Chemical Bonds & Reactions

Transcription

1 Chemical Bonds & Reactions

2 Chemical Bonding Do you understand how it works? What do you think when I pull out a bag of candy? I want that candy cause I don t have any! Does everyone think the same thing? Why? Nope, they don t! Because we aren t the same! What if you already had your own bag of your favorite candy? I don t need that candy cause I already got my own! What do you use to get the candy? My hands! Does candy change the way you feel during class? I want to participate so I can get some candy! Candy Bonding You want the candy when you don t have enough or any. You use your hands to get it. And it changes your mood and interest in the class.

3 Chemical Bonding I want that candy cause I don t have enough! We don t all want candy because we aren t the same! I don t need that candy cause I already got my own! Atoms are attracted to each other because they don t all have as many electrons as they want Not all atoms are attracted to other atoms because they have a different number of electrons Some atoms have exactly as many electrons as they want I use my hands to get that candy! Your hands are like the outer orbital with the valence electrons. I want to participate so I can get some candy! When atoms bond to change they number of electrons it affects their chemical and physical properties Chemical Bond An attractive force involving valence electrons that affects the chemical and physical properties

4 Valence Electrons This Lithium Atom has one valence electron Valence Electrons the electrons in the outermost energy level of an atom

5 Counting Valence Electrons Carbon 4 valence electrons Oxygen 6 valence electrons Beryllium 2 valence electrons

6 Let s Identify the Parts of this Atom! Proton () 6 Neutrons (no charge) 6 Electrons () 6 Period 2 = 2 Orbital Levels Group 14 = 4 Valence Electrons Carbon Atom

7 Determining the Number of Valence Electrons by Using the Periodic Table *Atoms of elements in Groups 1 and 2 have the same number of valence electrons as their group number. *Atoms of elements in Group 312 do not have a general rule relating their valence electrons to their group number. However, they typically have between 1 or 2 valence electrons. *Atoms of elements in Groups 1318 have 10 fewer valence electrons than their group number. (Exception helium atoms have only 2 valence electrons, even though they are in group 18)

8 1 # of Valence Electrons 2 Typically Typically 1 2

9 How Many Valence Electrons? Hydrogen Lead Xenon Sulfur Rubidium 4 Valence Electrons 6 Valence Electrons 1 Valence Electron 8 Valence Electrons 1 Valence Electron

10 The Octet Rule Octet Rule Atoms combine to form compounds in order to reach eight electrons in their outer energy level. I m pretty lazy Atoms with less than 4 electrons tend to lose electrons.. Yup, me, too! Atoms with more than 4 electrons tend to gain electrons. CONSIDER EIGHT A HAPPY NUMBER FOR ATOMS! Be aware that there are some exceptions!

11 The Octet Rule In Action 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. 2 1 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. 1 Where do you think Chlorine finds that one electron that it needs?

12 Chemical Bonding in Action! Chlorine Atom Sodium Chloride Sodium Atom You know, kind of like sharing candy!

13 3 Types of Chemical Bonds Ionic? Covalent? Metallic?

14 IONIC BONDS The force of attraction between oppositely charged ions. Occurs after a loss or gain of electrons (one atom is stronger than the other) Usually form between atoms of metals and atoms of nonmetals Compound names usually ends in ide Example Sodium Chloride (NaCl) Cl Na 1 1

15 Ionic Covalent Metallic oppositely charged ions attract loss or gain of electrons (one atom is stronger than other) usually between metals & nonmetals Metal Nonmetal Sodium Chloride NaCl Names usually end in ide

16 COVALENT BOND A force where atoms attract to complete octet (8 valence electrons) Atoms share electrons to create a bond (atoms have equal strength) Usually occurs between atoms of nonmetals H O H Example Water (H 2 O)

17 Ionic Covalent Metallic oppositely charged ions attract loss or gain of electrons (one atom is stronger than other) usually between metals & nonmetals atoms attract to complete octet (8 valence electrons) share electrons (Atoms have equal strength) usually between nonmetals Metal Nonmetal Hydrogen (1) Hydrogen (1) Oxygen (6) Sodium Chloride NaCl Names usually end in ide Dihydrogen Monoxide H 2 O

18 Metallic Bond A force where positively charged metal ions attract to 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 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Al 3 Notice how the electrons do not just stay with one ion

19 Ionic Covalent Metallic oppositely charged ions attract loss or gain of electrons (one atom is stronger than other) usually between metals & nonmetals atoms attract to complete octet (8 valence electrons) share electrons (Atoms have equal strength) usually between nonmetals Metal Nonmetal Hydrogen (1) Hydrogen (1) positive metal ions attract to electrons metal ions are held together by electrons usually between metals Valence electrons move around Sodium Chloride NaCl Names usually end in ide Oxygen (6) Dihydrogen Monoxide H 2 O positive ions are held together by electrons Copper, Silver, Gold Cu, Ag, Au

20 3 Types of Chemical Bonds Ionic? Covalent? Metallic?

