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. 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.

3. Chemical Bonding • Compounds: Definition: Properties of compounds: Compounds can be decomposed (separated) only by chemical means (not physical).

4. Chemical Bonds • Force between 2 atoms • Three bond types: • ________________________ • ________________________ • ________________________

5. 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.

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

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. 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)

12. Ionic Bond∆EN = 1.8 – 3.2

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

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

17. 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.

18. Why do some atoms in formulas have subscripts and others do not?

19. 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

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

21. Opposites Attract • Find ions that can bond • Write the symbol and the charge • Write the new compound formed by combining the ions. • Name the compound. • Write at least 15 compounds. • At least 10 should include subscripts.

22. Video: Discovery Ed • Ionic bonds

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

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

26. 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 ___________.

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

28. Non-Polar Covalent Bond

30. Polar Covalent Bond

31. 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.

32. Polar Covalent Bond

33. 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

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

35. Metallic Bond Metal to Metal Electrons flow freely

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

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

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

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

42. Warm-up: What type of bonds are created with: Ionic, Covalent (non-polar or polar) Use the PT (but not the electronegativity chart) • Cr and Fe • Rb and Br • Cl and Cl • H and F • Ba and I • S and S

43. Covalent Bonds – Strength • What is the • Relationship between: • Bond energy & • Bond length • Bond energy & • Number of bonds

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

45. Lewis structures:A different way • Practice Lewis structures (electron dot) • Structural formula (shows bonds with lines) • Introduce shape of compounds • VSEPR • Determine polarity • Identify diatomic molecules (7)

46. Electronic cereal: • Start with diatomic molecules • 2 atoms of the same element (7) • Rules to follow: Make every compound • Use different colors for each atom • Show how each atom contributes electrons to the bond and the lone pairs • Determine shape & polarity • Polarity is?

47. Electronic Cereal: F₂

48. Working with Moles Peer Tutoring: Working in pairs

49. Mole Flow Chart Mole

50. Mole Conversions (Factor Label Method) • Moles ↔ Grams Molar mass: 1 mole of = ? Grams