1 Ions Ions... are created when an atom gains or loses electrons; are chemical critters that have different numbers of protons and electrons.

2 Cations are ions that have a net + charge = > because there are more protons than electrons. Anions are ions that have a net - charge = > because there are more electrons than protons.

3 Which atoms gain or lose electrons? metals characteristically form cations -- they lose electrons. non-metals typically form anions -- they gain electrons if they form ions.

4 Why does it work this way? => there seems to be a natural drive for atoms to gain or lose enough electrons to end up with a filled shell (= energy level) of electrons.

5 Examples... Atoms in Group 1 form cations of +1 charge. Li has configuration 1s 2, 2s 1. Li loses the highest energy electron (from 2s energy): Li --> Li + + e -. Li + has configuration 1s 2.

6 Notice that the n =1 shell can have at most 2 electrons in it. The n = 2 shell can have as many as 8 e -. Easier for Li atom: lose 1 electron and have shell n =1 filled Harder: gain 7 e - to fill the n = 2 shell

7 Another example: Sodium Na is 1s 2, 2s 2, 2p 6, 3s 1. Na --> Na + + e -. Na + is 1s 2, 2s 2, 2p 6. The n =2 energy level is filled.

8 In general... all elements in Group 1 have the valence configuration ns 1. all elements in Group 1 lose this single valence electron to form a +1 cation, and all +1 cations in Group 1 have a filled (n-1) shell.

9 All metals in Group 2 form +2 cations: Mg is 1s 2, 2s 2, 2p 6, 3s 2. To get a filled shell, easiest way is lose 2 e - from ns 2 orbital: Mg --> Mg e -. Mg +2 is 1s 2, 2s 2, 2p 6.

10 The most general way to state the conclusion is this: metals lose enough electrons to have the same configuration as the nearest Noble Gas metals lose enough electrons to have the same configuration as the nearest Noble Gas. Mg +2 and Na + look like Ne. Li + looks like He.

11 Transition metals (atoms in Groups 3-12) are more complicated...they often form more than one kind of cation. Examples: Copper, Cu, forms both Cu +1 and Cu +2. Iron, Fe, forms Fe +2 and Fe +3.

12 Guess what? Metals in Group 13 lose 3e - to form +3 cations: Aluminum has configuration 1s 2, 2s 2, 2p 6, 3s 2, 3p 1. Al --> Al e -. Al +3 is 1s 2, 2s 2, 2p 6. Al +3 looks like Ne.

13 Metals vary in how easily they form cations: the Ionization Energy (IE) is the energy required to remove the first electron from an atom. Low IE = easily removed electrons. In any Group, IE decreases going down the column.

14 The element with the lowest IE of all the elements is in the bottom of Group 1 (Fr). Non-metals have very high IE values: it is hard to remove their electrons. Highest IE is for Fluorine. Instead, non-metals gain electrons to form ions.

15 which elements are non- metals? B Te Review: which elements are non- metals? atoms in Groups 14,15,16,17 above the diagonal connecting B oron & Te (Tellerium). Group 14: C (doesn’t form anion) Group 15: N, P Group 16: O, S, Se Group 17: F, Cl, Br, I

16 Can we predict charges of non-metallic anions? YES! Group 15 elements form -3 anions: N is 1s 2, 2s 2, 2p 3. N + 3e - --> N -3. N -3 is 1s 2, 2s 2, 2p 6. The n = 2 shell is filled like Ne.

17 Group 16 elements form -2 anions: O is 1s 2, 2s 2, 2p 6. O + 2e - --> O -2. O -2 is 1s 2, 2s 2, 2p 6. The n = 2 shell is filled. O -2 looks like Ne.

18 Group 17 elements form -1 anions: Br is [Ar] 4s 2, 3d 10, 4p 5. Br + 1e - --> Br -. Br - is [Ar] 4s 2, 3d 10, 4p 6. Br - looks like Kr Br - looks like Kr.

19 Ionic Compounds, Ionic Bonds An ionic compound forms when cations and anions associate with each other An ionic compound forms when cations and anions associate with each other: the opposite charges attract. The electrostatic attraction of oppositely charged ions is an ionic bond.

20 Formulas for Ionic Compounds Examples: are easy to predict: the total + charge must = the total - charge. Examples: Na + and Cl - combine 1:1 as NaCl. Mg +2 and Cl - combine 1:2 as MgCl 2.

21 More examples... Al +3 and Br - combine 1:3 as AlBr 3. Al +3 and O -2 combine 2:3 as Al 2 O 3. Na + and S -2 combine 2:1 as Na 2 S. Note: cation before anion

22 Naming Ionic Compounds is straight-forward: cation name, anion name cation name, anion name. cation name cation name = name of metal element: Na + Sodium Na + is Sodium (ion understood) Mg +2 Magnesium Mg +2 is Magnesium (ditto) Al +3 Aluminum Al +3 is Aluminum (ditto)

23 For cations that have more than one possible charge: Cu + Copper(I) Cu + is Copper(I) [say “copper one”] Cu +2 Copper(II) Cu +2 is Copper(II) [say “copper two”] Fe +2 Iron(II) Fe +2 is Iron(II) Fe +3 Iron(III) Fe +3 is Iron(III)

24 anion name anion name = base name of element + ending “ide” Examples: Cl - chloride Cl - is chlorine --> chloride O -2 --> oxide O -2 is oxygen --> oxide N -3 nitride N -3 is nitrogen --> nitride

25 Putting it all together... Formula:Is Named: FeBr 3 iron(III) bromide Al 2 O 3 aluminum oxide LiCllithium chloride Na 2 Ssodium sulfide

26 Ionic Solids actually do not exist as single units actually do not exist as single units are large aggregates of cations and anions are large aggregates of cations and anions

27 each anion and cation may be associated with as many as 6 ions of opposite charge each anion and cation may be associated with as many as 6 ions of opposite charge the ions are stacked in layers much like fruit piled up in the grocery store the ions are stacked in layers much like fruit piled up in the grocery store

28 When ionic compounds dissolve in a solvent such as water, the aggregation of cations and anions are broken up--- the compound dissociates into its constituent ions because the cations and anions are more highly attracted to the solvent than to each other.

29 Example of NaCl Cl - Na + Cl - Na + part of a NaCl aggregate H2OH2O lots!

30 Oxygen of H 2 O solvates cations Na+ H O H O H O H O H

31 Hydrogen atoms of water Solvate Anions: Cl - H-OH HO-H H OH HO H