Transcript Oxygen

Chapter 18
 Oxygen
compounds are known of all
elements
 Except: He,Ne
 Oxygen
and possibly Ar
Chemisrty involves
 Obtaining Ne configuration by one of the
following means
 1.)
 2.)
Electron gain to form the Oxide O2Formation of 2 single bonds usually in
bent systems such as water or ethers.
 3.) Formation of a double bond (org.
Compounds)
 4.) Formation of a single bond, as well as
electron gain such as OH 5.) Formation of three covalent bonds such
as in H3O+
 6.) Formation in rare cases of 4 covalent
bonds
 Oxygen
has the possibility of a broad
range of bond types from ionic to
covalent, which is seen in the binary
oxides.
 Highly ionic ones  alakli and alkaline
earh metal oxides
 Completely covalent ones  CO2
 Intermediates  B,Al, Si
 Formation
of Oxide ion from Oxygen
requires 1000 kJ/mol.
 The
stability of ionic metal oxides comes
from the high lattice energies with the
small and highly charged oxide ion.
 Wen
the lattice energy is not sufficient to
offset the eneries for ionisation, oxides
with more covalent character are formed.
 Oxides
 BeO
 SiO2
 B2O3
with some covalent character.
 Covalent
oxides are compounds such as:
 CO2
 SO2
 SO3
 NO2
 Dominated
by Covalent bonding
 An important aspect of bonding of
molecular oxides is the use of p-orbitals
in π bonding wit other atoms.
 pπ-
pπ bonding is found in ketones (organic
compound)
 pπ-
dπ bonding is found in
 phosphine oxides (R3P=O)
 or
 linear M=O=M systems
 Terminal Oxygen atoms with 3 lone pairs
 (OH) These Oxygen atoms are sp3 hybridized
 Covalent
compounds with oxides with 2
lone pairs of electrons are typically
angular molecules.
 Water
(104.5˚)
 Alcohols
 Ethers
 Oxygen atoms are sp3 hybridized.
 Atoms
with d orbitals
 pπ –dπ is often present in the bond to
oxygen.
 Si-O-Si in quartz 142˚
 H3Si-O-SiH3
 Linear
is greater than 150˚
molecules are found in systems
with transition metals.
 The Oxonium Ion
 sp3 hybridized
 Oxonium
:OH3+
Ion formation is analogous to
the formation of ammonium ions.
 Oxygen is less basic than nitrogen,
oxonium ions are less stable.
 OH42+ is unlikely  repulsion towards
proton
 Oxonium ions undergo rapid inversion
 Basic
Oxides
 Dissolve
in dilute acids:
 Acidic
Oxides
 Covalent non metal oxides are acidic
 Unsoluble
oxides will dissolve in bases
 Amphoteric
 Other
 Redox
Oxides
Oxides
than acid-base
 Oxygen
has
 3 isotopes
 2allotropes (O2) and (O3)
 O2 is paramagnetic has a high
dissociation energy
 Ozone
 Is diamagnetic
 Electrical discharge produces Ozone
 Ozone
is an oxidizing agent.
 Oxidizing
Potential
 Colorless
Liquid
 Resembles water
 Igher hydrogen bound
 40% denser than water
 High Dielectric constant
 Strong oxidizing agent
 Heavy metal traces act as catalysts in
dissociation reactions
 In
dilute aqueous solutions:
 More acidic than water
 Production of peroxide:
 S,Se,Te,Po
have lower electronegativities
than oxygen
 Compounds less ionic
 Relative stabilities of bonds is different
 H-bonding is lower
 S---H--S bonds exist but are very weak
 Like all others S has dπ- pπ bonds
 SO42- has multiple dπ- pπ bonds.
 The
valence for S,Se,Te,Po is not confined
to 2, and d orbitals can be used to form
more than 4 bonds to other elements.
 SF6
 S has a strong tendency to catenation
 It forms polysulfide ions, polythionate
ions
 Changes
in properties from S to Po
 Size of atoms increase
 Electronegativity decreases
 1. The decreasing stability of the hydrides .
 2. The increasing tendency to form complex
ions such as SeBr62-.
 3. The appearance of metallic properties for
Te and Po atoms. Thus the oxides M02 are
ionic and basic, reacting with HCI to give
the chlorides.
 Sulfur
occurs widely in nature as the
element, as H 2S and S02, in metal sulfide
ores, and as sulfates [e.g., gypsum and
anhydrite (CaS04), magnesium sulfate,
and so on].
 Selenium
and tellurium are less abundant
but frequently occur as selenide and
telluride minerals in sulfide ores,
particularly those of Ag and Au.
 Polonium occurs in U and Th minerals as a
product of radioactive decay series. The
most accessible isotope, 21OpO (a, 138.4
days), can be made in gram quantities by
irradiation of Bi in nuclear reactors.
 On
melting, Ss first gives a yellow,
transparent, mobile liquid that becomes
dark and increasingly viscous above
about 160°C. The maximum viscosity
occurs about 200 °C, but on further
heating the mobility increases until the
boiling point (444.6 0C), where the liquid
is dark red.
 Sulfur
vapor contains S8 and at higher
temperatures S2 molecules. The latter,
like 02 are paramagnetic with two
unpaired electrons, and account for the
blue color of the hot vapor.
 The elements S, Se, and Te burn in air on
heating to form the dioxides; they also
react on heating with halogens, most
metals, and nonmetals. They are attacked
by hot oxidizing acids like H2S04or HNO3.
 The
S,Se and Te 2+ ions are square
All reactions of S8 must involve initial ring opening
to give sulfur chains or chain compounds. Many
involve nucleophilic reactants, for example,
 The
hydrides are extremely poisonous
gases with revolting odors. The toxicity of
H 2S far exceeds that of HCN. The thermal
stability and bond strengths decrease
down the series, whereas the acidity in
water increases.
 Hydrogen sulfide dissolves in water to give
a solution about 0.1 M at 1 atm.
 It
is a colorless fuming liquid (bp 80
degC) that is readily hydrolyzed as in
Reaction
 Since
the products are volatile it is used
to prepare IronChloride
 The
dioxides are obtained by burning the
elements in air. Sulfur dioxide is produced
when many sulfides are heated in air.
Selenium and tellurium dioxides are also
obtained by treating the elements with hot
nitric acid to form H2Se03and 2 Te02·HN03
heating these drives off water or nitric
acid.
 Sulfur
dioxide has lone pairs and can act
as a Lewis base. However, it also acts as a
Lewis acid giving complexes, for
example, with amines, as in (CH3hNS02
and with electron-rich transition metal
complexes.
 Sulfur
dioxide is quite soluble in water;
such solutions, which possess acidic
properties, have long been referred to as
solutions of sulfurous acid, H2S03
 Sulfur
trioxide is obtained by reaction of
S02 with 02 reaction needs a catalyst such
as platinum sponge, V205 or N0.
 Sulfur trioxide reacts vigorously with
water to form sulfuric acid.
 Industrially, S03 is absorbed in
concentrated H2S04 to give oleum , which
is then diluted.