Dr Nouf H Alotaibi Pblock Elements V A elements General trend Electron configurations ns 2 np 3 n is the period number The s orbital is completely filled and p orbital is half filled which makes them stable ID: 918933
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Slide1
P-block Elements
V A elements (Group 15)
Dr.
Nouf
H. Alotaibi
Slide2P-block Elements- V A elements
General trend
Electron configurations ns
2
np3 (n is the period number)The s orbital is completely filled and p orbital is half filled which makes them stable.Oxidation states that range from -3 to +5.The chemical properties of these elements are determined by the oxidation states exhibited by them.Electronegativity decreases down the group.Ionization energy decreases down the group.The metallic character of the group increases down the group.Atomic radii increase in size down the group. Electron affinity decreases down the group.Melting point increases down the group.Boiling point increases down the group.
Nitrogen
)
N
(
,
P
hosphorus
(P),
Arsenic
(As
),
Antimony
(Sb), and
Bismuth
(Bi),
Slide3P-block Elements- V A elements
As we move down the group, there is a transition from non-metallic to metallic through metalloid character.
Nitrogen and phosphorus, are
nonmetals
; The remaining three members, arsenic (As), antimony (Sb), and bismuth (Bi), have some metallic character.Two of the most dissimilar nonmetallic elements are in the same group: reactive phosphorus and unreactive nitrogen.There is no clear division of properties between non-metals and metals in this group.The melting and boiling points are a good indication between metals and semimetals.General trend
Slide4P-block Elements- V A elements
Element Melting point (°C) Boiling point (°C) N2
-
210
-196 P4 44 281 As Sublimes at 615 Sb 631 1387 Bi 271 1564Melting and boiling points of the Group 15 elementsThe melting and boiling points increase down the group, except for a decrease in melting point from Sb to BiFor the alkali metals, the melting points of main group metals tend to decrease down a group, whereas those of nonmetals tend to increase down a group.Thus, the increase-decrease pattern indicates that the elements nitrogen and phosphorus are non-metals, arsenic and antimony are metalloids and bismuth is a typical metal.General trend
Slide5P-block Elements- V A elements
General trend
The Electronegativity Difference of Nitrogen and Phosphorus
N has a much higher electronegativity than the other members of Group 15. As a result, the polarity of the bonds in N compounds is often the reverse of that in P and the other heavier members of the group.For example, the different polarities of the N—Cl and P—Cl bonds result in different hydrolysis products of the respective trichlorides:NCl3(l) + 3 H2O(l) NH3 (g) + HClO(aq)PCl3
(l
) + 3 H
2
O(
l
)
H
3
PO
3
(aq) + 3 HCl(aq)Because the nitrogen-hydrogen covalent bond is strongly polar, ammonia is basic, whereas the hydrides of the other Group 15 elements; phosphine, PH3, arsine, AsH3, and stibine, SbH3 are essentially neutral.
Element
Electronegativity
N 3.0
P 2.1
As 2.0
Sb 1.9
Bi 1.9
Slide6P-block Elements- V A elements
General trend
Oxidation State and Chemical Properties
The elements of group 15 generally exhibit -3, +3 and +5 oxidation states. The tendency to exhibit -3 oxidation state decreases as we move down the group. due to increase in the size of the atom and the metallic character. Bismuth hardly forms any compound in oxidation state -3.The stability of +5 state also decreases as we move down the group. BiF5 is the only well characterized Bi(V) compound.
Slide7P-block Elements- V A elements
General trend
Oxidation State and Chemical Properties
Due to inert pair effect, the stability of +5 state decreases and +3 state increases as we move down the group in the periodic table. Nitrogen reacts with oxygen and also exhibits +1, +2, +4 oxidation states. On the other hand phosphorus shows +1 and +4 states in some oxoacids* (H3PO2, H4P2O6).
Nitrogen has only 4
electrons
in its outermost shell (one
in s orbital and
3
in p
) which is available for bonding, hence it exhibits a maximum covalence of 4.
The heavier elements have a vacant d orbital in the valence shell which is used for bonding.
