p-block elements - e-CTLT

Report
Group 16 Elements
PREPARED BY
MR. AMULYA KUMAR SAMAL
PGT(CHEMISTRY)
KENDRIYA VIDYALAYA,KHANAPARA
GUWAHATI
PHONE NO.09706422596
[email protected]
OBJECTIVES:After studying this unit, the students will be able to :
1.appreciate general trends in the chemistry of
elements of groups 16
2.describe the properties of group-16.
3.Give answer the reasoning question.
The p-block elements
The p-block elements are placed in groups 13
to 18 of the periodic table.
Their valence shell electronic configuration
is ns2np1–6 (except He which has 1s2
configuration)
Group 16 Elements
Oxygen(O)
Non Metals
Phosphorus(S)
Selenium(Se)
Metalloids
Tellurium(Te)
Polonium(Po)
Typical
Metal
GROUP-16
Symbol
Atomic number
Electronic configuration
O
8
[He]2s22p4
S
16
[Ne] 3s23p4
Se
34
[Ar]3d10 4s2 4p4
Te
52
[Kr]4d10 5s2 5p4
Po
84
[Xe]4f145d106s26p4
Trends in properties
Electronic Configuration
The valence shell electronic configuration of
these elements is ns2np4.
The s orbital in these elements is completely
filled and p orbitals are four electrons .
Atomic and Ionic Radii
O
considerable
increase
S
Se
small increase
Te
Po
due to the presence of completely
filled d and/or f orbitals in heavier
members.sss
Ionisation Enthalpy Δi H
O
S
Se
Te
Δi H
Decreases.
Due to
gradual
increase in
atomic size
G-15
Δi H decreases
Because of the extra
stable half-filled p
orbitals electronic
configuration of
group-15
Po
ΔiH1 < ΔiH2 < ΔiH3
G-16
Electronegativity
O
3.50
S
2.44
Se
2.48
Te
2.01
Po
1.76
E.N Decreases.
Due to gradual
increase in
atomic size
Physical Properties
Oxygen and sulphur are non-metals,selenium
and tellurium metalloids, whereas polonium is
a metal
The melting and boiling points increase with an
increase in atomic number down the group. The
large difference between the melting and
boiling points of oxygen and sulphur may be
explained on the basis of their atomicity; oxygen
exists as diatomic molecule (O2) whereas sulphur
exists as polyatomic molecule (S8)
Chemical Properties
Oxidation states and trends in chemical
reactivity
The common o.s of these elements are –2, +4
and 6.
Group-15
Tendency to exhibit
–2 o.s decreases
due to increase in
size and metallic
character.
The stability of +6 o.s
decreases and that of +4
state increases (due to
inert pair effect) down
the group.
Since electronegativity of
oxygen is very high, it
shows only negative
oxidation state as –2
exceptin the case of OF2
where its oxidation state
is + 2.
Other elements of the
group exhibit + 2, + 4, +
6 oxidation states but + 4
and + 6 are more
common. Sulphur,selenium
and tellurium usually show
+ 4 oxidation state in their
compounds with oxygen
and + 6 with fluorine.
The stability of + 6 oxidation state decreases down
the group and stability of + 4 oxidation state increase
(inert pair effect). Bonding in +4 and +6 oxidation
states are primarily covalent.
Anomalous properties of oxygen
Reasons:
1.Its small size
2.high electronegativity
3.high ionisation enthalpy
4.non-availability of d orbitals.
Some anomalous properties of oxygen
1.State:
oxygen is a gas whereas the others elements
are solids and have allotropic forms.
2.Atomicity:
oxygen exists as diatomic molecule (O2) whereas
sulphur exists as polyatomic molecule (S8).
3.Ability to form pπ -pπ multiple bonds:
oxygen has unique ability to form pπ -pπ multiple bonds with
itself and with other elements having small size and high
electronegativity (e.g., C, O). Heavier elements of this group do
not form pπ -pπ bonds as their atomic orbitals are so large and
diffuse that they cannot have effective overlapping.
4) Reactivity towards hydrogen:
Their acidic character increases from H2O to
H2Te. The increase in acidic character can be
explained in terms of decrease in bond (H–E)
dissociation enthalpy down the group.
H2O < H2S < H2Se < H2Te (Acid Strength and
Reducing Character) --- BDE
H2Te < H2Se < H2S < H2O (Thermal
Stability) ---BDE
H2O < H2Te < H2Se < H2S (Volatility) --- H-Bond
and Van der waal’s force
H2S < H2Se < H2Te < H2O
(Boiling
Point) -- H-Bond and Vander waal’s force
Self Assesment
EXAMINATION DECODED
Important question with answer
Q.1# Thermal stability of water is much higher than that of H2S.
Ans:- Due to high bond dissociation enthalpy of O—H than S—H bond.
(2)Elements of group 16 generally show lower value of first ionization
enthalpy compared to the corresponding periods of group 15.
Ans: Due to extra stable half-filled p orbitals electronic configurations of
Group 15 elements, larger amount of energy is required to remove
electrons compared to Group 16 elements.
(3) Tendency to show –2 oxidation states diminishes from Sulphur to
polonium in group 16.
Ans:The outer electronic configuration of group 16 elements is ns2 np4.
These elements therefore have the tendency to gain two electrons to
complete octet. Since elctronegativity and I.E. decrease on going down the
group, tendency to show –2 oxidation state diminishes.
(4) Oxygen generally exhibit oxidation state of –2 only whereas
other members of the family exhibit +2, +4, +6 oxidation
states also.
Ans:Oxygen is a electronegative element thus exhibit oxidation
state of –2. .Other members of the family have d orbitals and
therefore, can expand their octets and show + 2, + 4, + 6
oxidation states also.
(5)There is large difference between the melting point of
Oxygen & Sulphur.
Ans:The large difference between the melting and boiling
points of oxygen and sulphur may be explained on the basis of
their atomicity; oxygen exists as diatomic molecule (O2)
whereas
sulphur exists as polyatomic molecule (S8).
(6) SF6 is known but SH6 is not known.
Ans: Because of very high ectronegativity
if fluorine , sulphur exhibits its maximum
oxidation stateof +6 in SF6. SH6 is not
formed because hydrogen is feebly
electronegative.
(7) SF6 is not easily hydrolysed.
Ans: Since sulphur is hexa-covalent it
cannot expand its covalency. . Sulphur
hexafluoride, SF6 is exceptionally stable
for steric reasons.

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