Download The Representative Elements

The Representative Elements
Ch 20
Representative Elements
• Their chemical properties are determined by
their valence (s and p) electrons.
• Properties are similar within a group, but first
element in a group tends to act differently
due to smaller size.
• Most abundant element is oxygen, followed
by silicon.
• Most abundant metals are aluminum and
iron, which are found as ores.
Group 1 (1A) – Alkali Metals
• Have Valence electron configuration
ns1
• Will lose 1 electron to form M+ Ions
• React vigorously with water to form M+
and OH- ions and hydrogen gas.
• React with oxygen to form oxides.
Lithium will form a regular oxide (Li2O)
while sodium will form a peroxide
(Na2O2). Potassium, rubidium and
cesium form superoxides (MO2)
Selected Reactions of the Alkali Metals
Reaction
Comment
2M + X2  2MX
X2 = any halogen molecule
4Li + O2  2Li2O
Excess oxygen
2Na + O2  Na2O2
M + O2  MO2
M = K, Rb or Cs
2M + S  M2S
6Li + N2  2Li3N
Li only
12M + P4  4M3P
2M + H2  2MH
2M + 2H2O  2MOH + H2
2M + 2H+  2M+ + H2
Violent reaction!
Hydrogen
• Can form covalent compounds with other
nonmetals.
• Will form salts, hydrides, with very active
metals (group 1A and 2A).
• Hydride ion, H-, is a strong reducing agent.
• Covalent hydrides form when hydrogen
bonds with other nonmetals.
• Metallic hydrides occur when hydrogen
atoms migrate into transition metal crystals.
Group 2 (2A) – Alkaline Earth Metals
• Have valence electron configuration ns2
• Called Alkaline earth because of the
basicity of their oxides.
• React less vigorously with water than
group 1.
• Heavier alkaline earth metals form ionic
nitrides and hydrides.
• Hard water is caused by the presence of
Ca+2 and Mg+2 ions.
Selected Reactions of the Alkaline Earth Metals
Reaction
Comments
M + X2  MX2
X2 = any halogen molecule
2M + O2  2MO
Ba gives BaO2 as well
M + S  MS
3M + N2  M3N2
High temperatures
6M + P4  2M3P2
High temperatures
M + H2  MH2
M = Ca, Sr or Ba; high temperatures; Mg
also needs high pressure
M + 2H2O  M(OH)2 + H2
M = Ca, Sr or Ba
M + 2H+  M+2 + H2
Be + 2OH- + 2H2O  Be(OH)42- + H2
Group 13 (3A)
• Have valence electron configuration ns2
np1
• Show increasing metallic character
going down the group.
• Boron forms covalent compounds with
hydrides called boranes. These
compounds are highly electron deficient
and very reactive.
• Aluminum has some covalent
characteristics as do indium and gallium.
• Thallium is completely metallic in
character.
Selected Reactions for Group 13 (3A) Elements
Reactions
Comments
X2 = any halogen molecule; Tl gives TlX
as well but no TlI3
2M + 3X2  2 MX3
High temperatures; Tl gives Tl2O as well
4M + 3O2  2M2O3
High temperatures; Tl gives Tl2S as well
2M + 3S  M2S3
M = Al only
2M + N2  2MN
2M +
6H+
2M +
2OH-

2M3+
M = Al, Ga or In; Tl gives Tl+
+ 3H2
+ 6H2O  2M(OH)4 + 3H2
-
M = Al or Ga
Group 14 (4A)
• Have valence electron
configuration ns2 np2
• Show a change from nonmetallic to
metallic properties going down the
group.
• All elements in this group form
covalent bonds with nonmetals.
• MX4 compounds (except
carbon)react with Lewis bases to
form two additional covalent
bonds.
Selected Reactions of the Group 14 (4A) Elements
Reactions
Comments
M + 2X2  MX4
X2 = any halogen molecule; M = Ge, or
Sn; Pb gives PbX2
M + O2  MO2
M = Ge, or Sn; high temperatures; Pb
gives PbO or Pb3O4
M + 2H+  M2+ + H2
M = Sn or Pb
Group 15 (5A)
• Have varied chemical properties.
• All members except nitrogen form
molecules with 5 covalent bonds.
(Nitrogen has no d sublevel)
• Nitrogen and Phosphorous are
nonmetals and form 3- anions in
salts with active metals.
• Antimony and bismuth are metallic.
However their 5+ cations tend to be
molecular rather than ionic.
Nitrogen
• The strength of the triple bond in the N2
molecule is important both thermodynamically
and kinetically as they decompose
exothermically.
• The nitrogen cycle is the process through which
nitrogen is recycled through the environment.
• Nitrogen forms a series of oxides in which it has
an oxidation state ranging from 1 to 5.
• Nitric acid is a strong acid which is important as a
reducing agent.
• Ammonia is the most important nitrogen hydride.
• Has pyramidal molecules with polar bonds.
• Hydrazine (N2H4) is a powerful reducing agent.
Phosphorous
• Exists in three elemental forms: white, black
and red.
• Phosphine (PH3) has a structure analogous to
that of ammonia but with bond angles closer
to 90o.
• Forms two oxides with oxidation states of 3+
and 5+.
Group 16 (6A)
• Shows the usual tendency of increasing
metallic properties going down the group.
• None behave as typical metals
• Achieve noble gas configurations by adding
two electrons to form 2- anions.
• Form covalent bonds with other nonmetals.
• Oxygen exists in two elemental forms: O2 and
O3.
• Sulfur has two elemental forms, both of which
contain stacks of S8 rings.
• Sulfur also forms two oxides: SO2 and SO.
• Sulfur forms a variety of compounds in which it
has a +6, +4, +2, 0 or -2 oxidation state.
Group 17 (7A) - Halogens
• This group consist of all nonmetals.
• Form hydrogen halides (HX) that behave as
strong acids in water, except for hydrogen
fluoride.
• Oxyacids of the halogens become stronger
as the number of oxygen atoms attached
to the halogen increase.
• Interhalogens are compounds of two
different halogens
• Halogen-carbon compounds are important
industrially: examples are Teflon, PVC and
the Freons.
Group 18 (8A) – Noble Gases
• Full valence shells ns2 np6
• Generally unreactive.
• Krypton, xenon and radon will
form compounds with the
highly electronegative
elements fluorine and oxygen.
Transition Elements
Ch 21
The last electron in transition metals occupy the d
sublevel. Because these inner orbitals cannot participate
as easily in bonding as the s and p orbitals the chemistry
is not greatly affected by the gradual change in the
increased number of electrons in the d orbital.
• Have metallic physical and chemical
properties.
• In forming ionic compounds with
nonmetals, the transition metals exhibit
several typical characteristics:
• More than one oxidation state is usually found
• Cations are often complex ions
• Most compounds are colored
• Most compounds have paramagnetic properties
• Transition metals form a variety of ions by
losing one or more of their electrons.
• The maximum possible oxidation state for a
given transition element corresponds to the
loss of all the s and d electrons.
• Transition metals form coordination
compounds which consist of complex ions
and counter ions.
• These coordination complexes are very
important to biological chemistry.
Naming Coordination Compounds
• The cation is named before the anion
• The ligands are named before the metal ion
• An o is added to the root name of an anion in the
ligand
• Prefixes are used to denote the number of simple
ligands
• The oxidation state of the central metal ion is
designated by a Roman numeral in parenthesis
• If more than one ligand is present, name them
alphabetically (prefixes do not count)
• If complex ion has a negative charge, the suffix
–ate is added to the name of the metal