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Unit 14: Chemical Bonding

Unit 14: Chemical Bonding. Have your periodic table handy. Chemical Bonding. Bond noun 1. Something that binds Read this passage about bonding:

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Unit 14: Chemical Bonding

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  1. Unit 14: Chemical Bonding Have your periodic table handy

  2. Chemical Bonding Bond noun 1. Something that binds Read this passage about bonding: Imagine you are walking down the street with your best friend. A market has a bin of apples for sale. A sign says that the apples cost forty cents each. You both want an apple, but your friend has only 35 cents while you have 45 cents. What can you do? It doesn’t take you long to figure out that if you give your friend a nickel, you can each buy an apple. Transferring the nickel to your friend gets both of you what you want. Your actions model, in a simple way, what can happen between atoms.

  3. Before we continue lets review… there are two types of “changes” matter can undergo 1) Physical Change 2) Chemical Change New matter is made Two elements join (or separate) into a “new” product Example: H2 + 0 → H20 How do we know: -Gas bubbles -Color change -Energy release (light and/or heat) -Unable to reverse • No “new” matter –it just looks different • Water to ice = H20→H20

  4. The passage about the apples/sharing is very representative to the behavior atoms display • Mostelements want to bond with other elements • Elements want to form bonds to become “happy” • Happiness means there is stability • To become happy/stable elements share or give electrons • This behavior is known as chemical bonding • Compounds/molecules are formed through these chemical reactions

  5. How many electrons are needed for happiness…? -The magic number is 8 -And it’s the valence electrons that are given/shared -8 valence electrons makes atoms/elements happy = the octet rule Remember, valence electrons are the furthest from the nucleus and can be determined very easily amongst the A-Series elements!

  6. Take a look… Sulfur Electron Shell Diagram · Sulfur has _____ valence electrons, it needs ____ to be happy *A series 6, Period 3 Argon Electron Shell Diagram · Argon has _____ valence electrons, it needs ____ to be happy *A series 8, Period 3 Sodium Electron Shell Diagram · Sodium has _____ valence electrons, it needs ____ to be happy *A series 1, Period 3 Remember most elements want to bond. The Noble gasses (Group 18, A-Series 8a) are naturally stable (happy) because they already have 8 valence electrons. This is why they do not form bonds.

  7. Classifying the Happiness To get happy atoms/elements either share or give (transfer) valence electrons 2 common types of sharing, or bonds • Ionic Bonds 2) Covalent Bonds Remember, these bonds are another way to say “chemical reaction” so compounds/molecules are formed!!!

  8. Ionic Bond DEFINITION -These bonds transfer electrons -Formed with attractions between two oppositely charged ions ***Ion is atom with a +/- charge Anion = negative ion Cation = positive ion -Once ions come together, their charges cancel each other out, therefore the compound becomes neutral. This bond creates a compound

  9. Ionic Bond EXAMPLE Reactions between metals and nonmetals form ionic compounds. These reactions occur easily between the metals of Group 1 (1a) and non-metals of Group 17 (7A). NaCl Reaction: Na Transfer to Cl 1a 7a 11 Na Sodium 22.990 17 Cl Chlorine 35.453 Na Na Cl Cl

  10. Ionic Bond PROPERTIES The characteristic properties of ionic compounds include: Crystal Shape –due to the alternating charges of the bond a pattern forms High Melting Points -it takes a lot of energy to overcome the attractive forces Electrical Conductivity –ions have electric charges (must break apart first)

  11. Covalent Bond DEFINITION • Bond formed by sharing electrons • Both atoms attract the shared electrons at the same time • There can be unequal sharing, causing the electrons to move closer to one atom • If electrons move closer, the compound can have a slight electrical charge • Polar covalent bond (has charge) • Non-polar covalent bond (no charge –equal sharing) • Covalently bonded elements generally form molecules

  12. Covalent Bonds EXAMPLE covalent bonds form between nonmetals Polar Covalent Bond Non-polar Covalent Bond chlorine: Cl2 When atoms are identical, the valence electrons are shared equally The key is that there is an even distribution of charge due to equal sharing of electrons Water: H20 Slightly positive Hydrogen molecules attract to slightly negative Oxygen The key is that there is uneven distribution of charge due to uneven sharing of electrons

  13. Covalent Bond PROPERTIES • Covalently bonded molecules have definite and predictable shapes (like water) • Covalent bonds are very strong too • They have low melting and boiling points (opposite of ionic bonds) • Covalent bonds can have more than one bond… -Single –shares one electron pair between two atoms -Double –shares two electron pairs between two atoms -Triple –shares three electron pairs between two atoms See the following slides for illustrations of these bonds, when we say “pairs” think of the electron dot diagrams (EDD)

  14. Different types of Covalent bonds • Single Covalent Bonds

  15. Different types of Covalent Bonds • Double Covalent Bonds

  16. Different types of Covalent Bonds • Triple Covalent Bonds Remember covalent bonds happen between at least two non-metal elements

  17. Summary of Differences Ionic Bonds -Transfer electrons -Oppositely charged ions -Balanced electrical charge (neutral) -Metal to nonmetal Example: NaCl -Crystal shapes, high melting points -Form compounds Covalent Bonds -Share electrons -Can have unbalanced electrical charge (polar) -Nonmetals to nonmetals Example: H20 -Definite & predictable shapes, low melting points, multiple bond types -Form molecules ***See “cheat sheets” to help memorize

  18. More Types of Bonds Polyatomic Bonds -A group of covalently bonded atoms -Multiple atoms -Usually has a charge because of the collection of atoms has gained or lost an extra electron Metallic Bonds -Occurs between metal elements -Has ions surrounded by a sea of electrons -Have the metal qualities: Strength, conductivity, malleable, ductile & luster

  19. Cheat Sheet 1: Big Picture Matter is either… element rare Noble Gases mixture compound stable Most common No new matter, no chemistry like compounds unstable Ionically Bonding Octet Rule Covalently Bonding Stable = 8 VE Unstable = seeking to satisfy octet rule ALWAYS changing! polyatomic metallic

  20. Cheat Sheet 2: Major/Minor Bonds Bonds Between Elements Ionic major minor Covalent Polyatomic Metallic

  21. Cheat Sheet 3: Ionic Bonds Ionic Bonds metals + non-metal High Melting Points Neutral Conductors Crystal Shape Transfer electrons NaCl Cation + Anion - strong Compounds

  22. Cheat Sheet 4: Covalent Bonds Covalent Bonds non-metal + non-metal H2O Molecules High Melting Points Share electrons 3 ways Shape Polar Non-polar predictable single double definite unequal = sharing triple strong

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