Chapter 2: Matter and Change

Section 2.1 Properties of Matter Objectives: Identify properties of matter as extensive or intensive Define physical property, and list several common physical properties of substances Differentiate among three states of matter Describe a physical change

Matter Matter is anything that has mass and takes up space Mass Volume Measure of the amount of “stuff” (or material) the object contains Don’t not confuse mass with weight Volume Measure of the space occupied by the object

Describing Matter Understanding matter begins with observations… What you observe when you look at a sample of matter is its properties Properties are words that describe matter (adjectives) Substance Matter that has a uniform and definite composition

Describing Matter Properties used to describe matter can be classified as: Extensive – depends on the amount of matter in the sample -Examples: Mass, volume, calories Intensive – depends on the type of matter, not the amount present - Examples: Hardness, density, boiling point

Describing Matter Properties of matter can also be classified as: Physical properties – a property that can be observed and measured without changing the materials composition Examples: color, hardness, melting point, boiling point Chemical properties – a property that can only be observed by changing the composition of the material Examples: ability to burn, decompose, ferment, react with other substances

States of Matter Three Main Phases Look at the pictures at the bottom of your notes page: Shape? Volume? “closeness” of molecules? Three Main Phases

States of Matter There are 3 states of matter Solid Liquid Gas Look at the pictures at the bottom of your notes page: Shape? Volume? “closeness” of molecules? There are 3 states of matter Solid Has a definite shape and volume Particles are packed tightly together Liquid Has indefinite shape, takes shape of container, has definite volume Particles are close together but are free to flow past one another Gas Takes both shape and volume of container Particles are far apart and can move freely Vapor – a substance that is currently a gas, but normally is a liquid at room temperature (water gas? or water vapor?)

States of Matter Three phases of matter

Physical versus Chemical Change Physical Change Changes the appearance of the substance without changing the composition of the material Examples: boil, melt, cut, bend, split, crack Can be both reversible or irreversible Reversible changes involve a change from one state to another (boil, melt) Irreversible – cutting hair, cracking an egg

Physical versus Chemical Change Reversible physical changes

Physical versus Chemical Change A change where a new form of matter is created Examples – rust, burn, decompose, ferment

Section 2.2 Mixtures Objectives Categorize a sample of matter as a substance or a mixture Distinguish between homogeneous and heterogeneous samples of matter Describe two ways that components of mixtures can be separated

Substance versus Mixture Matter that has a uniform and definite composition Mixture A physical blend of two or more components. Mixtures have variable compositions

Classifying Mixtures Mixtures can be classified as: Heterogeneous The mixture is not uniform in composition Examples: gravel, soil, salad, chocolate chip cookie Homogeneous The mixture has a uniform composition throughout Called solutions Examples: iced-tea, salt water Most are liquids, some gases (air), some solids (stainless steel)

Classifying Mixtures Phase? The term phase is used to describe any part of a sample with uniform composition and properties A homogeneous mixture consists of one phase A heterogeneous mixture consists of two or more phases

Classifying Mixtures Olive oil and vinegar are homogeneous mixtures. The substances in these mixtures are evenly distributed. When olive oil is mixed with vinegar, they form a heterogeneous mixture with two distinct phases

Separating Mixtures Some mixtures can be easily separated Rocks and marbles, iron and sulfur (iron is magnetic) Differences in physical properties are used to separate mixtures

Separating Mixtures Filtration Separates a solid from a liquid in a heterogeneous mixture by size Pasta in a colander Water in a coffee filter

Separating Mixtures Distillation A way to separate homogenous mixtures A liquid is boiled to produce vapor that is then condensed into a liquid

Separating Mixtures Distillation What can you infer about the boiling points of the substances in the original mixture?

Section 2.3 Elements and Compounds Objectives Explain the differences between an element and a compound Distinguish between a substance and a mixture Identify the chemical symbol of elements and name elements given their symbol

Distinguishing Elements and Compounds Substances Elements Simplest kind of matter Cannot be broken down into anything simpler All one kind of atom Compound Substance that contains 2 or more elements chemically combined in a fixed proportion When broken down the pieces have completely different properties than the original compound

Distinguishing Compounds from Mixtures Compound or Mixture? Compound Mixture Made of one kind of material Made of more than one kind of material Made by a chemical change Made by a physical change Variable Composition Definite Composition

Breaking down Compounds Compounds can be broken down into simpler substances by chemical means, but elements can not A chemical change is a change that produces matter with a different composition than the original matter Example – sugar is composed of C, H, and O heating sugar will break it down into carbon and water vapor but the carbon will never be broken down further

Properties of Compounds Compounds have very different properties than their component elements Due to a chemical change the resulting compound has new and different properties Example – sodium chloride sodium is a soft gray metal chlorine is a yellow-green poisonous gas sodium chloride is … table salt

Distinguishing Substances and Mixtures If the composition of a material is fixed, the material is a substance If the composition of a material varies, the material is a mixture Examples Premium, plus and regular gas – Whole, 2%, 1% and skim milk – Carbon dioxide – - always 1 carbon for every 2 oxygen mixtures mixtures compound

Classifying Matter: Pure substance mixture Is the composition uniform? Can it be separated by physical means? Pure substance mixture Can it be decomposed by ordinary chemical means? Is the composition uniform? Homogeneous mixtures (air, sugar water, stainless steel) Heterogeneous mixtures (granite, blood) Compounds (ex: Water, NaCl, sucrose) Elements (ex: gold, aluminum,oxygen)

Symbols and Formulas Currently there are 117 elements Elements have 1 or 2 letter symbols, and compounds have formulas An elements first letter is always capitalized, if there is a second letter it is written lower case C – Carbon Ca – calcium K – potassium Au- gold

Symbols and Formulas In formulas, subscripts are used to indicate relative proportions of the elements in the compound Example H2O C12H22O11 This means that for every 2 Hydrogen atoms there is 1 Oxygen atom (Water) This means that for every 12 Carbon atoms there are 22 Hydrogen atoms and 11 Oxygen atoms (starch)

Periodic Table of the Elements Symbols and Formulas Periodic Table of the Elements

Section 2.4 Chemical Reactions Objectives Describe what happens during a chemical change Identify four possible clues that a chemical change has taken place Apply the law of conservation of mass to chemical reactions

Chemical Changes Chemical property The ability of a substance to undergo a specific chemical change is called a chemical property Iron plus oxygen forms rust, so the ability to rust is a chemical property of iron During a chemical change the composition of matter always changes Remember – in a physical change – substances present before the change are the same substances present after the change although they are no longer physically blended

Chemical Changes Chemical changes are also called chemical reactions During chemical reactions one or more substances are changed into new substances Reactants – Products – The products will have new properties different form the reactants you started with Materials you start with Materials you end up with

Recognizing Chemical Changes There are 4 clues that can serve as a guide to identify chemical changes Energy – is absorbed or released (temperature change indicates transfer of energy) Color change Gas production (bubbles, fizzing, odor change, smoke) Formation of a precipitate Precipitate – a solid that forms and separates from solution (will not dissolve) Only way to be sure that a chemical change has occurred is to test the composition of the sample before and after the change

Conservation of Mass During any chemical reaction… The mass of the products is always equal to the mass of the reactants All of the mass can always be accounted for Law of Conservation of Mass In any physical or chemical change, mass is conserved. Mass is neither created nor destroyed.