Chemical bonds
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  • 1. Chemical Bonding
  • 2. Chemical Bond  A force of attraction that holds two atoms together  Has a significant effect on chemical and physical properties of compounds  involves the valence electrons Valence Electrons – the electrons in the outermost energy level of an atom - This Lithium Atom has one valence electron + - + + -
  • 3. Counting Valence Electrons - - - + - + + + - - + - ++ + + + + + + - + - - - + - + + - + - - - Carbon Oxygen Beryllium 4 valence electrons 6 valence electrons 2 valence electrons
  • 4. How Many Valence Electrons?  Hydrogen  Lead  Xenon  Sulfur  Sodium 1 Valence Electron 4 Valence Electrons 8 Valence Electrons 6 Valence Electrons 1 Valence Electron
  • 5. The Octet Rule  Atoms will combine to form compounds in order to reach eight electrons in their outer energy level.  Atoms with less than 4 electrons tend to lose electrons.  Atoms with more than 4 electrons tend to gain electrons.  Be aware that there are some exceptions! CONSIDER EIGHT A HAPPY NUMBER FOR ATOMS!
  • 6. The Octet Rule In Action 6 - 7 - - - 5 Notice how this chlorine atom has seven valence electrons, one away from eight. It will try to gain one more according to the Octet Rule. - - - + + ++ + ++ + + + ++ + ++ ++ - 4 - - 1 - 3 - - - - - 1 - - - 2 Notice how the sodium atom has one valence electron. It is this electron that it will try to get rid of according to the Octet Rule. - + ++ + + + + + ++ + - - - - Where do you think Chlorine finds that one electron that it needs?
  • 7. Lewis Structure (Electron Dot Diagram)  a way of drawing the outer energy level electrons (valence) of an atom  The symbol for the element surrounded by as many dots as there are electrons in its outer energy level (valence)  Examples Al : Aluminum . .N : . . Nitrogen Mg : Magnesium How many valence electrons do each of these atoms have?
  • 8. Making an Electron Dot Diagram Element “X” has 8 valence electrons Write down the element’s symbol and place the first two dots on any side of the symbol. . X X: 1 If this were an atom of an element from group 1, you would just place the one dot on any side of the element. . .X : . 4 .. .X : . 5 . X: 2 . .X : 3 Place the rest of the dots in either a clockwise or counter clockwise manner around the symbol, with no side receiving two dots until each side gets one. .. :X: . 6 .. :. .: X 7
  • 9. What Would the Electron Dot Diagram Look Like? 1 Valence Electron 6 Valence Electrons H O How many valence electrons does each atom have? Ne 8 Valence Electrons Sr 2 Valence Electrons
  • 10. Oxidation Number  The charge that an atom would have if it lost or gained electrons; ionic charge  Can be helpful in determining which atoms will interact or bond with each other  Example: According to electron dot diagram for Magnesium, it has two valence electrons. Because Magnesium is “unhappy” with two, it will typically lose them. If this happens it will turn into a Magnesium ion. At this point it will have an oxidation number of +2. Mg : Magnesium 2+ Mg
  • 11. What Could the Oxidation Number Be? H +1 or -1 because it can gain or lose one electron Ne 0 because it will not gain or lose electrons O -2 because it will gain two electrons Sr +2 because it will lose two electrons
  • 12. 3 Types of Chemical Bonds Ionic Covalent Metallic What can you describe about each of these bonds just by looking at the name?
  • 13. IONIC BONDS  The force of attraction between oppositely charged ions.  Occurs after a transfer or loss/gain of electrons  Usually form between atoms of metals and atoms of non- metals  Resulting compounds have a name that usually ends in – ide Cl 1- - Na 1+ - - - - - - - - ++ + + + + + + - - - ++ + + + + + + - - - - - - - - - - Example - Sodium Chloride (NaCl) Which different groups or families of elements will mostlikely interact to create these types of bonds?
  • 14. COVALENT BOND  A force that bonds two atoms together by a sharing of electrons  Each pair of shared electrons creates a bond  Usually occurs between atoms of non-metals H O H - - + - ++ + + + + + + - - + - Example – Water (H2O)
  • 15. Types of Covalent Bonds  Different covalent bond types share a different number of electrons Water (H2O) - Carbon Dioxide (CO2) Nitrogen (N2) - - - - + ++ + + + + + + + ++ + + + + + - - - ++ + + + + - - - ++ + + + + + + + ++ + + + + - - - - - - - - - - - - - - - - - ++ + + + + + - - - - - - - - + Single Bonds Share 2 Electrons Double Bonds Share 4 Electrons Triple Bonds Share 6 Electrons
  • 16. Metallic Bond  A force of attraction between a positively charged metal ion and the electrons in a metal  Many metal ions pass along many electrons  Many properties of metals, such as conductivity, ductility, and malleability, result from the freely moving electrons in the metal  Usually occurs between atoms of metals Al3+ Al3+ - Al3+ Al3+ Al3+ Al3+ Al3+ Al3+ Al3+ Al3+ Al3+ Al3+ Al3+ Al3+ - Al3+ Al3+ Al3+ Al3+ Al3+ Al3+ - Al3+ Al - 3+ Al3+ - Al3+ Al3+ Al3+ Al3+ Al3+ Al3+ Al3+ - - - Al3+ Al3+ Al3+ - Al3+ - Al3+ Al3+ Al3+ - Al3+ Al3+ Al3+ Notice how the electrons do not just stay with one ion
  • 17. Unequal Sharing (Polar Covalent Bond)  The unequal sharing of electrons between two atoms that gives rise to negative and positive regions of electric charge  Results from an atom’s electronegativity – the ability to attract electrons to itself + + Bonded hydrogen atoms showing equal sharing of electrons Electron Cloud ++ + + + + + + + Hydrogen and fluorine bond with an unequal sharing of electrons Why do you think the two Hydrogen atoms share equally, but the Hydrogen and fluorine do not?
