Introduction to Chemistry Matter and Change Chapters 1 & 2

What is Chemistry? The study of matter, its properties and the changes it underdoes What is Matter? Anything that has mass and takes up space

What is Mass? The amount of matter an object contains What is Volume? The amount of space occupied by matter

Why Study Chemistry? Helps us better understand nature Helps us understand how things work (cleaning products, pharmaceuticals, shampoos, biology) Can improve quality of life (plastics, permanent press, recycling processes, medical treatments) Develops critical thinking skills, analytical skills, skills to organize and manage information

Fields of Chemistry Organic Analytical Physical Inorganic Polymer Medicinal Environmental Biochemistry

How We Study Chemistry Collect data (observations, measurements) Analyze data (tables, graphs, calculations) Interpret & Explain data Draw conclusions Evaluate data Design new experiments Understand and evaluate what others have done Develop models and theories Identify laws

Scientific Method Questions/Observations Hypothesis Design Experiment Collect Data Analyze Data Revise Hypothesis

Theories and Laws Theory Well-tested explanation for a broad set of observations Law A statement that summarizes observations but does not explain them

What is a Model? A representation May or may not be to scale May represent something very large or something very small Models take many forms… a diagram, a graph, a physical model Used to help explain a concept

Characteristics of States of Matter Property Solid Liquid Gas Mass   Shape Volume Compressible? Effect of Temp on Expansion

Characteristics of States of Matter Property Solid Liquid Gas Mass Definite Shape Indefinite Volume Compressible? No Yes Effect of Temp on Expansion Slight Moderate Large

Molecular Representation of States of Matter

How we describe matter Substance A sample of matter having a constant (uniform or definite) composition. It can be either an element or a compound.

How we describe matter Element A substance that cannot be decomposed into simpler substances by chemical or physical means. It consists of atoms having the same atomic number.

How we describe matter Compound A substance with constant composition that can be broken down into elements by chemical processes.

How we describe matter Allotrope Different forms of the same element Example: Carbon: diamond, graphite, buckyballs Phosphorus: red, white, black

Allotropes of Phosphorus White phosphorus can be transformed to red, black or violet by in creasing temperature or pressure By Weißer_Phosphor.JPG: BXXXD at de.wikipedia Phosphor_rot.jpg: Tomihahndorf Phosphor-rot-violett.jpg: Maksim derivative work: Materialscientist [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons https://commons.wikimedia.org/wiki/File%3APhosphComby.jpg

How we describe matter - Particles Atom Smallest particle of an element that retains the properties of that element; the fundamental unit of which elements are composed

How we describe matter - Particles Molecule A bonded collection of two or more atoms of the same element or different elements. A representative particle of a molecular compound. Examples: Br2, CH4, H2O

Properties of Matter Extensive property Depends upon the amount of matter in a sample Examples – mass, volume Intensive property Depends upon the type of matter, not the amount Example – density, absorbancy

Properties of Matter Physical Property A quality or condition of a substance that can be observed or measured without changing the substance’s composition

Examples of Physical Properties Density State Boiling Point Solubility Melting Point Ductility Color Malleability Odor Conductivity Luster Hardness

Properties of Matter Chemical Property Ability to form new substances

Examples of Chemical Properties Reactivity – reacts, neutralizes Flammability – burns Note: The fact that a substance does NOT react is a chemical property

Physical or Chemical Property? Water melts at 0oC Propane burns in air Leaves turn color in the fall Lead is a very dense metal

Physical and Chemical Changes Physical Change A change in the physical form of a substance but not its chemical composition; Chemical bonds are not broken

Physical and Chemical Changes The change of one substance into another substance through a reorganization of the atoms by breaking or making of chemical bonds; A chemical reaction

Indicators of Chemical Change Unexpected color change Formation of a precipitate Evolution of a gas Change in energy

Differentiating Between Physical or Chemical Change Physical change does not alter the composition of a substance though it may alter the appearance of the substance Key words Bend Boil Break Melt Crush Solidify Dissolve Evaporate

Differentiating Between Physical or Chemical Change Examples Salt dissolves in water. Solubility is a physical property so the change is physical. A liquid boils and is converted from a liquid to a gas. Boiling point is a physical property. A change in state is a physical change.

