Ions'''

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Ions... are created when an atom gains or loses
electrons are chemical critters that have
different numbers of protons and electrons.
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Cations are ions that have a net charge
gt because there are more protons than
electrons. Anions are ions that have a net
- charge gt because there are more electrons
than protons.
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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.
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Why does it work this way gt 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.
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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
--gt Li e-. Li has configuration 1s2.
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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
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Another example Sodium Na is 1s2 2s2 2p6
3s1. Na --gt Na e-. Na is 1s2 2s2
2p6. The n 2 energy level is filled.
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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.
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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 --gt Mg2
2e-. Mg2 is 1s2 2s2 2p6.
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The most general way to state the conclusion is
this metals lose enough electrons to have the
same configuration as the nearest Noble Gas. Mg2
and Na look like Ne. Li looks like He.
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Transition metals (atoms in Groups 3-12) are
more complicated...they often form more than one
kind of cation. Examples Copper Cu forms both
Cu1 and Cu2. Iron Fe forms Fe2 and Fe3.
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Guess what Metals in Group 13 lose 3e- to form
3 cations Aluminum has configuration 1s2 2s2
2p6 3s2 3p1. Al --gt Al3 3e-. Al3 is 1s2
2s2 2p6. Al3 looks like Ne.
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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.
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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.
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Review which elements are non-metals atoms in
Groups 14151617 above the diagonal connecting
Boron Te (Tellerium). Group 14 C (doesnt
form anion) Group 15 N P Group 16 O S
Se Group 17 F Cl Br I
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Can we predict charges of non-metallic anions
YES! Group 15 elements form -3 anions N is 1s2
2s2 2p3. N 3e- --gt N-3. N-3 is 1s2 2s2
2p6. The n 2 shell is filled like Ne.
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Group 16 elements form -2 anions O is 1s2 2s2
2p6. O 2e- --gt O-2. O-2 is 1s2 2s2
2p6. The n 2 shell is filled. O-2 looks like Ne.
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Group 17 elements form -1 anions Br is Ar 4s2
3d10 4p5. Br 1e- --gt Br -. Br - is Ar
4s2 3d10 4p6. Br - looks like Kr.
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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.
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Formulas for Ionic Compounds are easy to predict
the total charge must the total - charge.
Examples Na and Cl- combine 11 as NaCl. Mg2
and Cl- combine 12 as MgCl2.
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More examples... Al3 and Br - combine 13 as
AlBr3. Al3 and O-2 combine 23 as Al2O3. Na
and S-2 combine 21 as Na2S. Note cation before
anion
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Naming Ionic Compounds is straight-forward cation
name anion name. cation name name of metal
element Na is Sodium (ion understood) Mg2 is
Magnesium (ditto) Al3 is Aluminum (ditto)
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For cations that have more than one possible
charge Cu is Copper(I) say copper
one Cu2 is Copper(II) say copper
two Fe2 is Iron(II) Fe3 is Iron(III)
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anion name base name of element ending
ide Examples Cl- is chlorine --gt chloride O-2
is oxygen --gt oxide N-3 is nitrogen --gt nitride
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Putting it all together... Formula Is
Named FeBr3 iron(III) bromide Al2O3 aluminum
oxide LiCl lithium chloride Na2S sodium
sulfide
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Ionic Solids actually do not exist as
single units are large aggregates of cations
and anions
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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
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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.
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