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Chemistry Notes

Chemistry Notes. Molecules. A molecule consists of two or more atoms of the same element, or different elements, that are chemically bonded together. The smallest part of a pure substance (element or compound) Ex. One molecule H 2 0 vs. a glass of water. Molecules.

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Chemistry Notes

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  1. Chemistry Notes

  2. Molecules • A molecule consists of two or more atoms of the same element, or different elements, that are chemically bonded together. • The smallest part of a pure substance (element or compound) • Ex. One molecule H20 vs. a glass of water.

  3. Molecules • Diatomic molecule - composed of two of the same atom • Examples: H2, N2, O2, Cl2, Br2 • In the animation above, two nitrogen atoms • (N + N = N2) make one Nitrogen molecule .

  4. Compounds • Two or more different types of atoms chemically bonded to each other • Table Salt & Ammonia • are examples of compounds • Compounds have different properties than the elements it is made of. • All compounds are molecules, but not all molecules are compounds (diatomic molecules are NOT compounds)

  5. Compounds cont… • Organic Compounds-compounds containing covalently bonded carbon. • Example: C6H12O6 (Glucose)

  6. Octet Rule • The rule of 8. • Valence electrons are the electrons in the outermost energy level. • You must know the number of valence electrons an atom has. • When atoms chemically combine they try to end up with a full outermost energy level or 8 valence electrons by either gaining or losing electrons. • To meet this need: • Metals tend to lose (give away) electrons. • Nonmetals tend to gain electrons.

  7. Octet Rule • Nature seeks balance! Having a full outermost energy level is stable. • That’s why the Noble Gases do not react. They already have a full outer level.

  8. Groups & Periods • The group (column) represents the number of valence electrons in the outer shell. • The period (row) represents the number of energy levels in the atom.

  9. Lewis Dot Structure • A Lewis dot diagram is a system to represent atoms and their valence electrons.

  10. Lewis Dot Structure • Drawing Lewis Dot Structures:

  11. Ionic Bonds • An ionic bond is a bond that forms when valence electrons are lost or gained (transferred). It is the bond formed between oppositely charged ions. Example: • A lithium atom gives up an electron to a fluorine atom. • The result is a positively charged lithium ion and a • negatively charged fluoride ion.

  12. Ionic Bonds • Other ionic bond examples…….

  13. Ionic Compounds • A metal bonded to a nonmetal • (Groups 1 & 2 with Groups 6 & 7) • Conducts electricity when dissolved in water or melted. • High melting points. • Solids at room temperature.

  14. Metallic Bonds A metallic bond is the attraction of free floating valence electrons. • Metal atoms can bond to atoms of the same element, or to other metals. • Electrons divide evenly • among atoms- “electron sea”

  15. Metallic Compounds A metallic compound is a metal bonded to another metal. • Metallic compounds have: • High melting points • Good conductors of heat and electricity • Malleable and ductile • Strong bonds • Atoms arranged in a pattern

  16. Covalent Bonds • A covalent bond is a chemical bond formed when atoms share valence electrons. Usually nonmetals with nonmetals. • Elements that are close together on the periodic table are more likely to share electrons in a covalent bond than to transfer electrons. • Hydrogen, Carbon, Nitrogen, and Oxygen usually form covalent bonds.

  17. Covalent Bonds • Drawing covalent bonds…..

  18. Single Covalent Bonds • Hydrogen has one unpaired electron. • Two hydrogen atoms share their single • electrons to form a pair. • The shared pair of electrons • is a single covalent bond, • which holds the hydrogen • molecule H2 together.

  19. Single Covalent Bonds Drawing single covalent bonds….

  20. Double & Triple Bonds • Some atoms may form stronger bonds by sharing more than one pair of electrons. • A double bond has two pairs of shared electrons and is stronger than a single bond. • A triple bond has three pairs of shared electrons and is stronger than a double bond.

  21. Double & Triple Bonds Drawing double & triple bonds….

  22. Covalent Bonds • Drawing covalent bonds…..

  23. Rule of HONC-1234 Hydrogen, Oxygen, Nitrogen, and Carbon make up 98% of all living things

  24. Rule of HONC-1234 • Every Hydrogen atom has 1 line connecting it to other atoms. • Every Oxygen atom has 2 lines connecting it to other atoms. • Every Nitrogen atom has 3 lines connecting it to other atoms. • Every Carbon atom has 4 lines • connecting it to other atoms.

  25. Covalent Compounds • Do not conduct electricity in water. • More flammable than ionic compounds. • Softer than ionic compounds. • Low melting and boiling points. • Usually do not dissolve in water (not soluble)

  26. Chemical/ Molecular Formulas • Information about the atoms that make up a molecule/compound • Atoms will combine in specific rations due to the number of electrons shared or transferred. Example: • The chemical formula for sucrose, C12H22O11, • includes all the atoms in one molecule.

