Chemical bonds

• 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 electronsValence Electrons the electrons in the outermost energy level of an atom -This Lithium Atom has one valence electron+ -+ +- 3. Counting Valence Electrons ---+ -+ ++--+-++ + + + + + +-+ ---+ -+ +-+---CarbonOxygenBeryllium4 valence electrons6 valence electrons2 valence electrons 4. How Many Valence Electrons? Hydrogen Lead Xenon Sulfur Sodium1 Valence Electron 4 Valence Electrons 8 Valence Electrons 6 Valence Electrons1 Valence Electron 5. The Octet Rule Atoms will combine to form compounds inorder to reach eight electrons in their outer energy level. Atoms with less than 4 electrons tend to loseelectrons. 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---5Notice 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 ---2Notice 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 levelelectrons (valence) of an atom The symbol for the element surrounded by as many dots as there are electrons in its outer energy level (valence) ExamplesAl :Aluminum..N : ..NitrogenMg :MagnesiumHow many valence electrons do each of these atoms have? 8. Making an Electron Dot Diagram Element X has 8 valence electrons Write down the elements symbol and place the first two dots on any side of the symbol.. XX: 1If 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 : 3Place 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 Electron6 Valence ElectronsHO How many valence electrons does each atom have?Ne 8 Valence ElectronsSr 2 Valence Electrons 10. Oxidation Number The charge that an atom would have if it lostor 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 :Magnesium2+Mg 11. What Could the Oxidation Number Be?H +1 or -1 because it can gain or lose one electronNe 0 because it will not gain or lose electronsO -2 because it will gain two electronsSr +2 because it will lose two electrons 12. 3 Types of Chemical Bonds Ionic CovalentMetallic 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 ideCl 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 ofelectrons Each pair of shared electrons creates a bond Usually occurs between atoms of non-metalsH O H --+-++ + + + + + +--+ -Example Water (H2O) 15. Types of Covalent Bonds Different covalent bond types share a differentnumber of electrons Water (H2O) -Carbon Dioxide (CO2)Nitrogen (N2)----+++ + + + + +++++ + + + + +- - -++ + + + +- - -++ + + + + + ++++ ++ + + --------------- - -++ + + + + + ------ --+Single Bonds Share 2 ElectronsDouble Bonds Share 4 ElectronsTriple 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 metalsAl3+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 givesrise to negative and positive regions of electric charge Results from an atoms electronegativity the ability to attract electrons to itself++Bonded hydrogen atoms showing equal sharing of electronsElectron Cloud++ + + + + + ++Hydrogen and fluorine bond with an unequal sharing of electronsWhy 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 bondsType: Diatomic - molecules consisting of two atoms of the same element bonded together Examples: H2, F2, O2, N2Compound A pure substance composed of two or more different elements (atoms) that are chemically combined Examples: CO, NO2, NaClWhat would you call something that has characteristics of both? 19. Molecule, Compound, or Both? 20. Chemical Reaction The process by which a chemicalchange 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? H2O2 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 LabExamples tearing paper cutting your hair change in statePhysical changes are not indicative of a chemical reaction 22. Chemical Change a change in which a substance becomes anothersubstance 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 usedand 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 Formulas2H2 + O2Chemical Formula2H2O SubscriptCoefficientCoefficient(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 ReactionEndothermic Reaction A chemical reaction in which A chemical reaction in whichenergy is released. The products have greater bond energy than the reactantsenergy is absorbed. The products have lower bond energies than the reactantsC6H12O6 + 6O2 6CO2 + 6H2O + energy (respiration)6CO2 + 6H2O + energy C6H12O6 + 6O2 (photosynthesis)Chemistry Comes Alive! Sample Movies TeacherTube - Videos Chemistry Demonstration VideosCan 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 contactwith 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 concentrationof methane molecules Catalysts (enzymes) organic substances that help speed upchemical 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 nordestroyed 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 ReactantsH 24 O 22ProductsHow 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 whichelements 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