Molecular Nitrogen \(N_2\) comprises about 78% by volume of Earth’s atmosphere. It occurs as Sodium nitrate, \(NaNO_3\)(chile saltpeter) & Potassium nitrate, \(KNO_3\)(Indian altpeter) in earth’s crust. Since nitrate are very soluble in water so these are not wide spread in the earth’s crust. Nitrogen is also an important constituent of amino acids, protein & nucleic acids in plants & animals.
Nitrogen shows anomalous behavior from rest of the elements due to following reasons;
Smaller size, high ionization enthalpy, high electronegativity & absence of d-orbital. It has unique ability to form p∏-p∏ multiple bonds with itself & with small size atoms like C & O as they have small size & high electronegativity. Heavier elements of this group do not form p∏-p∏ bonds as their atomic orbitals are so large & diffuse that they can’t have effective overlapping.
Thus Nitrogen exists as diatomic molecules \(N_2\) with a triple bond. Consequently, its bond enthalpy (941.4 KJ \(mol^{-1}\)) is very high. P, As & Sb form only single bonds as P-P, As-As & Sb-Sb. Due to much bond enthalpy N is much less reactive than P.
Single N-N bond is weaker than single P-P bond due to high interelectronic repulsion of the non bonding electrons, owing to small bond length. As a result, the catenation tendency is weaker in nitrogen. Hence nitrogen exists as gas while phosphorus exists as solid.
Nitrogen can’t form d∏- d∏ bond due to absence of d- orbitals so it can’t expand its covalency beyond four as heavier members can.
The following questions are multiple choice questions. choose the most appropriate answer.
1) Among group 15 elements which exists as gas at room temperature
a) Arsenic
b) Bismuth
c) Nitrogen
d) Phosphorous
2) The stability of +5 oxidation state decreases and that of +3 state increases down the group in group 15 elements due to
a) inert pair effect
b) decrease in ionisation enthalpy
c) increase in size
d) shielding effect
3) Nitrogen is restricted to a maximum covalency of 4 because of
a) absence of d-orbitals
b) presence of d-orbitals
c) absence of s and p-orbitals
d) none of the above
4) Extra pure \(N_2\) can be obtained by heating
a) \(NH_3\) with CuO
b) \(NH_4NO_3\)
c) \(\left(NH_4\right)_2Cr_2O_7\)
d) \(Ba\left(N_3\right)_2\)
5) Catenation tendency is weaker in nitrogen, because of
a) single N–N bond is weaker
b) single N–N bond is stronger
c) ability to form pi bonds by N atoms
d) none of the above
Group 16 elements are called chalcogens i.e., ore forming elements (oxygen, sulphur, selenium etc.) because most of the ores are oxides and sulphides. Oxygen is gas where as other elements of group 16 are solids. Oxygen shows anomalous behaviour. Oxygen is diatomic where is sulphur exists as \(S_8\) which has crown shaped structure. It shows allotropy. Sulphur is present in onion and garlic that is why they have pungent smell. Sulphur is used for manufacture of sulphuric acid which is called ‘King of chemicals’, used in fertilizer, detergents, dyes and drugs.
The following questions are multiple choice questions. Choose the most appropriate answer.
1) Group 16 elements are also known as
a) Noble elements
b) Halogens
c) Pnictogens
d) Chalcogens
2) Acidic character of hydrides of group 16 elements is in the order
a) \(H_2\)O < \(H_2\)S < \(H_2\)Se < \(H_2\)Te
b) \(H_2\)S < \(H_2\)Se < \(H_2\)Te < \(H_2\)O
c) \(H_2\)O < \(H_2\)Se < \(H_2\)Te < \(H_2\)S
d) \(H_2\)O < \(H_2\)S < \(H_2\)Te < \(H_2\)Se
3) Hybridisation of S in \(SF_4\) and geometry of \(SF_4\) are respectively
a) \(sp^3\)d, trigonal pyramidal
b) \(sp^3\)d, see saw
c) \(sp^3\), tetrahedral
d) \(dsp^2\), square planner
4) Which is not an acidic oxide?
a) \(CO_2\)
b) \(SO_2\)
c) \(Na_2\)O
d) \(Cl_2\)\(O_7\)
5) Which is not correct about allotropes of sulphur
a) The stable form at room temperature is rhombic sulphur
b) Monoclinic sulphur is stable above 369 K and transforms into rhombic sulphur below it
c) At 369 K both the forms are stable
d) Monoclinic sulphur is soluble in \(CS_2\) while rhombic sulphur not
Group 18 elements are called noble gases and not inert gases because compounds of Kr, Xe and Rn have been prepared. Their general electronic configuration is \(ns^2\)\(np^6\) except He(\(1s^2\) ). They have highest ionisation enthalpy and positive electron gain enthalpy due to stable electronic configuration. Helium is found in sun and stars. Noble gases have low boiling points due to weak van der Waals’ forces of attraction. Xenon forms \(XeF_2\), \(XeF_4\), \(XeF_6\), \(XeOF_4\), \(XeO_3\), \(XeO_2\)\(F_2\), their structures can be drawn on bases of VSEPR theory. Helium is mixed with oxygen by deep sea divers to avoid pain. Neon is used in coloured advertising lights. Argon is used in bulbs as inert gas. Kr and Xe are used in high efficiency lamps, head light of cars. Radon is radioactive formed by a-decay of Radium 226 88Ra Argon is most abundant (0.9%) noble gas in atmosphere.
