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Unit 2 Matter and Energy
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Chemistry is… …the study of the composition, structure, and properties of matter and the changes it undergoes Matter Anything that has mass and occupies space (volume)
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Classification of Matter
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An Element A pure substance made of only one kind of atom. Cannot be simplified. EXAMPLE: Hydrogen An Atom The smallest unit of an element that maintains the properties of that element.
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Element Song! Tom Lehrer: http://youtu.be/DYW50F42ss8 Harry Potter:
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Compound A substance that is made from the atoms of two or more elements that are chemically bonded. EXAMPLES: NaCl or H2SO4 Molecule A neutral group of two or more atoms that are held together by covalent bonds EXAMPLES: O2 or H2O All compounds are molecules but not all molecules are compounds! EXAMPLE: O2 is a molecule but not a compound because it is composed of a single element.
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Are you ready for this? An imperfect analogy…
Imagine going to an ice cream store. Let's say that they have 30 different flavors of ice cream. Those are elements, the things that I have available to build my dessert from. The smallest amount of ice cream that the store will sell to me is a scoop. This is an atom. If I want, I can put two or more scoops of ice cream together. This is a molecule. If my molecule has more than one flavor of ice cream, I can call it a compound.
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Reading Compounds Subscripts: Coefficients:
The little number to the right of the element in the compound Tell you the number of atoms in each compound Coefficients: The large number before the compound Tells you how many molecules of the compounds you have
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Practice Try these below…. Remember 1 Na2CO3 1 6 2 Al2O3 3 KCl
a new element is indicated with a new capital letter If there is no number written, 1 is assumed # of Molecules # of Atoms Per Compound # of Atoms Total 1 Na2CO3 1 6 2 Al2O3 3 KCl
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Laws About Compounds Law of Definite Composition
A pure compound has the same ratio of atoms always Ex. Water is always H2O Law of Multiple Proportions Elements can combine in different ratios to give different compounds Ex. Hydrogen Peroxide H2O2
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Mixtures Two or more substances/matter which are mixed but are not combined chemically. Each retains its own properties. -Despite that there are no chemical changes to its components, the physical properties of a mixture may differ from those of the components. Such as melting point. EXAMPLE: adding salt to water changes the boiling point and melting point Therefore, why do we add salt to roads in the winter?
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EXAMPLES OF MIXTURES HETEROGENOUS -not uniform in composition EXAMPLE: Salad dressing HOMOGENOUS -uniform in composition EXAMPLE: Water
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Heterogeneous vs. Homogeneous
Milk HOMOGENEOUS
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Heterogeneous vs. Homogeneous
Blueberry Muffin HETEROGENEOUS
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Heterogeneous vs. Homogeneous
Water HOMOGENEOUS
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Heterogeneous vs. Homogeneous
Ice Water HETEROGENEOUS
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Heterogeneous vs. Homogeneous
Orange Juice (with pulp) HETEROGENEOUS
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Heterogeneous vs. Homogeneous
Orange Juice (without pulp) HOMOGENEOUS
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Heterogeneous vs. Homogeneous
Air HOMOGENEOUS
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Heterogeneous vs. Homogeneous
Water and Oil HETEROGENEOUS
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Heterogeneous vs. Homogeneous
Trail Mix HETEROGENEOUS
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Heterogeneous vs. Homogeneous
Soda (aka Coke) HETEROGENEOUS
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Types of Mixtures: Solutions
- A homogenous mixture consisting of two or more substances in a single phase. -The solute dissolves in the solvent EXAMPLE: sugar dissolved into water
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Types of Mixtures: Suspension
-mixture of two or more ingredients, where the particles are typically large enough to be seen Solid-Solid Solid-Liquid Liquid-Liquid
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Types of Mixtures: Colloid
-A substance microscopically dispersed throughout another substance. Can be a solid, liquid, or gas. Example: milk jell-o
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Separation of a Mixture
The constituents of the mixture retain their identity and may be separated by physical means (distillation, chromatography, filtration, vaporization).
