Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Working with the Properties and Changes of Matter A chemical is any substance that has a definite composition. A chemical reaction is the process by which one or more substances change to produce one or more new substances. Section 1 What Is Chemistry? Chapter 1

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Physical States of Matter, continued Properties of the Physical States The states of matter are the physical forms of matter which are solid, liquid, gas, and plasma. Solids have a fixed volume and shape that result from the way their particles are arranged. Liquids have a fixed volume but not a fixed shape. Gases have neither fixed volume nor shape. Section 1 What Is Chemistry? Chapter 1

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Water in Three States Section 1 What Is Chemistry? Chapter 1

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Pure Substances A pure substance is a sample of matter, either a single element or a single compound, that has definite chemical and physical properties. Elements are pure substances that only contain one kind of matter. They cannot be separated or broken down into simpler substances by chemical means. Each element has its own unique set of physical and chemical properties. Section 3 How Is Matter Classified? Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Pure Substances Section 3 How Is Matter Classified? Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Elements are Pure Substances Each elements is represented by a distinct chemical symbol. Section 3 How Is Matter Classified? Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Pure Substances, continued Elements as Single Elements or Molecules A molecule is the smallest unit of a substance that keeps all of the physical and chemical properties of that substance. A molecule usually consists of two or more atoms combined in a definite ratio. Diatomic elements exist as two atoms of the same element joined together. Section 3 How Is Matter Classified? Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Pure Substances, continued Some Elements Have More Than One Form Some elements, such as oxygen, phosphorus, sulfur, and carbon, have many different molecular forms. An allotrope is one of a number of different molecular forms of an element. The properties of allotropes vary widely. Section 3 How Is Matter Classified? Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Pure Substances, continued Some Elements Have More Than One Form, continued Oxygen exists as allotropes. Oxygen gas (O 2 ) is colorless and odorless. Ozone (O 3 ) is toxic and pale blue. Section 3 How Is Matter Classified? Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Pure Substances, continued Compounds are Pure Substances Pure substances that are not elements are compounds. Compounds are composed of more than one kind of atom. example: carbon dioxide (CO 2 ) There may be easier ways of preparing them, but compounds can be made from their elements. Compounds can be broken down into their elements, though often with great difficulty. Section 3 How Is Matter Classified? Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Pure Substances, continued Compounds are Represented by Formulas Because every molecule of a compound is made up of the same kinds of atoms arranged the same way, a compound has characteristic properties and composition. Compounds can be represented by an abbreviation or formula. A formula has subscripts which represent the ratio of different atoms in the compound. example: H 2 O has 2 hydrogen atoms and one oxygen atom Section 3 How Is Matter Classified? Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Pure Substances, continued Compounds are Represented by Formulas, continued Molecular formulas give information only about what makes up a compound. example: the molecular formula for aspirin is C 9 H 8 O 4 A structural formula shows how the atoms are connected This two-dimensional model does not show the molecule’s true shape. Section 3 How Is Matter Classified? Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Pure Substances, continued Compounds are Represented by Formulas, continued A ball-and-stick model shows the distances between atoms and the angles between them in three dimensions. A space-filling model attempts to represent the actual sizes of the atoms and not just their relative positions. A hand-held model can provide more information than models shown on the flat surface of the page. Section 3 How Is Matter Classified? Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Pure Substances, continued Compounds are Represented by Formulas, continued These models convey different information about acetylsalicylic acid (aspirin). Section 3 How Is Matter Classified? Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mixtures A mixture is a combination of two or more substances that are not chemically combined. Air is a mixture of mostly nitrogen and oxygen. All the different gases in air are physically mixed. The proportions of the gases can vary. Water is not a mixture. The H and O atoms are chemically bonded The ratio of H to O atoms is always 2 to 1. Section 3 How Is Matter Classified? Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mixtures, continued Mixtures Can Vary in Composition and Properties The proportion of the materials in a mixture can change. The properties of the mixture may vary. An alloy is a solid mixture. example: An alloy of gold and other metal atoms is stronger than pure gold. 18-karat gold contains 18 grams of gold per 24 grams of alloy. 14-karat gold contains 14 grams of gold per 24 grams of alloy. Section 3 How Is Matter Classified? Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Particle Models for Gold and Gold Alloy Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mixtures, continued Homogenous Mixtures A homogenous mixture describes something that has uniform structure or composition throughout. examples: gasoline, syrup, and air Because any two samples of a homogenous mixture will have the same proportions of ingredients, homogenous mixtures have the same properties throughout. Section 3 How Is Matter Classified? Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mixtures, continued Heterogeneous Mixtures A heterogeneous mixture describes something that is composed of dissimilar components. example: A mixture of sand and water is a heterogenous mixture. Any two samples of a heterogeneous mixture will have the different proportions of ingredients. Heterogeneous mixtures have different properties throughout. Section 3 How Is Matter Classified? Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Examples of Mixtures Mixtures are either homogenous or heterogeneous. Section 3 How Is Matter Classified? Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Types of Mixtures Chapter 2 Section 3 How Is Matter Classified?

