Ch. 7 Ionic Bonding

1. Ch. 7 Ionic Bonding Chemistry

2. Homework • p. 193 #3-11, p. 207 - 208 # 31-32, 35-40, 55-56, 58-59, 62-63, 65 – DUE WEDNESDAY • p. 199 # 16, 18-20, p. 207-208 # 42,45 – DUE THURSDAY • Quiz over Table 7.2 on Wends, Nov 9 • Test over Ch. 7 on Tuesday, Nov. 15 (tentative)

3. Review • 1. What is an ion? • ion – an atom with a positive or negative charge (an electron has been lost or gained) 2. Where on the periodic table are the metals located? Nonmetals?

4. Valence Electrons • Core Electrons – “inner” electrons, do not participate in bonding • Valence Electrons – “outer” electrons, electrons in the highest occupied energy level • number of valence electrons largely determines the chemical properties of an element • So which electrons in an electron configuration are core and valence? Be – [He] 2s2 P – [Ne] 3s2 3p3 Core Valence Core Valence

5. So how do I find this valence number? • The valence electrons an atom has is the same as its group number for a representative (main group) element

6. So how do I find this valence number? • So how many valence electrons would Na have? • 1 • Iodine? • 7 • Krypton? • 8

7. How do I keep track of all these valence electrons? • Valence electrons are VERY important for chemistry and reactions! • Why? • Chemists have electron dot structures – diagrams that show valence electrons as dots

8. How do I keep track of all these valence electrons? • What do you notice about valence electrons down a group? • Electron configuration remains the same down a group, only the core electrons change

9. Practice • How many valence electrons does Al have? Draw the Lewis dot structure. • Electron configuration: • Valence Electrons: • Lewis dot structure: [Ne] 3s2 3s1 3

10. Crystal Structures • In crystalline materials, elements repeat in repetition to give a 3D arrangement known as a crystal lattice • A unit cell is the smallest part of the lattice that represents the entire lattice (repeated part) • 4 types of unit cells: • Primitive • Body-centered • Face-centered • Hexagonal close-packed

11. Crystal Structures Primitive body-centered Hexagonal close-packed face-centered

12. Part I: Metals Crystal coordination number (CN): number of neighbors to an atom in a unit cell Example: simple cubic is 6

13. Part I: Metals • Crystal coordination number (CN): number of neighbors to an atom in a unit cell • Face-centered: • 12 • Body-Centered: • 8 • Hexagonal: • 12

14. Let’s Think! • We know noble gases are very stable. How can we get the other elements to become stable like the noble gases? • Hint: Think of valence electrons!

15. Octet Rule • All elements want eight valence electrons (except H and He) • Why? • Achieve noble gas configuration, most STABLE • 2 electrons come from the ssubshell and 6 from the psubshell • Why can H and He NOT have eight valence electrons (Hint: they are considered stable with TWO valence electrons) • No psubshell!

16. Octet Rule • Elements will tend to gain or lose enough electrons to fulfill their octet • Will metallic elements gain or lose electrons? • Lose, much easier to lose electrons than gain electrons • Will nonmetallic elements gains or lose electrons? • Gain, much easier to gain electrons (can also share electrons)

17. Octet Rule • Metallic elements lose electrons • Why? • In simple terms…easier to lose than to gain to form the octet • Nonmetallic elements gain electrons • Why? • In simple terms, easier to gain a few electrons than lose them • Now let’s consider periodic trends! • Nuclear attraction across: • Shielding effect across: • Kinetic energy across: • This means: Increases across, nonmetals held tighter than metals Remains constant, does not offset nuclear attraction Remains constant Metals hold onto their electrons less tightly so it is easier for metals to lose their electrons. Additionally, nonmetals hold onto their electrons tighter . This trend, and the fact that nonmetals have higher electron affinity, means nonmetals tend to gain electrons.

18. Octet Rule • If metals lose electrons, they will form ions. Will these ions be negatively or positively charged? • If nonmetals gain electrons, will their ions be negatively or positively charged?

