Chemistry review


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Review for 8th Grade Chemistry unit

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Chemistry review

  1. 1. Chemistry Review Chemical Building Blocks
  2. 2. As we review … think about these questions• How are matter and energy similar and how are they different?• How is the Periodic Table of the Elements used to help us understand matter?• How do physical and chemical changes affect matter?• How do we create models of something we can’t see?• Why do we create models in science?
  3. 3. Acid• Any of a class of compounds that form hydrogen ions when dissolved in water• Any of a class of compounds whose aqueous solutions react with bases and certain metals to form salts.• Acids turn blue litmus paper red• Acids have a pH of less than 7.• Acids taste sour• Acids conduct electricity in solution
  4. 4. Atom• the smallest particle an ELEMENT can be divided into … and still be the same substance
  5. 5. AtomConsists of a Nucleus (Protons (+) & Neutrons)surrounded by Electrons (-)
  6. 6. Atomic Mass• the average mass of the most common form (isotope) of an element• sometimes also called the Atomic Weight
  7. 7. Base• Any of a class of compounds that form hydroxyl ions (OH) when dissolved in water• Any of a class of compounds whose aqueous (water-based) solutions react with acids to form salts.• Bases turn red litmus paper blue• Bases have a pH greater than 7.• Their aqueous solutions have a bitter taste.• Bases feel slippery• Bases dissolve fats and oils
  8. 8. Boiling point & Melting point• BOTH are characteristic properties of matter which mark a transition from one state (phase) of matter to another • Boiling point – the temperature in Celsius at which a substance will boil. Marks the transition from liquid state to gaseous state, AKA condensation point (gas  liquid)• Melting point – the temperature in degrees Celsius at which a substance will melt. Marks the transition from solid state to liquid state, AKA freezing point (liquid  solid)
  9. 9. Chemical• A chemical is any substance created by chemistry.
  10. 10. Chemical [change]• A chemical change produces a new substance• Change takes place on a molecular level• Cannot be reversed
  11. 11. Compound• a substance made of two of more different elements that are CHEMICALLY combined• Compounds are not changed by physical changes … only chemical changes• A compound has different chemical properties to the elements that formed it Elements• The elements are present in FIXED ratios, never random combinations Compounds
  12. 12. Density• Mass per unit volume. Density = Mass ÷ Volume• A measure of how close together the molecules in a particular substance are packed• Density determines whether or not something will float• If density > water, it will sink• If density < water, it will float
  13. 13. Endothermic/ Exothermic• Endothermic – a process or chemical reaction that is accompanied by the absorption of heat• Endothermic reactions take in energy from the surroundings • Exothermic – a process or chemical reaction characterized by or causing the liberation or release of heat • Exothermic reactions transfer energy to the surroundings
  14. 14. Gas• matter that can change shape and volume (can expand or compress)• Note: the concept of density applies to gases also
  15. 15. Ion• An atom or compound that carries an electric charge
  16. 16. Liquid• matter that has a definite volume, but takes the shape of the container holding it.
  17. 17. Mass• the amount of matter in an object; a measure of the inertia of an object 1,000 cm3 of water = 1,000 mL = 1 Liter
  18. 18. Matter• any substance which has mass and occupies space.
  19. 19. Metal• Any of a large group of chemical elements, including iron, gold, copper, lead, and magnesium, that readily become cations (+ ion) and form ionic bonds, having relatively free valence electrons (electrons in the outer shells)• Metals are good conductors of electricity.• Metals conduct heat well, and in solid form are relatively malleable and ductile (can be pressed/molded into different shapes) when compared to other solids.• They are usually shiny and opaque.• All metals, except mercury, are solid at room temperature.
  20. 20. Everything in blue is a metal
  21. 21. Mixture• consists of two or more substances that are NOT chemically bonded• There are two kinds of mixtures • Heterogeneous – the parts of the mixture are not distributed evenly • Homogeneous – the parts of the mixture are evenly distributed• A solution is a very well-mixed homogeneous mixture. E.g. saltwater
  22. 22. Molecule• the smallest unit a substance can be divided into and still have the chemical properties and composition of the substance. Examples: Oxygen (O2) and water (H2O)
