Ions ... • are created when an atom gains or loses electrons;

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

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.

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.

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.

Examples... 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.

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

Another example: Sodium Na is 1s2, 2s2, 2p6, 3s1. Na --> Na+ + e-. Na+ is 1s2, 2s2, 2p6. The n =2 energy level is filled.

In 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.

All metals in Group 2 form +2 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.

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

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.

Guess what? Metals in Group 13 lose 3e- 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.

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.

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.

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

Can we predict charges of non-metallic anions? YES! Group 15 elements form -3 anions: N is 1s2, 2s2, 2p3. N + 3e- --> N-3. N-3 is 1s2, 2s2, 2p6. The n = 2 shell is filled like Ne.

Group 16 elements form -2 anions: O is 1s2, 2s2, 2p6. O + 2e- --> O-2. O-2 is 1s2, 2s2, 2p6. The n = 2 shell is filled. O-2 looks like Ne.

Group 17 elements form -1 anions: Br is [Ar] 4s2, 3d10, 4p5. Br + 1e- --> Br -. Br - is [Ar] 4s2, 3d10, 4p6. Br - looks like Kr.

Ionic Compounds, Ionic Bonds 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.

Formulas for Ionic Compounds 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 MgCl2.

More examples... Al+3 and Br - combine 1:3 as AlBr3. Al+3 and O-2 combine 2:3 as Al2O3. Na+ and S-2 combine 2:1 as Na2S. Note: cation before anion

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

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

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

Putting it all together... Formula: Is Named: FeBr3 iron(III) bromide Al2O3 aluminum oxide LiCl lithium chloride Na2S sodium sulfide

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

• 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

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.

Example of NaCl Na+ Cl- Na+ Cl- H2O Na+ Cl- Cl- Na+ lots! Cl- Na+ Na+ Cl- part of a NaCl aggregate

Oxygen of H2O solvates cations H H O H O H H O H Na+ O H H

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

Ions ... • are created when an atom gains or loses electrons;