Group 15 (N, P etc.) - Physical Properties

Question 1

Nitrogen has 2 electrons (saturated) in its penultimate shell. In accordance with Hund’s rule, electronic configurations involving fully filled or exactly half filled orbitals are most stable. Nitrogen behaves as a noble element under ordinary conditions

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Question 2

Metallic character increases as atomic number increases. N and P are purely non-metals. Sb and Bi are metals. Ar is a metalloid

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Question 3

N and P combine with electropositive elements to form nitrides and phosphides. Nitrides are more stable than phosphides. Bi and Sb form alloys with other metals

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Question 4

There is a gradual change in physical state of these elements under ordinary conditions. Nitrogen is a gas. Phosphorus, though a soft waxy solid, can readily pass into vapor state. Remaining elements are solids, are hard and possess metallic lustre

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Question 5

Atomic radii increase on going down the group due to addition of new energy shells. They are smaller than group 14 due to increased effective nuclear charge

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Question 6

Covalent radius considerably increases from N to P due to strong shielding effect of s and p electrons in inner shells. But from As to Bi, only small change is observed due to poor shielding effect of d and l or f electrons present in inner shells on valency electrons - this increases nuclear charge and reduces effect of addition of new energy shell to some extent

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Question 7

Ionization energy decreases down the group due to increase in atomic size. However they are higher than group 14 because of increased nuclear charge, reduced atomic radii and stable half-filled configurations -> more difficult to remove electron

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Question 8

Ionization energy of nitrogen very high due to its small size. N and P difference is high but differences between other consecutive members is small - due to less shielding effect of d-electrons in As and Sb, and f-electrons in Bi

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Question 9

Successive ionization energies increase as expected. E1 P > As > Sb > Bi

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Question 10

Electronegativity decreases gradually on descending the group from N to Bi. N is most electronegative and is a non-metal

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Question 11

Density increases gradually on descending the group

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Question 12

All elements except Bismuth show allotropy

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Question 13

Nitrogen exists in two solid allotropic forms, alpha nitrogen with cubic crystalline structure and beta nitrogen with hexagonal crystalline structure

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Question 14

Phosphorus exists in number of allotropic forms such as white, red, scarlet, alpha-black, beta-black and violet

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Question 15

Arsenic is known in 3 allotropic forms - grey, yellow and black. Antimony in 3 forms- yellow, black and explosive

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Question 16

Group 15 elements show catenation to a lesser extent than carbon because X-X bond strength is much lower than C-C bond.

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Question 17

Phosphorus has maximum tendency for catenation. N-N single bond is weak due to electronic repulsions between the lone pair of electrons on N atoms

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Question 18

Nitrogen is diatomic gaseous molecule at ordinary temperature - this is due to its ability to form multiple bonds - the molecule has 1 sigma and 2 pi bond.

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Question 19

Triple bond in N molecule is very stable and dissociation energy is very high - 225 kcal/mol. It is therefore inert under ordinary conditions

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Question 20

Phosphorus, arsenic and antimony exist as discrete tetraatomic tetrahedral molecules P4, As4, Sb4. Not capable of forming multiple bonds, angle between X-X-X is 60 and p-pi-p-pi bonding not possible

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Question 21

Bismuth involves purely metallic bonding

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Question 22

Maximum oxidation state of +5 by using all 5 electrons in outer shell

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Question 23

Tendency of the pair of ns electrons to remain inert (inert pair effect) increases with increase in atomic number. Thus only p electrons are used in bonding and +3 oxidation state is observed

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Question 24

+3 and +5 oxidation states of these elements are observed with halogens and sulphur

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Question 25

Stability of +3 increases and that of +5 decreases on moving down from N to Bi

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Question 26

N and P exhibit -3 oxidation state due to high electronegativity and small size. N forms N3- Nitride ion with highly electropositive elements. P forms P3- Phosphide ion to some extent. Tendency to show -3 oxidation state decreases from N to Bi (decreases from As to Bi due to inert pair effect as stability of +3 state increases from As to Bi)

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Question 27

Nitrogen exhibits large number of oxidation states from -3 to +5. -3 in NH3, -2 in NH2NH2, -1 in NH2OH, +2 in NO, +3 in N2O3, +4 in NO2, +5 in HNO3 and N2O5

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Question 28

All oxidation states of Nitrogen from +1 to +4 show disproportionation in acidic medium (redox reaction - Disproportionation is a specific type of redox reaction in which a species is simultaneously reduced and oxidised to form two different products). 3HNO2 (+3) ->HNO3 (+5) +2 NO (+2) + H2O

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Question 29

Phosphorus exhibits disproportionation in all intermediate oxidation states from -3 to +5 in acidic and basic mediums

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Question 30

Nitrogen forms trinegative ion M3-. It can achieve stable configuration by forming 3 single covalent bonds, by forming double or triple bonds, by tricovalent N as lewis base, and forming certain N compounds where valence shell is not complete but compounds are stable - NO, NO2 etc. These have unpaired electrons, are para-magnetic and have tendency to dimerise

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Question 31

Phosphorus attain stable configuration by sharing 3 p electrons and forming 3 covalent bonds..

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Question 32

Nitrogen never shows pentavalency. Max covalency of 4 when it donates the ns-electron pair to lewis acids and it doesnt possess d-orbitals in valence shell. Other elements have empty d-orbitals and can show covalency of 5 or 6 - PCl5, SbF6- etc.

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Question 33

N forms p-pi-p-pi multiple bonds with itself and with carbon and oxygen. Easily exists as triply bonded diatomic gaseous molecule at ordinary temp

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Question 34

P can form p-pi-d-pi but does not form many compounds like N (P2O, P2O3 etc. do not exist) as it cannot form p-pi-p-pi

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Question 35

P2O3 and P2O5 are known as dimeric oxides in the form P4O6 and P4O10

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Question 36

Thermal and electrical conductivity increases down the group. N and P are poor conductor, As is a semi conductor. Sb and Bi are good conductors

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Question 37

N forms 75% by mass and 78% by volume of atmosphere

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Question 38

P doesnt occur free in nature - 11th most abundant element. 60% of bones are Ca3(PO4)2 and average person has 3.5 kg of calcium phosphate. Present in DNA, RNA, ATP, ADP etc. and also found as phosphates in nature

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Question 39

As, Sb and Bi are not abundant. They occur as sulphides or oxides

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