 Changes of Matter Physical and Chemical Changes • When a substance undergoes a physical change, its physical appearance changes, not its composition! Ex. Changes of state (ice melting) • When a substance changes its composition, it undergoes a chemical change. Chemical changes = chemical reactions Ex.: solid iron + gaseous oxygen form solid iron oxide Prentice Hall © 2003 Chapter 1 Properties of Matter Physical and Chemical Changes Prentice Hall © 2003 Chapter 1 Chemical Changes • • • • • Four Clues to Chemical Changes Transfer of energy Change in color Production of gas Formation of a precipitate: solid that forms or settles out from a liquid mixture. But…even with a clue, you cannot be sure of a chemical change! You need to test the composition of the sample before and after to be sure! Prentice Hall © 2003 Chapter 1 Properties of Matter Separation of Mixtures • Mixtures can be separated if their physical properties are different. • Separation is based on differences in physical properties. • Separation by filtration, distillation, chromatography, etc. Prentice Hall © 2003 Chapter 1 Properties of Matter Separation of Mixtures • Homogeneous liquid mixtures can be separated by distillation. • Distillation requires the different liquids to have different boiling points. • In essence, each component of the mixture is boiled and collected. • The lowest boiling fraction is collected first. Prentice Hall © 2003 Chapter 1 Separation of Mixtures Properties of Matter • • • • Separation of Mixtures Chromatography separates mixtures that have different abilities to adhere to solid surfaces. The greater the affinity the component has for the surface (paper) the slower it moves. The greater affinity the component has for the liquid, the faster it moves. Chromatography can be used to separate the different colors of inks in a pen. Prentice Hall © 2003 Chapter 1 Units of Measurement SI Units (Système International d’Unités) • There are two types of units: – fundamental (or base) units; – derived units. Prentice Hall © 2003 Chapter 1 Units of Measurement Prentice Hall © 2003 Chapter 1 Units of Measurement Prefixes in the Metric System Prentice Hall © 2003 Chapter 1 Units of Measurement Derived Units • Derived units are obtained from base SI units. • Example: units of distance Units of velocity = units of time meters = seconds = m/s Prentice Hall © 2003 Chapter 1 Units of Measurement Temperature There are three temperature scales: • Kelvin Scale (Absolute Scale) – Used in science. – Same temperature increment as Celsius scale. – Lowest temperature possible = absolute zero – Absolute zero: 0 K = -273.15 oC. Prentice Hall © 2003 Chapter 1 Units of Measurement Temperature • Celsius Scale – Water freezes at 0 oC and boils at 100 oC. – To convert: K = oC + 273.15. • Fahrenheit Scale freezes at 32 oF and boils at 212 oF. – To convert: _Water 5 ¡C = (¡F - 32 ) 9 Prentice Hall © 2003 9 ¡F = (¡C ) + 32 5 Chapter 1 Units of Measurement Temperature Units of Measurement Density • Used to identify substances. • • • • mass Density = volume Units: g/cm3 or g/mL Density is an intensive property. Density is temperature dependent. Why? Water is different! Prentice Hall © 2003 Chapter 1 Exact and Inexact Numbers • Two kinds of numbers are used in science. • Exact numbers: values are known exactly; values are infinitely precise. Ex: definitions (12 inches = 1 foot), the number 1 in conversion factors, counting numbers • Inexact numbers: values have uncertainty. Ex: all measurements (12.34 cm) Prentice Hall © 2003 Chapter 1 Uncertainty in Measurement • • • • Uncertainty in Measurement All scientific measures are subject to error. These errors are reflected in the number of figures reported for the measurement. Precision and Accuracy Measurements that are close to the “correct” value are accurate. Measurements that are close to each other are precise. Prentice Hall © 2003 Chapter 1 Uncertainty in Measurement Precision and Accuracy Prentice Hall © 2003 Chapter 1 Uncertainty in Measurement Significant Figures • Number of digits reported in a measurement reflect the accuracy of the measurement and the precision of the measuring device. • Significant figures: all the figures known with certainty plus one extra figure. Prentice Hall © 2003 Chapter 1 Uncertainty in Measurement • • • • • Significant Figures Rules Non-zero numbers are always significant. Zeros between non-zero numbers are always significant. Zeros before the first non-zero digit are not significant. (Example: 0.0003 has one significant figure.) Zeros at the end of the number after a decimal point are significant. Zeros at the end of a number with no decimal point are ambiguous (e.g. 10,300 g). Use scientific notation or a decimal to indicate number of significant figures. Prentice Hall © 2003 Chapter 1 Uncertainty in Measurement Significant Figures • Multiplication & Division: report answer to the smallest number of significant figures in the calculation. • Addition & Subtraction: report answer to the smallest number of decimal places in the calculation. Prentice Hall © 2003 Chapter 1