Chapter Three : Properties and Changes

Chapter Three Section One: Properties of Matter Matter is the “stuff” that everything is composed of. It can also be defined as anything that has mass and takes up space (volume) Matter can be divided into pure substances and mixtures based on their compositions.

Pure Substances – any matter that always has exactly the same composition – Examples : Water, Table Sugar and Sodium Hydrogen Carbonate Any sample of a pure substance has the same properties because it has a fixed, uniform composition. Pure Substances can be classified into two categories: elements or compounds

Classification of Matter © 2009, Prentice-Hall, Inc.

Classification of Matter © 2009, Prentice-Hall, Inc.

Classification of Matter © 2009, Prentice-Hall, Inc.

Classification of Matter © 2009, Prentice-Hall, Inc.

Classification of Matter © 2009, Prentice-Hall, Inc.

The classification of matter is summarized below. Prentice Hall © 2007 Chapter One

Elements – Simplest Forms of Matter Elements cannot be broken down into simpler substances An element has a fixed composition because it is made up of only one type of atom The atom is the smallest particle of an element. The atoms of each element differ from the atoms of every other element.

Characteristics of Elements Most elements exist as solids at room temperature (200 C or 680 F) Some elements are gases at room temperature Only two elements (bromine-Br and mercury-Hg) are liquids at 00 C Element symbols consist of either a single letter or two letters. Single element symbols are always capitalized; element symbols consisting of two letters have the first letter capitalized while the second letter is not capitalized (lower case)

Compounds Compounds are made from two or more simpler substances (elements) and can be broken down into those simpler substances The properties of a compound differ from those substances from which it is made The two or more elements composing a compound are always joined in a fixed proportion (H2O) Stopped here 2nd & 5th & 7th period; 16 Sep 2013

1st period stopped here:16 Sep 2013

Capsaicin biosynthetic pathway. Capsaicin biosynthetic pathway. PAL, phenylalanine ammonia lyase; Ca4H, cinnamic acid 4 hydroxylase; Ca3H, coumaric acid 3 hydroxylase; CoMT, caffeic acid O methyltransferase; pAMT, putative amino transferase; CS, capsaicin synthase; KAS, keto acyl synthase. Prasad B C N et al. PNAS 2006;103:13315-13320 ©2006 by National Academy of Sciences

Mixtures The properties of a mixture can vary because the composition of a mixture is not fixed Mixtures are classified by how well the parts of a mixture mix with each other Mixtures can be heterogeneous or homogeneous

Characteristics of Heterogeneous and Homogeneous Mixtures Heterogeneous mixtures are not well mixed. The parts of the mixtures are noticeably different from one another. Examples: Grains of Sand; Mud and Water; Oil and Water Homogeneous mixtures are so well mixed the substances in the mixture cannot be distinguished from one another. Examples: Sweetened Tea; Swimming Pool Water; Stainless Steel Dinnerware

Special Types of Mixtures Certain mixtures are classified according to the size of their largest particles: Solutions; Suspensions; Colloids Solutions – the largest particles are so small that they dissolve in the mixture so they are no longer visible – sugar and water Solutions do not separate into distinct layers over time; solutions cannot be filtered and they remain clear. Suspensions are mixtures which mix in such a way that the particles remain suspended in the liquid for an extended period of time but will eventually separate out. Suspensions can be filtered into their component parts. 8th period stopped here; 17 sep 2013

Colloids contain some particles that are intermediate in size between the small particles of a solution and the larger particles of suspension. Colloids do not separate into layers and cannot be filtered into their different particles. – Examples: Milk; Fog Stopped here 5th, 7th period 17 Sep 2013

2.2 Physical Properties of Matter A physical property is any characteristic of a material that can be observed or measured without changing the composition of the substances in the material. Examples of physical properties are: viscosity, conductivity, malleability, hardness, melting point, boiling point, density

Viscosity – the resistance of a liquid to flow; the greater the viscosity of a liquid the slower the liquid flows – Examples: high viscosity -honey and corn syrup; low viscosity – vinegar and milk Conductivity – the materials ability to allow heat to flow – Examples: all metals are good conductors of heat; wood is a poor conductor of heat Malleability – the ability of a solid to be hammered without shattering ; Examples – most metals can be hammered into different shapes solids which break or shatter when hammered are said to be brittle Examples: ice and glass

Hardness – compares the hardness of two or more materials to each other – which material will scratch another material or be scratched by that material – Example: stainless steel knife scratching a copper sheet Melting and Boiling Points – the temperature at which a substance changes from a solid to a liquid (melting point); the temperature at which a substance boils (boiling point) Density – the ratio of the mass of a substance to its volume (Density(g/cm3 ) = mass(g)/volume(cm3) Density is used to test the purity of a substance

Figure 12

Physical properties are used to identify a material, to choose a material for a specific purpose or to separate the substances in a mixture. Examples: Calculating densities of metals to determine what they are made of using the conductivity rating of materials to determine if they could be used to make pots for cooking Filtration and distillation are two common methods used to separate the parts of a mixture

2.3 Chemical Properties of Matter A chemical property produces a change in the composition of matter; these properties can be observed only when the substances in a sample of matter are changing into different substances – Examples: Flammability – the burning of a material in the presence of oxygen Reactivity - describes how readily a substance combines chemically with other substances

Recognizing Chemical Changes A chemical change occurs when a substance reacts and forms one or more new substances Three common ways to recognize a chemical change: Color change – copper metal changing color; iron metal rusting Production of a gas – mixing baking soda with vinegar produces carbon dioxide gas Formation of a precipitate – a solid forms and separates when two substances are mixed

What Makes a Change Physical or Chemical? A chemical change produces a change in the composition of matter A physical change occurs when some of the characteristics of matter change but the composition of matter remains the same

Separation of Mixtures © 2009, Prentice-Hall, Inc.

Distillation Distillation uses differences in the boiling points of substances to separate a homogeneous mixture into its components. © 2009, Prentice-Hall, Inc.

Filtration In filtration solid substances are separated from liquids and solutions. © 2009, Prentice-Hall, Inc.

Chromatography This technique separates substances on the basis of differences in solubility in a solvent. © 2009, Prentice-Hall, Inc.