19. Octet Rule • Ions get special names to distinguish between those ions that are positively charged and those that are negatively charged • Cation – positively charged ion • Let’s try sodium! • Electron configuration: • Original electron dot diagram: • How many electrons will it lose? • New electron dot diagram: • New electron configuration [Ne] 3s1 1 Na+ [Ne]

20. Octet Rule • Ions get special names to distinguish between those ions that are positively charged and those that are negatively charged • Cation – positively charged ion

21. Octet Rule - Cations • Ions get special names to distinguish between those ions that are positively charged and those that are negatively charged • Cation – positively charged ion

22. I wonder… • Mg has the electron configuration of [Ne] 3s2. How many electrons would it lose or gain stability? • 2 • Will it take more or less energy to remove the second electron than the first electron? • Let’s use electron dot structures to show its loss of 2e-

23. Octet Rule - Cations • We just did one example of formation of a cation from Group 1 and Group 2. What can we say about the general formation of cations from Group 1 and the general fromation of cations from Group 2? • Group 1 – form +1 cation • Group 2 – form + 2 cation

24. What about those transition metals? • It’s extremely hard for transition metals to lose enough electrons to form a noble gas configuration. Why? • They would have to lose all the s and d electrons! • The transition metals ending with ns1(n-1)d10 can lose that 1s electron to achieve pseudo noble-gas electron configuration • What is one element that does this? • Elements with the configuration ns1(n-1)d5 can also lose that 1s electron to achieve half shell stability • What is one element that can do this?

25. What about those transition metals?

26. Octet Rule - Anions • Ions get special names to distinguish between those ions that are positively charged and those that are negatively charged • Anion – negatively charged ion • Let’s try chlorine! • Electron configuration: • Electron diagram: • How many electrons will it gain? • New electron diagram: • New electron configuration [Ne]3s23p5 1 Cl- [Ne]3s23p6

27. Octet Rule - Anions • Ions get special names to distinguish between those ions that are positively charged and those that are negatively charged • Anion – negatively charged ion

28. Octet Rule - Anions • Ions get special names to distinguish between those ions that are positively charged and those that are negatively charged • Anion – negatively charged ion

29. I wonder… • O has the electron configuration of [He] 2s2 2p4. How many electrons would it gain to gain stability? • 2 • Will it take more or less energy to gain the second electron than the first electron? • Let’s use electron dot structures to show its gain of 2e-

30. Octet Rule - Anions • How many electrons need to be gained by each group in group 5,6, and 7 to be stable?

31. Octet Rule

32. Common Ions • Everyone loves memorizing stuff in chemistry! Let’s memorize some more! • (Trust me, it’ll make your life 10x easier if you just memorize them now and get it over with!)

33. Common Ions

34. Let’s Think! • We all know that certain elements will bond together to form molecules, such as NaCl (table salt). Why is this? • Hint: Think of valence electrons.

35. Ionic Bonding • Ionic compound – composed of metal cations and nonmetal anions • They are still electrically neutral • Why? • The charges of the cation and anion cancel out • The negatively charged anion and the positively charged cation attract each other by electrostatic forces(force holding a cation and anion together due to their charge)

36. Ionic Bonding • Ionic compound – composed of metal cations and nonmetal anions • Let’s go back to the formation of NaCl… • What’s the electron configuration of Na? • Of Cl? • Their valence electrons can “add” together to form an ionic compound…now both elements are happy…just like Justin and Selena! [Ne] 3s1 [Ne] 3s23p5

37. Ionic Bonding • Ionic compound – composed of metal cations and nonmetal anions

38. Ionic Bonding • Ionic compound – composed of metal cations and nonmetal anions

39. Ionic Bonding • Ionic compound – composed of metal cations and nonmetal anions

40. Ionic Bonding • So Na+ and Cl- combine to form NaCl • NaCl is the chemical formula or a way to show the kinds and numbers of atoms in the smallest unit of a substance • So there is 1 Na+ for every 1 Cl- • What would Mg+2 and Cl-1 form? • There is 1 Mg+2 for every 2 Cl-1 so MgCl2 • Think of it this way: the charges have to become neutral

41. Ionic Bonding • The charges must become neutral • What about Sr+2and F-? • SrF2

42. Ionic Bonding • Another way to do it is balance out the charges • Ex: • 1 Mg has a +2 charge and 1 O has a -2 charge. The charges are already balanced! • So we have….MgO • What about…. • 1 Be has a +2 charge and 1 Br has a -1 charge. • How many Br will be needed to balance out the charges? • 2…so that gives us…. • BeBr2