1. Unit 2: All Biology is Chemistry Lesson 2: Compounds and Chemical Bonding

2. Objectives At the conclusion of this lesson students will be able to: 1.Define compound.compound 2.Explain why elements combine to form compounds. 3.Define the term chemical bond.chemical bond 4.Compare and contrast ionic and covalent bonds.ioniccovalent bonds 5.Understand why ionic and covalent bonds form. 6.Predict which type of bond will likely form when given two or more elements.

3. Compounds Most elements do not exist alone in nature. Atoms combine to form compounds. –Compounds are substances containing atoms of two or more elements that are chemically combined in fixed proportionsCompounds Obj. 1 & 2 Obj. 1 & 2Compound: from the Latin componere, meaning “to put together”

4. Why Combine? Compounds form because most atoms are not stable in their natural state. A partially-filled outermost energy level is not as stable as an energy level that is completely filled with the maximum number of electrons it can hold. Is this carbon atom stable? = neutron = proton = electron Obj. 1 & 2 Obj. 1 & 2

5. Two Ways to Bond Ionic Bonds Covalent Bonds

6. Modeling Ionic Bonds Activity In your notes, draw a Bohr model of a sodium atom (atomic number 11). Next to the sodium atom draw a Bohr model of a chlorine atom (atomic number 17). Use the directions in your packet to correctly draw the atoms and assign their electrons to energy levels.

7. Achieving Stability Atoms become stable by attaining at least one of the following: –They fill their outermost, or valence, energy level with the maximum amount of electrons that it will hold.valence OR –They fill their outermost energy level with eight electrons. The ‘Rule of Eight’

8. The Sodium-Chlorine Ionic Bond Sodium 11 p 12 n Chlorine 17 p 18 n Sodium atom (atomic #: 11)Chlorine atom (atomic #: 17) How many electrons does each atom have now? How does this affect the total charge of each atom?

9. The Sodium-Chlorine Ionic Bond Sodium 11 p 12 n Chlorine 17 p 18 n These atoms are no longer electrically neutral. Protons+11 Electrons-10 Charge+1 Protons+17 Electrons-18 Charge-1 These atoms are stable, but because of their opposite charges they now attract one another. How many protons does sodium (Na) have? How many electrons does Na have now? What is the total charge of this atom of sodium?

10. The Sodium-Chlorine Ionic Bond An atom with an electrical charge is called an ion. chlorine ions As a result of their opposite charges, sodium ions and chlorine ions attract each other. Sodium 11 p 12 n Chlorine 17 p 18 n Sodium ion +1 Chlorine ion An ionic bond is the chemical bond formed between ions with opposite charges.ionic bond Obj. 4 & 5 Obj. 4 & 5 This new substance is a compound called sodium chloride.

11. Predicting the Tendency of Atoms to Ionic Bond © Art Branch, Inc.

12. Ionic Bonds Reviewed Ionic bonds… involve a __________ of electrons. result when ______ of ___________ charges attract each other. Back to Two Ways to Bond

13. Drill 15 October 2009 Students should answer the following questions in their notebooks: a.A _________ ________ is an attraction that holds two or more atoms together to form a compound. b. Atoms can become more stable by filling their outermost energy level with ______ electrons. c.An atom with an electrical charge is called an ____________. d.A(n) _______ ________ is the chemical bond formed between ions with opposite charges.

14. There IS Another Way What happens when an atom has 4, 5, or even 6 valence electrons? Atoms can also share one or more pairs of electrons. –When two atoms share electrons, the shared electrons occupy orbitals around both of the atoms. –The electrons move so quickly that it is difficult to predict which atom they are orbiting at any given time.