  • 18. Results of Bonding Molecule A neutral group of two or more non-metal atoms held together by covalent bonds Type: Diatomic - molecules consisting of two atoms of the same element bonded together Examples: H2, F2, O2, N2 Compound A pure substance composed of two or more different elements (atoms) that are chemically combined Examples: CO, NO2, NaCl What would you call something that has characteristics of both?
  • 19. Molecule, Compound, or Both?
  • 20. Chemical Reaction  The process by which a chemical change occurs  Atoms are rearranged, and chemical bonds are broken and reformed  One or more substances change to produce one or more different substances  Types     What does H2 & O2 gas create? Synthesis (creating) Decomposition (separating) Combustion (burning) Displacement/Replacement (switching) Out of the four types of reactions, which would describe the chemical reaction taking place to the right? H2 O2
  • 21. Physical Change  a change in shape, size, color, or state  a change without a change in chemical composition  a change that is reversible  The Mixtures Lab Examples tearing paper cutting your hair change in state Physical changes are not indicative of a chemical reaction
  • 22. Chemical Change  a change in which a substance becomes another substance having different properties  a change that is not reversible using ordinary physical means  Changes that usually cause, heat, sound, light, odor, fizzing/foaming, color changes You usually need more than one of the above characteristics to be considered a chemical change! Examples mixing vinegar & baking soda burning a piece of wood soured milk A chemical analysis is the only 100% way to know a chemical change has occurred.
  • 23. Chemical Equation  Shorthand form for writing what reactants are used and what products are formed in a chemical reaction  Sometimes shows whether energy is produced or absorbed  Examples: 2H2 + O2  2H2O CH4 + 2O2  CO2 + 2H2O C6H12O6 + 6O2  6CO2 + 6H2O + energy
  • 24. Components of a Chemical Equation Chemical Formulas 2H2 + O2 Chemical Formula  2H2O Subscript Coefficient Coefficient (Yield) (Reactants) (Products) Sometimes you will see a “yields” sign that looks like this. What do you think it means?      Subscripts
  • 25. Energy and Chemical Reactions Exothermic Reaction Endothermic Reaction  A chemical reaction in which  A chemical reaction in which energy is released.  The products have greater bond energy than the reactants energy is absorbed.  The products have lower bond energies than the reactants C6H12O6 + 6O2  6CO2 + 6H2O + energy (respiration) 6CO2 + 6H2O + energy  C6H12O6 + 6O2 (photosynthesis) Chemistry Comes Alive! Sample Movies TeacherTube - Videos Chemistry Demonstration Videos Can you think of other reactions where energy is gained or released?
  • 26. Rates of Chemical Reactions The rates at which chemical reactions can take place are based on the interaction (collisions) between the different particles. These rates can be impacted by the following:  Temperature –a measure of the average kinetic energy of the particles in a sample of matter  Ex. Increasing the temperature when cooking  Surface area – amount of material that comes into contact with the reactants  Ex. Cutting a potato into smaller pieces when cooking  Concentration – amount of substance per volume  Ex. Turning the valve on a gas stove to increase the concentration of methane molecules  Catalysts (enzymes) – organic substances that help speed up chemical reactions, but are not consumed in the reaction
  • 27. Law of Conservation of Mass  Proposed by Antoine Lavoisier  In a chemical reaction, atoms are neither created nor destroyed  All atoms present in the reactants are also present in the products  Chemical equations must account for/show the conservation of mass  balancing equations In its present form, does this chemical equation show a conservation of mass? 2 H2 + O2  2 H2O Reactants H  24 O  22 Products How would you balance this equation to show the conservation of mass? H  24 O  12
  • 28. Hints For Balancing Equations  Count the atoms  List the number of atoms of each element to see which elements must be balanced  Use a coefficient to add atoms to one side of the equation  Start with the reactant or product that has the greatest number of different elements  Add a coefficient to another reactant or product  Make sure that the coefficients in your balanced equation are the smallest whole numbers possible (they should have no common factor other than one) Tutorial on Balancing Equations