4 What are "pure substances"? Matter that has a fixed composition and definite properties. (chemical and physical)
5 There are two kinds of pure substances ElementsCompounds
6 ElementsSubstance that cannot be separated or broken down into simpler substances by chemical means.Ex’s- any box on the periodic tableMade of only 1 type of atomThe smallest unit of an element thatmaintains the properties of that elementHUH?
7 The smallest unit of an element that maintains the properties of that element??? The element sodium has certain properties11 protons, 11 electrons…boiling point, etc
8 Compounds cont…Substance made of atoms of 2 or more different elements that are CHEMICALLY combined.Elements are combined in a definite way and this changes their propertiesNa- lethal if ingested Cl- lethal if ingestedNaCl- table salt
9 Molecules Two or more atoms bonded together… Ex- O2, NaCl, etc. Not all molecules are compounds, but all compounds are molecules…explain
10 What is a pure substance? CompoundsMolecules made by two or more elements bonded together -always in a definite ratioElementsMolecules made of just one elementThe two categories of pure chemical substances.Na (sodium)NaCl (sodium chloride/salt)
11 Characteristics of Pure Substances Cannot be separated into simpler substances by physical methods (physical changes)Fixed compositionProperties do not varyCan be expressed with a chemical formulaEx H2O, NaCl, HBasic characteristics of pure substance:
15 Characteristics of Mixtures Components retain their characteristic properties and can be separated by physical means.Basic identification of a mixture.This sand and iron filings mixture can be separated using a magnet.
17 Homogenous Mixtures Homogenous mixtures look the same throughout Types: solutions, alloys, etc.Example: salt water, brass
18 Indicators of Homogenous Mixtures Have the same composition throughoutComponents are indistinguishableWill not scatter lightParticle size is smallBrainstorm more examples of homogenous mixtures.
19 Can they still be separated by physical means ? YES!!! It may be more complicated, but it can be done…distillation , centrifugation
20 Homogeneous mixtures are called solutionsSolutions are …homogenous mixtures that do not scatter light.separated by physical means (including distillation or evaporation.)created when something is completely dissolved in pure water.Examples: sugar water, salt water
21 Parts of a Solution Solute- substance that dissolves in solvent ex. Salt (“U dissolve”)Solvent- substance that does the dissolving (ex.water)Well, not really, because you don’t dissolve, but you get the picture
22 Why don’t you dissolve? You are not “Miscible” Miscible- two or more liquids that can dissolve into each otherImmiscible- liquids that do NOT mixEx- oil and water
23 Heterogenous Mixtures Heterogeneous mixtures are composed of large pieces that are easily separated by physical means (ie. density, polarity, metallic properties).
24 Indicators of Heterogenous Mixtures Do not have same composition throughoutComponents are distinguishableParticle size is medium or largeExamples: fruit salad, vegetable soup, etc.Brainstorm more examples of heterogenous mixtures.
25 Tyndall EffectScattering of light due to particles
26 Heterogenous Mixtures Types ofHeterogenous Mixtures1. Colloid –medium particlesParticles stay suspended in the mixture and scatter light (Tyndall effect)Ex- mayonnaise, milk, fog
27 Heterogenous Mixtures Types ofHeterogenous Mixtures1. Suspension- large particlesTyndall effectParticles will settle out when the mixture is allowed to standEx-muddy water, OJ with pulp
28 What kind of changes does matter undergo? PhysicalChemical
29 physical propertiesPhysical properties are those that we can determine without changing the identity of the substance we are studying.Properties we can observe or measureEx- color, state of matter, etc
30 Physical Properties of Matter PropertyDescriptionExampleHardnessAbility of 1 substance to scratch anotherDiamond can scratch glassViscosityResistance to flowingWater= low visc.Honey= high visc.SolubilityAbility to dissolve in waterNaCl dissolves easily in water so it’s soluble
31 Physical Properties of Matter PropertyDescriptionExampleSuperconductorSubstance that conducts electricity at lower temperaturesTin, aluminum, used in trainsSemiconductorSubstance that has a resistance b/w a conductor & insulatorSilicon-used in computers or radios
32 DENSITYMass per unit volumeCalculated by:Density= Mass/VolumeD=M/V
34 Examples of physical properties: Hardness, color, melting point and density are all physical properties.The physical properties of sodium (NaCl) metalsoft, lustroussilver-colored metalrelatively low melting pointlow density.
35 What is a physical change? A physical change occurs when the substance changes physically but does not change its chemical composition.For example: water freezing into ice, cutting a piece of wood into smaller pieces, etc.The form or appearance has changed, but the properties of that substance are the same (i.e. it has the same melting point, boiling point, chemical composition, etc.)Definition of physical changes.
36 Physical Changes Temperature Color Conducting electricity Dissolving MeltingBoilingFreezingColorConducting electricityDissolvingPhysical changes are characterized by the following:
37 What are chemical properties? Chemical properties describe the way a substance can change or react to form other substances.These properties, then, must be determined using a process that changes the identity of the substance of interest.
38 How can chemical properties be identified? One of the chemical properties of alkali metals such as sodium and potassium is that they react with water. To determine this, we would have to combine an alkali metal with water and observe what happens.In other words, we have to define chemical properties of a substance by the chemical changes it undergoes.
39 What are chemical changes? A chemical change occurs when a substance changes into something new.This occurs due to heating, chemical reaction, etc.You can tell a chemical change has occurred if the density, melting point or freezing point of the original substance changes. Many common signs of a chemical change can be seen (bubbles forming, mass changed, etc).Definition of chemical change.
40 Characteristics of Chemical Changes Baking soda reacting w/ vinegarYou can’t go back to the original substances after a chemical change (reaction) has occurred!!Chemical Changes are characterized by the following:Burning wood
42 Conservation of Matter LawofConservation of MatterThere is no observable change in the quantity of matter during a chemical reaction or a physical change.In other words, matter cannot be created nor destroyed. It is just converted from one form to anotherDefinition of Conservation of matter.