Transcript Slide 1

Important reminder!
Midterm is Friday, March 24
Chapters 5-8 (except today’s material)
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Group 1A elements (ns1, n  2)
M
M+1 + 1e-
2M(s) + 2H2O(l)
2M2O(s)
metal oxides
Increasing reactivity
4M(s) + O2(g)
2MOH(aq) + H2(g) metal hydroxides
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Alkali Metals
• Alkali metals (except Li) react with oxygen to
form peroxides (O22- anion):
2Na + O2  Na2O2
• K, Rb, and Cs also form superoxides (O2- anion):
K + O2  KO2
• Alkali metal ions colorless, but produce bright
colors when placed in flame.
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Group 2A elements (ns2, n  2)
M
M+2 + 2e-
Be(s) + 2H2O(l)
Mg(s) + 2H2O(g)
M(s) + 2H2O(l)
No Reaction
Mg(OH)2(aq) + H2(g)
M(OH)2(aq) + H2(g) M = Ca, Sr, or Ba
Increasing reactivity
BeO and MgO form at elevated temperatures; CaO, StO, and BaO form at rt.
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Alkaline earth metals
• Be does not react with
water, Mg reacts only
with steam, but others
react readily with
water.
• Reactivity tends to
increase as go down
group.
Mg(s) + 2H2O(l)
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Mg(OH)2(aq) + H2(g)
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Group 3A elements (ns2np1, n  2)
B is a metalloid; boron does not form binary ionic compounds and is unreactive
toward O2 and H2O.
Al is most abundant metal in Earth’s
rest of Group 3A are metals
crust, found as aluminosilicates.
4Al(s) + 3O2(g)
2Al(s) + 6HCl(aq)
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2Al2O3(s)
Bauxite is chief ore of Al.
2AlCl3(s) + 3H2(g)
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Group 3A elements (ns2np1, n  2)
Aluminum forms only tripositive ions.
Other 3A elements form both +3 and +1 states with +1 becoming more stable
going down the group
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Thermite reaction
2Al(s) + Fe2O3
Al2O3(l) + 2Fe(l)
ΔH= -847.6 kJ/mol
Enough heat released to raise the temperature to ~3000 oC which causes
the products to be molten.
This reaction is often used to weld iron and steel (alloys of Fe) parts together.
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Booster rockets
10Al(s) + 6NH4ClO4
4Al2O3(l) + 2AlCl3(l) + 12H2O(g) + 3N2(g)
Enough heat released to raise the temperature to 3200 oC which causes
2 gases to expand rapidly.
The expanding water vapor and nitrogen lift the rocket boosters with a
tremendous force. All the fuel is burned in about two minutes.
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Group 3A elements (ns2np1, n  2)
Aluminum forms only tripositive ions.
Other 3A elements form both +3 and +1 states with +1 becoming more stable
going down the group
Metallic elements also form many molecular compounds.
AlH3 resembles BeH2 (diagonal relationship, gradual shift from metallic
to nonmetallic character from left to right across the periodic table.
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Group 4A elements (ns2np2, n  2)
C nonmetal, Si & Ge metalloids, Sn & Pb metals
Sn(s) + 2H+(aq)
Sn2+(aq) + H2 (g)
Pb(s) + 2H+(aq)
Pb2+(aq) + H2 (g)
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Group 4A elements (ns2np2, n  2)
4A elements form compounds in +2 and +4 oxidation states.
For C and Si, +4 oxidation state is more stable.
CO2 more stable than CO
SiO2 exists; SiO does not (under normal conditions)
+4 is only slightly more stable for Sn; +2 is more stable for Pb
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Group 5A elements (ns2np3, n  2)
N & P nonmetals, As & Sb are metalloids, Bi is a metal
Elemental N exists as N2
NO, N2O, NO2, N2O4, and N2O5
N accepts 3 e- to form nitride, N3- (most metallic nitrides
are ionic compounds)
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Group 5A elements (ns2np3, n  2)
P exists as P4 molecules, forms P4O6 and P4O10
2 important oxoacids:
N2O5(s) + H2O(l)
P4O10(s) + 6H2O(l)
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2HNO3(aq)
4H3PO4(aq)
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Group 6A elements (ns2np4, n  2)
O, S, Se nonmetals; Te, Po metalloids
O exists as O2
S and Se are S8 and Se8
O, S, Se, Te form dianions by accepting 2 eO forms a large number of molecular compounds with
nonmetals
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Oxygen
• Two allotropes:
– O2
– O3, ozone
• Three anions:
– O2−, oxide
– O22−, peroxide
– O21−, superoxide
• Tends to take
electrons from other
elements (oxidation)
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Group 6A elements (ns2np4, n  2)
Important compounds of S are SO2, SO3, and H2S.
Formation of sulfuric acid:
SO3(g) + H2O(l)
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H2SO4(aq)
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Group 7A elements (ns2np5, n  2)
All halogens are nonmetals and exist as X2
4HF(aq) + O2(g)
Increasing reactivity
2F2(g) + 2H2O(l)
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Halogens
• Large, negative electron
affinities
– Therefore, tend to oxidize
other elements easily
• React directly with metals
to form metal halides
• Chlorine added to water
supplies to serve as
disinfectant (HOCl)
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Group 7A elements (ns2np5, n  2)
Halogens have high IE and large negative EA
X + 1eX2(g) + H2(g)
X-1
(halides)
2HX(g)
Increasing reactivity
Form ionic compounds with alkali and alkali earth metals
Form molecular compounds among themselves (ICl, BrF3)
and with nonmetals (NF3, PCl5, and SF6)
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Group 7A elements (ns2np5, n  2)
X2(g) + H2(g)
2HX(g)
(when X=F, explosive)
Increasing reactivity
Hydrogen halides dissolve in H2O to form hydrohalic acids
HF is a weak acid (weak electrolyte)
HCl, HBr, HI strong acids (strong electrolytes)
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Group 8A elements (ns2np6, n  2)
Completely filled ns and np subshells. Highest
ionization energy of all elements.
No tendency to accept extra electrons.
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Noble, but not completely inert
• Xe forms three
compounds:
– XeF2
– XeF4 (at right)
– XeF6
• Kr forms only one
stable compound:
– KrF2
• The unstable HArF was
synthesized in 2000.
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Properties of oxides across a period
basic
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acidic
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Properties of oxides across a period
basic
acidic
Classified as acidic or basic depending on whether they produce acids or
bases when dissolved in water.
Na2O(s) + H2O(l) -> 2NaOH(l)
Classified as acidic or basic depending on whether they react with
acids or bases in certain processes.
Al2O3(s) + 6HCl(aq) -> 2AlCl3(aq) + 3H2O(l)
Al2O3(s) + 2NaOH(aq) + 3H2O -> 2NaAl(OH)4(aq)
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Properties of oxides across a period
basic
acidic
Classified as acidic or basic depending on whether they produce acids
or bases when dissolved in water.
Classified as acidic or basic depending on whether they react with
acids or bases in certain processes.
CO & NO are neutral; they do not react with H2O to produce an acidic
or basic solution.
As the metallic character of the elements decreases from left to
right across the period, their oxides change from basic to amphoteric
to acidic.
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