Compounds & Bonds – Unit 5

1. Compounds & Bonds – Unit 5 Why do atoms bond to form compounds? How are bonds formed? How do we represent compounds (names and formulas)?

2. Chemical Bonds • Review sources • http://bcs.whfreeman.com/thelifewire/content/chp02/02020.html • http://www.sciencegeek.net/Chemistry/taters/directory.shtml • http://ed.ted.com/lessons/the-science-of-macaroni-salad-what-s-in-a-mixture-josh-kurz

3. Bonding Essentials • Bonds are formed when valence electrons are gained, lost or shared by atoms • There are 3 major types of bonds • Ionic, Covalent, Metallic • Compounds are 2 or more atoms bonded together, with different properties than their elements.

4. Metals and Non-metals Act Differently

5. Atomic Theater • Demonstrating bonding • Ionic – 2 students • Covalent – 2 students • Metallic – 4 students

6. Chemical Bonds • http://ed.ted.com/lessons/how-atoms-bond-george-zaidan-and-charles-morton

7. Electronegativity • Ability of an atom in a compound to attract electrons from another atom. • Difference between electronegativity of atoms is used to determine the bond type.

9. Electronegativity Differences • Electronegativity Differences = ∆EN O 3.2

10. Determining bond type Determine the absolute difference (either + or -) Type? O ___ - N____= _____ O ___ - O____=_____ O ___ - H____=_____ F____- Li ____=_____

11. Periodic Table with Electronegativities Electronegativity Values for Elements Circle elements with highest & lowest value & label. Show trends for EN using arrows.

12. Electronegativity Learning Guide • Determine absolute differences • Classify each bonding pair of elements as: • Ionic • Covalent • If covalent, determine if the bond is: non-polar (∆ 0 – 0.3) or polar (∆0.4 – 1.7)

13. Types of Bonds Ionic Covalent Metallic

14. Ionic Bond • Ionic Bond: formed with Bonds a __________ with a ____________ Valence electrons are ________________ from the ___________ to the __________. Therefore, when the valence electron(s) are transferred to the ____-______, the NM become _______ charged (a ________).

15. Ionic Bond∆EN = 1.8 – 3.2

16. Ionic bonds • The electronegativity difference must be equal to or greater than __________. • Ionic bonds look like: • Na Cl

17. Opposite charges attract= electrostatic attraction Like the attraction of magnets Formula unit

18. Ionic compounds • Ionic bonds form ionic compounds. An ionic compound is composed of positive (cations) and negative (anions) ions that are combined so that the negative and positive charges are equal. • Note: Ionic compounds form lattice structures

19. Why do some atoms in formulas have subscripts and others do not? Use electron dot notation to show bonds and compounds Lewis structures

20. Ionic Bonds – Transfer of electrons • Show formula unit • Strength of bonds (bond energy)

21. Ionic Bonds & Compounds • Using electron dot to show the transfer of electrons • A metal must lose all its valence electrons • A non-metal must gain enough valence electrons to meet the Octet Rule. • Additional atoms (ions) of each type of element may be needed to form the correct compound.

22. Ionic Formula • Ionic formula units: The charges of the atoms in the compound must equal to zero. • Na ion (Na ) and Cl ion (Cl ) _______ + ________ = 0 Na ion (Na ) and Ca ion (Ca ) _______ + ________ = 0

23. Ionic compound names • Metal name + Non-metal (ide) • Prefix?? • Note: will practice names & formulas after determining bonds

24. Properties of Ionic Compounds

25. Video: Discovery Ed • Ionic bonds

26. Covalent Bond Non-metal and Non-metal Sharing of electrons to form a bond

27. Covalent Bonds • Bonds a ___________ to a ___________. • Valence electrons are __________ between a _________ and a _________.

29. Electronegativity Difference • The electronegativity difference must be equal to or less than _______. • It is a polar covalent bond if the difference is between __________. • It is a non-polar covalent bond if the difference is between ___________.

30. How do non-metals share electrons? • Sometimes equally • Sometimes unequally

31. Non-Polar Covalent Bond ∆EN= 0 – 0.3 The Electron pair that makes up the bond is shared evenly.

32. Non-Polar Covalent Bond

34. Polar Covalent Bond

35. Polar Covalent Bond∆EN = 0.4 – 1.7 The electron pair that makes up the bond is closer to the element that has the higher electronegativity.

36. Polar Covalent Bond

37. Covalent Bonds • Covalent bonds form covalent compounds, also called molecular compounds or molecules. Water Hydrogen Polarity: unequal distribution of charges One side: more negative, The other side: more positive

38. Covalent Bond- Sharing of electrons • Show bond pairs and lone pairs • Strength of bonds (bond energy) • Single, double and triple covalent bonds

39. Intermolecular forces • What holds the separate covalent bonds together? • http://www.northland.cc.mn.us/favicon.ico

40. Video: Discovery Ed – covalent bonds • Elements of chemistry: Compounds & Reactions

41. Metallic Bond Metal to Metal Electrons flow freely

43. Metallic Bonds • Bonds a _________ to a ____________. • The valence electrons ________ ______ and are not bonded to one atom. • The valence electrons from a ______ of ________.

44. Metallic bond: Sea of electrons The freedom of movement of the electrons in network of metals gives characteristic metallic properties: - - -

46. Bond typeCompound(names & formulas)Properties(physical and chemical)

47. Review • Metals __________ electrons because they have ________ electronegativity (EN) • Non-metals ________ electrons and have ________ electronegativity.

50. Ionic Bond