Скачать или смотреть L2| Oxidation state and trends in chemical reactivity group 15 | p block | p Block Elements Class 12

L2| Oxidation state and trends in chemical reactivity group 15 | p block | p Block Elements Class 12

Unit 7: p Block Elements 👇👇👇
   • Chapter 7 : P Block Elements Class 12  
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In this video you will learn about Oxidation state and trends in chemical reactivity group 15 elements of p Block Elements class 12.
This video contains following topics at these time stamps-

00:00 P Block elements of class 12
00:05 Topics of covered in the video
00:47 Oxidation state of group 15 elements
28:25 Anomalous properties of nitrogen class 12
39:16 Reactivity towards hydrogen of group 15 elements
57:03 Reactivity towards oxygen of group 15 elements
01:01:01 Reactivity towards halogens group 15
01:06:50 Reactivity towards metals of group 15 elements

THEORY
7.1.7 Chemical Properties
Oxidation states and trends in chemical reactivity
The common oxidation states of these elements are –3, +3 and +5.
The tendency to exhibit –3 oxidation state decreases down the group due
to increase in size and metallic character. In fact last member of the group,
bismuth hardly forms any compound in –3 oxidation state. The stability
of +5 oxidation state decreases down the group. The only well characterised Bi (V) compound is BiF5. The stability of +5 oxidation state decreases and that of +3 state increases (due to inert pair effect) down the group. Besides +5 oxidation state, nitrogen exhibits + 1, + 2, + 4 oxidation states also when it reacts with oxygen. However, it does not form compounds in +5 oxidation state with halogens as nitrogen does not have d-orbitals to accommodate electrons from other elements to form bonds. Phosphorus also shows +1 and +4 oxidation states in some oxoacids.
In the case of nitrogen, all oxidation states from +1 to +4 tend to
disproportionate in acid solution.
Similarly, in case of phosphorus nearly all intermediate oxidation
states disproportionate into +5 and –3 both in alkali and acid. However
+3 oxidation state in case of arsenic, antimony and bismuth becomes
increasingly stable with respect to disproportionation.
Nitrogen is restricted to a maximum covalency of 4 since only four
(one s and three p) orbitals are available for bonding.
Anomalous properties of nitrogen
Nitrogen differs from the rest of the members of this group due to
its small size, high electronegativity, high ionisation enthalpy and
non-availability of d orbitals. Nitrogen has unique ability to form
pp -pp 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 pp -pp bonds as their atomic orbitals are so
large and diffuse that they cannot have effective overlapping.
Thus, nitrogen exists as a diatomic molecule with a triple bond (one
s and two p) between the two atoms. Consequently, its bond enthalpy
(941.4 kJ mol–1) is very high. On the contrary, phosphorus, arsenic
and antimony form single bonds as P–P, As–As and Sb–Sb while
bismuth forms metallic bonds in elemental state. However, the single
N–N bond is weaker than the single P–P bond because of high
interelectronic repulsion of the non-bonding electrons, owing to the
small bond length.
(i) Reactivity towards hydrogen: All the elements of Group 15
form hydrides of the type EH3 where E = N, P, As, Sb or Bi.
The stability of hydrides decreases from NH3 to BiH3 which can
be observed from their bond dissociation enthalpy.
Consequently, the reducing character of the hydrides increases.
Ammonia is only a mild reducing agent while BiH3 is the
strongest reducing agent amongst all the hydrides. Basicity also
decreases in the order NH3 PH3 AsH3 SbH3 BiH3. Due to
high electronegativity and small size of nitrogen, NH3 exhibits
hydrogen bonding in solid as well as liquid state.

(ii) Reactivity towards oxygen: All these elements form two types
of oxides: E2O3 and E2O5. The oxide in the higher oxidation state
of the element is more acidic than that of lower oxidation state.
Their acidic character decreases down the group. The oxides of
the type E2O3 of nitrogen and phosphorus are purely acidic,
that of arsenic and antimony amphoteric and those of bismuth
predominantly basic.
(iii) Reactivity towards halogens: These elements react to form two
series of halides: EX3 and EX5. Nitrogen does not form pentahalide
due to non-availability of the d orbitals in its valence shell.
Pentahalides are more covalent than trihalides. Since elements in +5 oxidation state will have more polarising power than in +3 oxidation state,
the covalent character of bonds is more in pentahalides. All the
trihalides of these elements except those of nitrogen are stable.
In case of nitrogen, only NF3 is known to be stable.

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