The following questions are multiple choice questions. Choose the most appropriate answer.
1) What are the elements in group 18 (the far right) of the periodic table called?
a) Alkali metals
b) Alkaline earth metals
c) Halogens
d) Noble gases
2) Out of (i) \(XeO_3\) (ii) \(XeOF_4\) and (iii) \(XeF_6\) , the molecules having the same number of lone pairs on Xe are -
a) (i) and (ii) only
b) (i) and (iii) only
c) (ii) and (iii) only
d) (i) , (ii) and (iii)
3) Which one has linear shape?
a) \(XeF_2\)
b) \(XeF_4\)
c) \(XeF_6\)
d) \(XeO_3\)
4) Which of the outer electronic configuration represent Argon?
a) \(ns^2\)\(np^4\)
b) \(ns^2\)\(np^3\)
c) \(ns^2\)\(np^6\)
d) \(ns^1\)\(np^6\)
5) Which of the following statement is false?
a) Radon is obtained from the decay of radium
b) Helium is an inert gas
c) Xenon is the most reactive among the rare gases
d) The most abundant rare gas found in the atmosphere is helium
Assertion:-Nitrogen is restricted to a maximum covalency of 4.
Reason:-Nitrogen exists as a diatomic molecule (\(N_2\)) with a triple bond.
a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
c) Assertion is correct statement but reason is wrong statement.
d) Assertion is wrong statement but reason is correct statement.
Assertion:-The stability of hydrides decreases from \(NH_3\) to \(BiH_3\).
Reason:-There is a decrease in bond dissociation enthalpy of bond E-H from \(NH_3\) to \(BiH_3\). (E=Element of group 15)
a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
c) Assertion is correct statement but reason is wrong statement.
d) Assertion is wrong statement but reason is correct statement.
Assertion : -The bond between F-F is weaker than between Cl-Cl.
Reason:- Atomic size of F is smaller than that of Cl.
a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
c) Assertion is correct statement but reason is wrong statement.
d) Assertion is wrong statement but reason is correct statement.
Assertion:- \(H_2\)O is the only hydrides of the Chalcogens which is liquid.
Reason :- In ice each O atom is surrounded by 4H-atom.
a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
c) Assertion is correct statement but reason is wrong statement.
d) Assertion is wrong statement but reason is correct statement.
Assertion :- Nitrogen has higher ionisation enthalpy than that of oxygen.
Reason :- Nitrogen has smaller atomic size than that of Oxygen.
a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
c) Assertion is correct statement but reason is wrong statement.
d) Assertion is wrong statement but reason is correct statement.
Assertion :- Interhalogen compounds are more reactive than halogen.
Reason :- They all undergo hydrolysis giving halide, cation derived from the smaller halogen & anion derived from larger halogen.
a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
c) Assertion is correct statement but reason is wrong statement.
d) Assertion is wrong statement but reason is correct statement.
Assertion :-Solubility of noble gases in water decreases with increasing size of the noble gases.
Reason :- Solubility of noble gases in water is due to dipole- dipole interaction.
a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
c) Assertion is correct statement but reason is wrong statement.
d) Assertion is wrong statement but reason is correct statement.
Assertion :- \(O_3\) acts as a powerful oxidising agent.
Reason :- \(O_3\) oxidises lead sulphide to lead sulphate & iodide ions to iodine
a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
c) Assertion is correct statement but reason is wrong statement.
d) Assertion is wrong statement but reason is correct statement.
Assertion :-Water has high melting point.
Reason :- Water molecules are associated with hydrogen bonding.
a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
c) Assertion is correct statement but reason is wrong statement.
d) Assertion is wrong statement but reason is correct statement.
Assertion:-Ammonia gas is highly soluble in water.
Reason:-Its aqueous solution is weakly acidic.
a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
c) Assertion is correct statement but reason is wrong statement.
d) Assertion is wrong statement but reason is correct statement.
There is a considerable increase in covalent radius from N to P. However, from As to Bi only a small increase in covalent radius is observed. This is due to
a) Increase in number of shells
b) increase in valence electrons
c) increase in ionisation enthalpy
d) the presence of completely filled d and/or f orbitals