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mixtures, continued Distinguishing Mixtures from Compounds The properties of a mixture reflect the properties of the substances it contains. The properties of a compound often are very different from the properties of the elements that make it up. A mixture’s components can be present in varying proportions. A compound has a definite composition in terms of the masses of its elements. Section 3 How Is Matter Classified? Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Classification of Matter Filtration vs. Distillation Filtration uses gravity to separate a solid from a liquid. (heterogeneous) Distillation uses heat to separate liquids using their boiling points. (homogeneous) Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Classifying Matter Chapter 2 Section 3 How Is Matter Classified?

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 1.Which of the following is best classified as a homogeneous mixture? A.blood B.copper wire C.pizza D.hot tea Standardized Test Preparation Understanding Concepts Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 1.Which of the following is best classified as a homogeneous mixture? A.blood B.copper wire C.pizza D.hot tea Standardized Test Preparation Understanding Concepts Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 2.Which of the following statements about compounds is true? F. A compound contains only one element. G.A compound can be classified as either heterogeneous or homogeneous. H.A compound has a defined ratio by mass of the elements that it contains. I.A compound varies in chemical composition depending on the sample size. Standardized Test Preparation Understanding Concepts Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 2.Which of the following statements about compounds is true? F. A compound contains only one element. G. A compound can be classified as either heterogeneous or homogeneous. H. A compound has a defined ratio by mass of the elements that it contains. I. A compound varies in chemical composition depending on the sample size. Standardized Test Preparation Understanding Concepts Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 3.Which of the following is an element? A.BaCl 2 B.CO C.He D.NaOH Standardized Test Preparation Understanding Concepts Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 3.Which of the following is an element? A.BaCl 2 B.CO C.He D.NaOH Standardized Test Preparation Understanding Concepts Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 4.Is photosynthesis, in which light energy is captured by plants to make sugar from carbon dioxide and water, a physical change or a chemical change? Explain your answer. Standardized Test Preparation Understanding Concepts Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 4.Is photosynthesis, in which light energy is captured by plants to make sugar from carbon dioxide and water, a physical change or a chemical change? Explain your answer. Answer: Photosynthesis is a chemical change because the products of the change are different substances than the starting materials. Standardized Test Preparation Understanding Concepts Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 5.A student checks the volume, melting point, and shape of two unlabeled samples of matter and finds that the measurements are identical. He concludes that the samples have the same chemical composition. Is this a valid conclusion? What additional information might be collected to test this conclusion? Standardized Test Preparation Understanding Concepts Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 5.A student checks the volume, melting point, and shape of two unlabeled samples of matter and finds that the measurements are identical. He concludes that the samples have the same chemical composition. Is this a valid conclusion? What additional information might be collected to test this conclusion? Answer: The conclusion is not valid because volume and shape give no information about identity and two different substances can have the same melting point. Additional information could include determining additional physical properties or chemical properties. Standardized Test Preparation Understanding Concepts Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 6.Describe the physical and chemical changes that occur when a pot of water is boiled over a campfire. Standardized Test Preparation Understanding Concepts Chapter 2

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 6.Describe the physical and chemical changes that occur when a pot of water is boiled over a campfire. Answer: A physical change is the conversion of liquid water to vapor. A chemical change is the reaction between wood and oxygen that generates heat while forming carbon dioxide and ash. Standardized Test Preparation Understanding Concepts Chapter 2