Presentation on theme: "Physical and Chemical Changes Pure Substances Mixtures States of Matter."— Presentation transcript:
Physical and Chemical Changes Pure Substances Mixtures States of Matter
What is matter? Matter is anything that takes up space and has mass.
What is matter? The building blocks of matter are atoms and compounds. An atom is the smallest unit of an element that still has all the properties of the element An element is a pure substance that has only one type of atoms
What is matter? A compound is made of two or more types of atoms that are chemically bonded A molecule is the smallest unit of an element or compound that retains all the properties of that element or compound
Matter is identified based on its properties
Properties ColorShapeTextureDensity Melting and boiling point Electrical conductivity Heat conductivity MalleabilityDuctilityReactivity Index of Refraction FlammabilityHardness Vapor pressure
Properties can be divided into two types; Physical & Chemical
Chemical properties can not be observed and measured without changing the identity of the matter. Chemical properties are harder to observe than physical properties.
Chemical properties Reaction with acids Reaction with bases (alkalis) Reaction with oxygen (combustion) Ability to act as oxidizing agent Ability to act as reducing agent Reaction with other elements Decomposition into simpler substances Corrosion
Physical properties Can be observed and measured without changing the identity of the matter Color, density, malleability
Properties Can be intensive or extensive
Intensive properties Are Independent (does not depend on) of the amount of matter ColorOdor Luster - How shiny a substance is. Malleability - The ability of a substance to be beaten into thin sheets. Ductility - The ability of a substance to be drawn into thin wires. Conductivity - The ability of a substance to allow the flow of energy or electricity. Hardness - How easily a substance can be scratched. Melting/Freezing Point - The temperature at which the solid and liquid phases of a substance are in equilibrium at atmospheric pressure. Boiling Point - The temperature at which the vapor pressure of a liquid is equal to the pressure on the liquid (generally atmospheric pressure). Density
Extensive properties does change with the amount of matter Mass - A measurement of the amount of matter in a object (grams). Weight - A measurement of the gravitational force of attraction of the earth acting on an object. Volume - A measurement of the amount of space a substance occupies. Length
physical change A physical change occurs when a substance does not change into something new The properties of a substance do not change Ice melting is still water Physical changes are easy to undo
Matter can undergo changes A chemical change occurs when a substance changes into something new. This occurs due to heating, chemical reaction, etc.
Matter can undergo changes You can tell a chemical change has occurred if the properties, like density, of the original substance changes Chemical changes are usually not reversible
Signs of a chemical change chemical Formation of a gas Formation of a solid (precipitate) Color change (Unexpected) Release of light or heat
Matter Matter can be either A pure substance or a mixture of substances
What is a pure substance? A pure substance has only one type of matter in the sample
Cannot be separated into simpler substances by physical methods (physical changes like sieving or centrifuging) Can only be changed in identity and properties by chemical methods Properties do not vary Characteristic of Pure Substances
What is a Pure Substance? Compounds Can be decomposed into simpler substances by chemical changes, always in a definite ratio Elements Cannot be decomposed into simpler substances by chemical changes
What is a Pure Substance? Compounds Consists of two or more different types of atoms (molecules) (molecules) H 2 O Elements Consist of only one kind of atom, Can exist as either atoms (e.g. argon) or molecules* (e.g., nitrogen).
Molecules *Molecules consist of two or more atoms of the same element, or different elements, which are chemically bound together. Note that the two nitrogen atoms that make up a nitrogen molecule move as a unit. N 2
Atoms Elements are made up of atoms, Atoms are the smallest particle that has the properties of the element.
Pure Substances Compound –composed of 2 or more elements in a fixed ratio –properties differ from those of individual elements –EX: table salt (NaCl) Sodium is a solid shiny metal which reacts w Courtesy Christy Johannesson
Pure Substances Law of Definite Composition –A given compound always contains the same, fixed ratio of elements. Law of Multiple Proportions –Elements can combine in different ratios to form different compounds. Courtesy Christy Johannesson
Pure Substances For example… Two different compounds, each has a definite composition. Carbon, C Oxygen, O Carbon monoxide, CO Carbon, C Oxygen, O Oxygen, O Carbon dioxide, CO 2 Courtesy Christy Johannesson
Mixtures Variable combination of 2 or more pure substances. Variable combination of 2 or more pure substances. HeterogeneousHomogeneous Courtesy Christy Johannesson
Mixtures Is a collection of pure substances simply mixed together. The composition is variable – can change The properties of each pure substance remains intact. Mixtures are two or more substances that are NOT chemically combined. Mixtures do not have constant properties
Mixtures Mixtures are two or more substances that are NOT chemically combined.