  23. 23. Neutral• Neither acid nor alkaline (pH = 7).• Having no inherent or net charge (like a neutron)
  24. 24. Non-metal• an element that doesn’t have the characteristics of metal including: ability to conduct heat or electricity, luster, or flexibility. Everything in YELLOW is a non-metal.
  25. 25. Oxidation• the process when oxygen combines with another element, changing the appearance of the element.• Oxidation is an example of a chemical change
  26. 26. Physical [change]• A physical change is a type of change in which the form or phase of matter is altered but one substance is not transformed into another. Can be reversed.
  27. 27. Radioactive• Description of an element that gives off energy waves called radiation• Radioactivity is the emission of radiation by unstable atomic nuclei undergoing radioactive decay
  28. 28. Reactivity• the tendency of a substance to undergo chemical reaction, either by itself or with other materials, and to release energy. Sodium reacting with water
  29. 29. Solid• matter that has a definite shape and volume
  30. 30. Solubility• the ability of a substance to dissolve• Solubility is one of the characteristic properties of matter• A saturated solution cannot dissolve any more of the solute
  31. 31. Solution• A mixture in which particles of one or more substances (the solute) are distributed uniformly throughout another substance (the solvent), so that the mixture is homogeneous at the molecular or ionic level• A saturated solution cannot dissolve any more of the solute
  32. 32. Volume• The amount of space occupied by a three- dimensional object or region of space. Volumes are expressed in cubic units.
  33. 33. Weight• the force that gravity exerts upon a body• Warning: Chemists sometimes use the word weight when they REALLY mean mass!
  34. 34. States (Phases) of Matter
  35. 35. Characteristic Properties of Matter• Characteristic properties of matter do not change• A characteristic property (either a chemical or a physical property) is so unique to a particular substance that it is used to identify the substance. Examples: • Density • Melting/boiling point • Solubility
  36. 36. Elements, Compounds, and Mixtures
  37. 37. Remember those questions …• How are matter and energy similar and how are they different?• Matter is the stuff that everything is made of.• Energy is a property of matter. Energy is what makes matter do stuff.
  38. 38. The same amount of matter can have differentamounts of energy and so represent different statesof matter. For example, if you add energy to an icecube made of water, it becomes liquid water, and ifyou add even more energy, it becomes steam. Thekind of matter and the amount of matter is the sameas in the original cube, but there is more energy.
  39. 39. Remember those questions …• How is the Periodic Table of the Elements used to help us understand matter? The main purpose of any periodic table of the elements is to help us understand the relationships among the various elements. • Elements in the same group have similar reactive properties • Elements in the same period gain a proton and an electron from left to right.
  40. 40. Remember those questions …• How do physical and chemical changes affect matter? Physical changes change the form or phase (state) of matter, but not its chemical composition. Example: melting ice changes water from its solid phase to its liquid phase. Chemical changes change the composition of matter; changing the matter into a new substance with new chemical properties. Example: combining the elements sodium (Na) and chlorine (Cl) forms NaCl, which is table salt.
  41. 41. Remember those questions …• How do we create models of something we can’t see? We use a combination of observation and inference. We experiment and do our best to model what we can observe. Then we refine our model to fit our latest understandings.
  42. 42. Remember those questions …• Why do we create models in science? Models are used when it is either impossible or impractical to create experimental conditions in which scientists can directly measure outcomes. A scientific model is a way to represent observations, phenomena, and physical processes in a logical and objective way. Examples: Using trail mix to model a mixture in chemistry. Drawing a picture of an atom.
  43. 43. Now you know that …• Everything in the universe is composed of matter and energy.• All kinds of matter can be identified based on their physical and chemical properties.• An atom is the basic unit of every element.• All the matter in the universe is characterized in the Periodic Table of the Elements• Interactions between atoms cause chemical changes that produce new substances with different chemical properties.