21 Results of Bonding Molecule vs Compound Molecule 2 or more elements chemically combined Examples: O 2, H 2 O, CaCl 2, HCl, CH 4, P 4, CaSO 4 Diatomic molecule 2 or more of the same element chemically combined Examples: H 2, F 2, O 2, N 2, P 4 Compound 2 or more different elements chemically combined Examples: H 2 O, CaCl 2, HCl, CH 4, CaSO 4

22 Molecule or Compound?

23 Physical Change Change in shape, size, color, or state New substance is not formed Chemical composition does not change Change is reversible Physical changes are not indicative of a chemical reaction Physical Change A reversible change in shape, size, color or state but not chemical composition Examples tearing paper still paper cutting your hair still hair liquid water to ice still water

24 Chemical Change New substance is formed with new properties Nonreversible using ordinary physical means Changes that usually produce energy (heat, sound, light) or result in odor or fizzing/foaming Chemical Change a difficult to reverse change that creates a new substance and can produce energy, odor, or fizzing/foaming Examples mixing vinegar & baking soda creates carbon dioxide burning a piece of wood creates calcium carbonate soured milk creates lactic acid A chemical analysis is the only 100% way to know a chemical change has occurred.

25 Chemical Reaction A chemical change occurs Atoms rearrange: chemical bonds are broken and reform One or more substances change to produce one or more new substances Out of the four types of reactions, which would describe the chemical reaction taking place to the right? Chemical Reaction A chemical change where bonds break and atoms rearrange to produce a new substance Types 1. Synthesis (creating) 2. Decomposition (separating) 3. Combustion (burning) 4. Displacement/Replacement (switching) H 2 O 2

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28 Chemical Equation Short way to write the reactants that combine to form a product in a chemical reaction Reactants are the molecules at the start The product is the new molecules created when the reactants rearranged Can include if energy is produced or absorbed Chemical Equation a way to write how molecules rearrange in a chemical reaction and can include if energy is produced or absorbed

29 Components of a Chemical Equation Chemical Formulas Chemical Formula 2Na Cl 2 2NaCl Energy Coefficient Subscript (Reactants) (Yield) Coefficient (Products) Sometimes you will see a yields sign that looks like this. What do you think it means?

30 Chemical Equation Examples: 2H 2 O 2 CH 4 2O 2 C 6 H 12 O 6 6O 2 2H 2 O CO 2 2H 2 O 6CO 2 6H 2 O energy

31 Energy and Chemical Reactions Exothermic Reaction A chemical reaction in which energy is released. The products have greater bond energy than the reactants Endothermic Reaction A chemical reaction in which energy is absorbed. The products have lower bond energies than the reactants C 6 H 12 O 6 6O 2 6CO 2 6H 2 O energy (respiration) 6CO 2 6H 2 O energy C 6 H 12 O 6 6O 2 (photosynthesis)

32 Rates of Chemical Reactions The rate a chemical reaction takes place is based on the interaction (collisions) between the particles. Affect Chemical Reaction Rate: 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. Opening a valve to increase the amount of gas Catalysts (enzymes) organic substances that help speed up chemical reactions, but are not consumed in the reaction Ex. Stomach producing pepsin to aid digestion

33 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? H 2 O 2 H 2 O How would you balance this equation to show the conservation of mass?

34 Balancing Equation 1. Count the atoms of each element 2. Record the # of atoms under the correct side of the equation 3. Find the elements that do not have an equal number of atoms 4. Use a coefficient to add atoms so the numbers are equal 5. Remember to update the number of atoms for each element every time a coefficient is added 2 H 2 O 2 2 H 2 O Reactants H 42 O 2 Products H 24 O 12 How would you balance this equation to show the conservation of mass?

35 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:. N:. Mg: Aluminum. Nitrogen Magnesium How many valence electrons do each of these atoms have?

36 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 Sr 8 Valence Electrons 2 Valence Electrons

37 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: Mg: 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. Magnesium Mg 2

38 What Could the Oxidation Number Be? H O 1 or 1 because it can gain or lose one electron 2 because it will gain two electrons Ne Sr 0 because it will not gain or lose electrons 2 because it will lose two electrons

39 Types of Covalent Bonds Different covalent bond types share a different number of electrons Single Bonds Share 2 Electrons Double Bonds Share 4 Electrons Triple Bonds Share 6 Electrons Water (H 2 O) Carbon Dioxide (CO 2 ) Nitrogen (N 2 )

40 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 Electron Cloud Bonded hydrogen atoms showing equal sharing of electrons 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?