  27. Using Oxidation numbers to Write Molecular Formula • Step 1: Determine the elements to be used in the formula and their oxidation numbers Mg +2 F -1 • Step 2 Solve by making the charge of one atom the subscript for the other. Mg +2 F -1 = Mg F2 **If the subscript is 1, you do not need to write it.

  28. Using Oxidation numbers to Write Molecular Formula • Try it: • Sodium Chloride • Calcium Fluoride • Carbon Tetrachloride • Aluminum Oxide • Magnesium Oxide • Carbon Dioxide **If the subscript is 1, you do not need to write it.

  29. Polymers • A polymer is a covalent compound made up of many repeating units linked together in a chain. • Analogy = Beaded Necklace • A monomer is a single molecule that forms a • link (beads) in a polymer chain (necklace).

  30. Polymers • Examples of Polymers: • Carbohydrates • Plastics • Proteins • DNA • Rubber

  31. Acids and Bases • Acids are substances that release a positively charged hydrogen ion, H+, in water. The strength of the acid depends on the concentration of H+ ions. • Acids are also used in making many products, such as • fertilizers, detergent, and cleaners. • Acids are important in several body processes, including breaking down food in the stomach. Acid Properties • Can neutralize a base • Turn blue litmus paper red • pH between 1-6 • Sour • Feel like water • Conduct electricity • React with metals

  32. Acids and Bases • Bases are substances that produce negatively charged hydroxide ions (OH-) when dissolved in water. • Common bases include baking soda and cleaning agents. Base Properties • Feel slippery • Bitter taste • Turn red litmus paper blue • Dissolve fats, oils, and grease • Neutralize acids to produce salt and water • Conduct electricity • Have a pH between 8-14 Acids and Bases

  33. The pH Scale • pH is a numerical scale used to determine the strength or weakness of an acid or base. • The pH scale runs from 0 to 14 • Acids are below 7; strong acids are near 0. • Bases are above 7; strong bases near 14. • Neutral solutions have a pH of 7.

  34. The pH Scale • pH can be measured using different indicators: • Litmus paper (red or blue) • pH paper (pool test strips) • Universal indicator (cabbage juice) • pH meter

  35. The pH Scale

  36. Mixtures • A mixture is a combination of two or more substances that can be separated by physical means (i.e. filtering, evaporation, magnet, etc.) • NO CHEMICAL BOND • Solutions are also mixtures. Solutions • Solutions are groups of molecules that are mixed up in a completely even distribution.

  37. Mixtures Homogeneous Mixture • Also called solution • Uniform appearance • Evenly mixed at the atomic level • Ex: blood, milk, metal alloy, air

  38. Mixtures Homogeneous Mixture Heterogeneous Mixture • Also called solution • Uniform appearance • Evenly mixed at the atomic level • Ex: blood, milk, metal alloy, air • Not evenly mixed • Distinct substances • Ex: granite, mixed nuts, salad, salad dressing

  39. Physical vs. Chemical Property Physical properties can be observed without changing the substance. Ex: phase of matter, color, taste, odor, shape, texture, density, melting point, boiling point, hardness, conductivity, malleability

  40. Physical vs. Chemical Property

  41. Physical vs. Chemical Property A chemical property is the ability or inability of a substance to combine with or change into one or more new substances (how a substance reacts with other substances). • Examples of chemical properties include burning or rusting. • Some • substances • do not react.

  42. Physical vs. Chemical Property

  43. Physical vs. Chemical Change • Physical change: What the substance is made of does not change. Physical changes are reversible. • Ex) Changing from one state to another • Other Examples: • Cutting a lawn, breaking glass, • Melting ice

  44. Physical vs. Chemical Change • Chemical change: Change one substance into a new substance. • Chemical bonds are formed/rearranged • New substances have different properties and compositions than the original substances. • Usually chemical changes cannot be easily reversed. Property Changes

  45. Chemical Reactions • If a substance reacts with another substance, it means there is an attraction between atoms. A Chemical Bond formed! Not easily separated. • Evidence that a chemical change (reaction) has occurred • Heat produced/absorbed • Gas produced (bubbles/fizzing) • Odor produced • Electricity produced • Light produced • Precipitate produced (solid/solute coming out of solution) • Color change (weakest evidence!)

  46. Chemical Equations • Chemical equations show that in chemical reactions, atoms rearrange, but no atoms are gained or lost.

  47. Writing a Chemical Equation • Reactants are the original substances in a chemical reaction • and are placed on the left side. • Products are the new substances in a chemical reaction and • are placed on the right side. reactant + reactant product original substances new substance/s

  48. Counting Atoms • A subscript tells how many atoms • of an element are in • one molecule. • A coefficient tells how many • atoms, molecules, or formula units • are in a reaction.

  49. Writing a Chemical Equation NaHCO3 + CH3COOH CO2 + H2O + NaC2H3O2

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