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Separating Mixtures Filtration - porous barrier separates solid from liquid Distillation - liquids separated by differences in boiling point Crystallization - forms pure solids from dissolved substances Chromatography - separation based on ability to travel or be drawn across a material
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filtration
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distillation
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crystallization
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chromatography
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Properties of Matter Physical Properties: A characteristic that can be observed or measured without changing the identity of the substance Chemical Properties: The ability of a substance to undergo change that transforms it into a different substance Nuclear Properties: Characteristics that involve changes in nuclear identity (atomic number or atomic mass number) or in the arrangement of nuclear energy levels of the substance being tested.
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Which is which? Physical or Chemical property?
melting point solubility boiling point reactivity freezing point density ability to oxidize color odor flammability combustibility malleability toxicity
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Physical Properties of Matter Can be Extensive or Intensive
Extensive properties depend on the amount of matter that is present. Intensive properties does not depend on the amount of matter present.
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Which is which? Extensive or Intensive property?
Volume Boiling point Energy content Density Melting point Mass Ductility Length Elasticity Extensive Intensive
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Changes of Matter Physical Changes : A change in a substance that does not involve a change in the identity of the substance. Hint: if you can change it back-it is typically a physical change EXAMPLES: crushing, cutting, melting, boiling, freezing, breaking, sublimating, dissolving… Chemical Changes : A change in which one or more substances are converted into different substances. (Chemical reaction) *Hint: Heat and light are often evidence of a chemical change! EXAMPLES: rusting, combusting, metabolizing, cooking, digesting, baking… C2H5OH O2 2 CO2 + 3 H2O + Energy Reactants Products
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Which is which? Physical or Chemical change?
Water boiling Ice melting Cutting your hair An acid neutralizing a base Breaking a piece of glass Cooking an egg Your bike rusting Sublimating dry ice Casting silver in a mold Wood burning Digesting food Bending melt to form a bridge Metabolizing sugar Mixing red and blue marbles Milk sours Water freezing Dissolving sugar into water
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Three Phases SOLID LIQUID GAS
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Phase Differences Solid – definite volume and shape; particles packed in fixed positions. Liquid – definite volume but indefinite shape; particles close together but not in fixed positions Gas – neither definite volume nor definite shape; particles are at great distances from one another Plasma – high temperature, ionized phase of matter as found on the sun.
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Copper Phases - Solid
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Copper Phases - Liquid
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Copper Phases – Vapor (gas)
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PHASE CHANGE Involves PHYSICAL CHANGES from solid to liquid, liquid to solid, liquid to gas, etc Particles absorb or release heat during phase changes NOTE: THE TEMPERATURE OF THE MATTER DOES NOT CHANGE DURING A PHASE CHANGE!
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HEAT AND MATTER KINETIC ENERGY – energy of motion
kinetic energy changes with temperature changes POTENTIAL ENERGY – energy of position potential energy changes during phase changes
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Common Phase Changes endothermic exothermic condensation deposition
sublimation vaporization Fusion/melting Freezing/crystallization endothermic exothermic
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endothermic exothermic h Temp & Kinetic energy changing
Potential energy constant Potential energy changing Temp & Kinetic energy constant endothermic exothermic h
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HEAT ENERGY Energy is absorbed or released as heat in chemical or physical changes – energy involved can be measured DURING PHYSICAL/CHEMICAL CHANGES ENERGY AND MATTER ARE CONSERVED! Law of Conservation of Energy- Energy is not created or destroyed-only changes forms Heat energy impacts particle motion (atoms, ions, molecules) – more heat, more motion; less heat, less motion
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Kinetic–Molecular Theory of Matter
Developed in late 19th century to account for behavior of atoms and molecules Based on idea that particles of matter are always in motion, and have more energy as the temperature increases: KINETIC ENERGY = ENERGY OF MOTION Used to explain properties of solids, liquids & gases in terms of the energy of particles and forces that act between them
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