Molecular Description of Change in State

Differentiating Between Physical or Chemical Change Chemical change produces a different substance; composition and properties are different. Requires a chemical reaction to reclaim the starting material. Not always easily done! Reactants  Products

Differentiating Between Physical or Chemical Change Key words that indicate a chemical change: Reacts Precipitates Burn s Explodes Bubbles Emits Fizzes A flame Gives off

Differentiating Between Physical or Chemical Change Examples A match lights when struck Substances are combined and light is emitted An antacid tablet fizzes when added to water

How to differentiate between physical and chemical change Physical change does not alter the composition of a substance although it may alter its appearance Chemical change produces a different substance

Mixture A combination of two or more substances that are not chemically combined. The components of the mixture is variable (can be made up differently at different times).

Types of Mixtures Homogeneous Mixture: Completely uniform in composition Components are not distinguishable A solution

Homogeneous Mixtures Examples: Salt water Stainless steel Sugar in water Gasoline Brass Clean air Jello

Composition of Common Alloys – Solid Solutions 14 K Gold 39 % Gold 25% Silver 39% Copper Sterling Silver 93% Silver 7% Copper Coinage Silver 90% Silver 10 % Copper Pewter 85% Tin 6% Bismuth 5% Antimony Cast Iron 96% Iron 4% Carbon

Types of Mixtures Heterogeneous Mixture: Not uniform in composition Components are readily distinguishable Different composition in different parts of the mixture

Heterogeneous Mixtures Examples: Tossed salad Soil Granite

Mixture lingo Phase Any part of a system with uniform composition and properties. Homogeneous mixtures consist of one phase Heterogeneous mixtures consist of two or more phases (e.g., vinegar and oil)

Classification of Matter Differentiate whether a sample is a substance (element or compound) or a mixture (homogeneous or heterogeneous)

Separation of Mixtures Mixtures of substances can be separated by physical means. The mixtures may be homogeneous or heterogeneous. One or more processes may be required to separate mixtures. Make use of type of mixture and physical properties of its components to select the best means of separation.

Techniques for Separation of Mixtures Filtration Evaporation Extraction Chromatography Distillation Decantation Sieve Magnet Centrifuge Forceps

Examples Water and salt Water and ethanol Salt and sand Sand and wood chips

How are physical & chemical properties used? Identification Reactivity Separation of mixtures State of substance under certain conditions

Physical Properties of Some Common Substances Formula State Color Melting Point (oC) Boiling Point Density (g/cm3) Neon Ne Gas Colorless -249 -246 0.0009 Oxygen O2 -218 -183 0.0014 Ethanol C2H5OH Liquid -117 78 0.789 Chlorine Cl2 Greenish-yellow -101 -34 0.0032 Mercury Hg Silvery white -39 357 13.5 Bromine Br2 Red-brown -7 59 3.12 Water H2O 100 13.00 Sulfur S Solid Yellow 113 445 2.07 Sucrose C12H22O11 White 185 d* 1.59 Sodium chloride NaCl 801 1413 2.17 d, decomposes on heating.

Changes in State

Given physical properties and current temperature, what is the state of the substance? BP SOLID LIQUID GAS Increasing Temperature

If temperature is 45 oC, what is state of water? (liquid) Water: mp = 0 oC, bp = 100 oC   If temperature is 45 oC, what is state of water? (liquid) If temperature is -29 oC, what is state of water? (solid) If temperature is 150 oC, what is state of water? (gas)

Bromine: mp = -7 oC, bp = 59 oC   If temperature is -59 oC, what is state of bromine? (solid) If temperature is 28 oC, what is state of bromine? (liquid) If temperature is 83 oC, what is state of water? (gas)

Symbols and Formulas Element or chemical symbols Al = Aluminum C = Carbon Pb = Lead Many symbols based on Latin or German names