1IonsIons...

• 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.

3Which atoms gain or lose Which atoms gain or lose electrons?electrons?

• metals characteristically form cations -- they lose electrons.

• non-metals typically form anions -- they gain electrons if they form ions.

4Why 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.

5Examples...

Atoms in Group 1 form cations of +1 charge.

Li has configuration 1s2, 2s1.

Li loses the highest energy electron (from 2s energy):

Li --> Li+ + e-.

Li+ has configuration 1s2.

6Notice that the n =1 shell can Notice that the n =1 shell can have at most 2 electrons in it.have at most 2 electrons in it.

The n = 2 shell can have as The n = 2 shell can have as many as 8 emany as 8 e--. .

Easier for Li atom: lose 1 Easier for Li atom: lose 1 electron and have shell n =1 electron and have shell n =1 filled filled

Harder: gain 7 eHarder: gain 7 e-- to fill the n = 2 to fill the n = 2 shellshell

7Another example: SodiumAnother example: Sodium

Na is 1s2, 2s2, 2p6, 3s1.

Na --> Na+ + e-.

Na+ is 1s2, 2s2, 2p6.

The n =2 energy level is filled.

8In general...

• all elements in Group 1 have the valence configuration ns1.

• 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.

9All metals in Group 2 form +2 All metals in Group 2 form +2 cations:cations:

Mg is 1s2, 2s2, 2p6, 3s2.

To get a filled shell, easiest way is lose 2 e- from ns2 orbital:

Mg --> Mg+2 + 2e-.

Mg+2 is 1s2, 2s2, 2p6.

10The most general way to state the conclusion is this:

metals lose enough electrons to metals lose enough electrons to have the same configuration as have the same configuration as the nearest Noble Gasthe nearest Noble Gas.

Mg+2 and Na+ look like Ne.

Li+ looks like He.

11Transition metals (atoms in Groups 3-12) are more complicated...they often form more than one kind of cation. Examples:

Copper, Cu, forms both CuCopper, Cu, forms both Cu+1 +1

and Cuand Cu+2+2..

Iron, Fe, forms FeIron, Fe, forms Fe+2 +2 and Feand Fe+3+3. .

12Guess what? Metals in Group 13 Guess what? Metals in Group 13 lose 3elose 3e-- to form +3 cations: to form +3 cations:

Aluminum has configuration

1s2, 2s2, 2p6, 3s2, 3p1.

Al --> Al+3 + 3e-.

Al+3 is 1s2, 2s2, 2p6.

Al+3 looks like Ne.

13Metals 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.

14The 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 Instead, non-metals gain electrons to form ions.electrons to form ions.

15Review: which elements are non-which elements are non-metals? metals? atoms in Groups 14,15,16,17 above the diagonal connecting BBoron & Te Te (Tellerium).

Group 14: C (doesn’t form anion)

Group 15: N, P

Group 16: O, S, Se

Group 17: F, Cl, Br, I

16Can we predict charges of non-metallic anions? YES!

Group 15 elements form -3 Group 15 elements form -3 anions:anions:

N is 1s2, 2s2, 2p3.

N + 3e- --> N-3.

N-3 is 1s2, 2s2, 2p6.

The n = 2 shell is filled like Ne.The n = 2 shell is filled like Ne.

17Group 16 elements form -2 Group 16 elements form -2 anions:anions:

O is 1sO is 1s22, 2s, 2s22, 2p, 2p66..

O + 2eO + 2e-- --> O --> O-2-2..

OO-2 -2 is 1sis 1s22, 2s, 2s22, 2p, 2p66..

The n = 2 shell is filled. OThe n = 2 shell is filled. O-2 -2 looks looks like Ne.like Ne.

18Group 17 elements form -1 Group 17 elements form -1 anions:anions:

Br is [Ar] 4s2, 3d10, 4p5.

Br + 1e- --> Br -.

Br - is [Ar] 4s2, 3d10, 4p6.

Br Br -- looks like Kr looks like Kr.

19Ionic Compounds, Ionic Bonds

An ionic compound forms when An ionic compound forms when cations and anions associate with cations and anions associate with each othereach other: the opposite charges attract.

The electrostatic attraction of The electrostatic attraction of oppositely charged ions is an ionic oppositely charged ions is an ionic bond.bond.

20Formulas for Ionic Compounds

are easy to predict: the total + charge must = the total - charge. Examples:Examples:

NaNa++ and Cl and Cl-- combine 1:1 as NaCl. combine 1:1 as NaCl.

MgMg+2 +2 and Cland Cl-- combine 1:2 as combine 1:2 as MgClMgCl22..

21More examples...

AlAl+3 +3 and Br and Br -- combine 1:3 as AlBr combine 1:3 as AlBr33..

AlAl+3 +3 and Oand O-2 -2 combine 2:3 as Alcombine 2:3 as Al22OO33..

NaNa++ and S and S-2 -2 combine 2:1 as Nacombine 2:1 as Na22S.S.

Note: cation before anion

22Naming Ionic Compoundsis straight-forward:cation name, cation name, anion nameanion name.cation name cation name = name of metal element:NaNa++ is SodiumSodium (ion understood)

MgMg+2 +2 is MagnesiumMagnesium (ditto)

AlAl+3 +3 is AluminumAluminum (ditto)

23For cations that have more than one possible charge:

CuCu++ is Copper(I) Copper(I) [say “copper one”]

CuCu+2 +2 is Copper(II) Copper(II) [say “copper two”]

FeFe+2 +2 is Iron(II)Iron(II)

FeFe+3 +3 is Iron(III)Iron(III)

24anion name anion name = base name of element + ending “ide”

Examples:

ClCl- - is chlorine --> chloridechloride

OO-2 -2 is oxygen --> --> oxideoxide

NN-3 -3 is nitrogen --> nitridenitride

25Putting it all together...

Formula: Is Named:

FeBrFeBr33 iron(III) bromideiron(III) bromide

AlAl22OO33 aluminum oxidealuminum oxide

LiClLiCl lithium chloridelithium chloride

NaNa22SS sodium sulfidesodium sulfide

26

Ionic Solids

• • actually do not exist as actually do not exist as single unitssingle units

• • are large aggregates ofare large aggregates ofcations and anionscations and anions

27

• • each anion and cation may be each anion and cation may be associated with as many as associated with as many as

6 6 ions of opposite chargeions of opposite charge

• • the ions are stacked in the ions are stacked in layers much like fruit layers much like fruit piled up in the grocery storepiled up in the grocery store

28When 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.

29Example of NaCl

Cl-

Na+

Cl- Cl-

Cl-

Cl-

Cl-

Na+

Na+

Na+

Na+

Na+

part of a NaCl aggregate

H2Olots!

30Oxygen of H2O solvates cations

Na+ HO H O

H H

H H O H

O

H

31Hydrogen atoms of water Solvate Anions:

Cl- H-OHHO-H

H

OH

HO

H