15. Water – A Model of Covalent Bonding Hydrogen 1 p 0 n Oxygen 8p 8n Hydrogen atom (atomic #: 1)Oxygen atom (atomic #: 8) How many valence electrons does each atom have? How many more electrons does each atom need to fill its outermost energy level? Obj. 5 Obj. 5

16. Water – A Model of Covalent Bonding Hydrogen 1 p 0 n Oxygen 8p 8n Hydrogen 1 p 0 n This is a molecule of water. It can also be referred to by its chemical formula, H 2 O. A shared pair of electrons can be considered to be part of the outermost energy level of both atoms that share them. This is a molecule of water. It can also be referred to by its chemical formula, H 2 O. A shared pair of electrons can be considered to be part of the outermost energy level of both atoms that share them. How might each of these atoms fill its outermost energy level? Hydrogen 1 p 0 n Oxygen 8p 8n If each hydrogen atom shares a pair of blinking electrons with oxygen, how many valence electrons does each atom have?

17. Covalent Bond Covalent Bond A covalent bond forms when two atoms share one or more pairs of electrons.covalent bond –A molecule is the simplest part of a substance that retains all the properties of that substancemolecule Obj. 2 Obj. 2

18. Organic Compounds Carbon has an outermost energy level that is partially filled. Its outermost level contains only four electrons. Because of this carbon can form many covalent bonds with other atoms and create a wide variety of compounds. This is why carbon is an essential element for all life. = neutron = proton = electron Compounds that contain one or more atoms of carbon are called organic compounds.organic compounds

19. How Do Atoms Transfer or Share Electrons? The Atomic Mosh Pit Your favorite band is playing at a local under- 18 club. You decide to attend the concert. At the club, concert-goers begin to slam-dance as the band begins their set. How will concert-goers change their dancing if the band changes the speed of the music? What are some things that could occur when concert- goers begin dancing quickly?

20. Back to the Dance Floor Just like the concert- goers, atoms also have energy of motion or kinetic energy.kinetic energy –Normally negatively- charged electrons of different atoms repel each other. –If the kinetic energy is large enough, it can overcome this repulsion and the electrons of the two atoms can interact and bond. Mosh Pit by Dan Witz

21. All That Energy! This kinetic energy can… –be lost as heat or light, or –be stored in a chemical bond. Chemical bondsChemical bonds are the attractions that hold two or more atoms together to form a compound. Bonds form  energy is stored Bonds broken  energy is released Obj. 3 Obj. 3

22. Comparing Ionic & Covalent Bonds Ionic bonds Covalent bonds Electrons are transferred Electrons are shared Usually occur when group IA and IIA elements bond with group VIIA elements. Usually occur between nonmetals (i.e. C, H, N, O) 2 nd strongest type of chemical bond Strongest type of chemical bond Examine the following table: Obj. 4 Obj. 4

23. Drill Complete the Venn Diagram. Ionic BondsCovalent Bonds Obj. 4 Obj. 4

24. Guess the Bond! Examine each set of elements below. Which sets will likely bond together using ionic bonds? Which ones will likely bond using covalent bonds? Na & Cl C & H Mg & Cl K & I N & O Si & O H & S Obj. 6 Obj. 6

25. Glossary – Part 1 chemical bond chemical bond – an attraction that holds two or more atoms together to form a compound covalent bond covalent bond – chemical bond in which two atoms share one or more pairs of electrons ionion – an atom or molecules that has an electrical charge ionic bond ionic bond – chemical bond formed from the attractive forces between ions of opposite charges

26. Glossary – Part 2 kinetic energy kinetic energy – energy of motion moleculemolecule – is the simplest part of a substance that retains all the properties of that substance organic compound organic compound – a compound that contains the element carbon valencevalence – refers to the outermost energy level of an atom or the electrons contained in that outermost energy level

27. Works Cited Campbell, Neil A., Brad Williamson, and Robin J. Heyden. Biology: Exploring Life. Upper Saddle River, NJ: Pearson Education, 2004. Coulbourn, Dixon. "Slammin'." 12 Oct 2006. Emsley, John. The Elements. 3rd. Oxford: Clarendon Press, 1998. Postlethwait, John H., and Janet L. Hopson. Modern Biology. Austin, TX: Holt, Rinehart and Winston, 2006. Witz, Dan. "Mosh Pit." 1998. DFN Gallery. 12 Oct 2006.