Homogeneous Mixtures Homogeneous mixtures look the same throughout but can be separated by physical means (centrifuge, filtering, picking out pieces, density, boiling, magnetism etc.). Examples: milk, salt water, sand and sugar
Have the same composition throughout Components are indistinguishable May or may not scatter light Examples: soda, air Signs of a Homogeneous Mixture
Solutions Solutions are homogenous mixtures that do not scatter light. These mixtures are created when something is completely dissolved in pure water. They are easily separated by distillation or evaporation. Examples: sugar water, salt water
Suspension - a type of mixture Suspension –heterogeneous –large particles –Tyndall effect –particles settle –EX:fresh-squeezed lemonade Courtesy Christy Johannesson
Heterogeneous Mixture Heterogeneous mixtures are composed of large pieces that are easily separated by physical means (ie. density, polarity, metallic properties).
Do not have same composition throughout Components are distinguishable – easy to tell that it is different Examples: fruit salad, granite Signs of a Heterogeneous Mixture
Mixtures Examples of mixtures are milk,wood,concrete,air,granite, motor oil, chocolate, and elephants.
MATTER Can it be physically separated? Homogeneous Mixture (solution) Heterogeneous MixtureCompoundElement MIXTUREPURE SUBSTANCE yesno Can it be chemically decomposed? noyes Is the composition uniform? noyes Courtesy Christy Johannesson
Classification of Matter Materials Homogeneous Heterogeneous mixture Homogeneous mixture Substance ElementCompoundSolutionMixture Specific / General Order / Disorder Smoot, Smith, Price, Chemistry A Modern Course, 1990, page 43
Elements, Compounds, and Mixtures (a) an element (hydrogen) (b) a compound (water) (c) a mixture (hydrogen and oxygen) (d) a mixture (hydrogen and oxygen) Dorin, Demmin, Gabel, Chemistry The Study of Matter, 3 rd Edition, 1990, page 68 hydrogen atoms hydrogen atoms oxygen atoms
Methods of Separation: FiltrationSieving Gravity separation Distillation and Condensation Crystallization and Evaporation Flotation Magnetic separation ChromatographyCentrifuging
Distillation Commercial Tequila still Copper alcohol still
Solids Liquids Gases
Gas, Liquid, and Solid Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 441 Gas Liquid Solid
Have a definite shape Have a definite volume Molecules are held close together and there is very little movement between them. Kinetic Molecular Theory
Solid H 2 O (s) Ice Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31
Have an indefinite shape Have a definite volume Kinetic Molecular Theory: Atoms and molecules have more space between them than a solid does, but less than a gas (ie. It is more fluid.)
Liquid H 2 O (l) Water Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31 In a liquid molecules are in constant motion there are appreciable intermolecular forces molecules are close together Liquids are almost incompressible Liquids do not fill the container
Have an indefinite shape Have an indefinite volume Kinetic Molecular Theory: Molecules are moving in random patterns with varying amounts of distance between the particles.
Gas H 2 O (g) Steam Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31
Some Properties of Solids, Liquids, and Gases Property Solid Liquid Gas Shape Has definite shapeTakes the shape of Takes the shape the container of its container Volume Has a definite volumeHas a definite volume Fills the volume of the container Arrangement of Fixed, very closeRandom, close Random, far apart Particles Interactions between Very strongStrong Essentially none particles
Changing states requires energy in either the form of heat. Changing states may also be due to the change in pressure in a system.
Changing of States Freezing – Liquid Solid – exothermic Melting – Solid liquid – endothermic Evaporation– Liquid gas –endothermic Condensation- Gas liquid -exothermic Sublimation Solid gas endothermic Deposition Gas solid -exothermic