*oxoacids is the acids that contain oxygen
Slide8P-block Elements- V A elements
General trend
Oxidation State and Chemical Properties
Consequences of inert-pair effect:Nitrogen compounds disproportionate in acid solutions.*Disproportionation reactions: Redox reactions in which the oxidizing agent and the reducing agent are the same speciesSimilarly, in case of phosphorus nearly all intermediate oxidation states disproportionate into +5 and –3 both in alkali and acid. But the +3 oxidation state in case of arsenic, antimony and bismuth becomes stable and do not ungergo disproportionation. 3HNO2 HNO3 + H2O + 2NO
Reduction
Oxidation
Slide9P-block Elements- V A elements
Group 15 hydrogen compounds
NH
3
PH3 AsH3 SbH3 BiH3 decreasing basicity decreasing stability A-H bond strength 391 322 247 255 The nitrogen hydrogen compounds are much more stable that all of the other hydrogen compounds formed by the members of Group 15.
Slide10P-block Elements- V A elements
N-X
π bonding important
3- and 2-coordination is common in multiple bonding to X = N, C, O
P-X pπ-pπ bonding is weak3 single bonds + lone-pair or 4 single bonds (cation) both common. Example:N2 vs. P4 or other forms of phosphorus, or AsGroup 15 compounds with X = N, C, O
Slide11P-block Elements- V A elements
Halogen compounds of Group 15
Halides are formed by direct combination of the elements:
NF
3 is stable, NCl3 is reactive (bleach for flour), neither is very basic. (NH4Cl + 3Cl2 = NCl3 + 4HCl) Halides of P, As, and Sb are important laboratory chemicals: AX3 and AX
5
forms are both important.
PCl
3
and PBr
3
are reactive and useful as starting materials to other P-containing compounds.
PF
3
more stable.
PF
5, PCl5, AsF5, SbF5, SbCl5 are strong Lewis acids.
2
A
(s
)
+ 3X
2
2
AX
3
(A
= all except N)
AX
3
+ X
2
AX
5
(A
= all except N and Bi)
Slide12P-block Elements- V A elements
Nitrogen
Rare in the Earth’s crust but it is the principal component of our atmosphere (76% by mass)
N≡N triple bond strength is 944 kJ·mol-1 making it almost as inert as the noble gases. N is used in medicines, fertilizers, explosives, and plastics.The biggest commercial use for elemental nitrogen gas is for the formation of ammonia in the Haber process.N has a wide range of oxidation numbers. Nitrogen compounds are known to have every whole number oxidation number from -3 to +5. In addition, some fractional oxidation numbers are known to exists. N can only form up to four bonds
Slide13P-block Elements- V A elements
The triple nitrogen-nitrogen bond energy is greater than that for the triple carbon-carbon bond.
Conversely, the single bond between two nitrogen atoms is much weaker than the carbon-carbon single bond. It is this large difference between N
N and NN bond strengths (742 KJ/mol) that contributes to the preference in N chemistry for the formation of the dinitrogen molecule in a reaction rather than chains of nitrogen-nitrogen single bonds, as occurs in carbon chemistry. Furthermore, the fact that dinitrogen is a gas means that an entropy factor also favors the formation of the dinitrogen molecule in chemical reactions. Bond energy Bond energyNitrogen bonds (kJ/mol) Carbon bonds (KJ/mol)NN 247 CC 346NN 942 CC 835
Slide14P-block Elements- V A elements
Phosphorus
The radius of phosphorus is nearly 50% bigger than that of nitrogen. Thus P is too big to approach each other close enough for their 3
p
orbitals to overlap and form π bondsThe availability of the 3d orbitals means that phosphorus can form as many as six bonds.It has two allotropes; white and red.P4 molecule found in white phosphorous while red phosphorous appears as a chain structure. White Red
Slide15P-block Elements- V A elements
Phosphorus
Condensed phosphorus vapor is called white phosphorus and is a soft, white, poisonous, molecular solid consisting of tetrahedral P
4
molecules. White phosphorus is highly reactive.White phosphorus changes to red phosphorus (amorphous network) when heated in the absence of air. Red phosphorus is much less reactive.Red phosphorus is used in the striking surfaces of matchbook because he phosphorus ignites with friction.White phosphorous reacts vigorously with the oxygen in air and inflames in air at only 35° C so must be stored under water. Red
phosphorus is stable in air.
https
://
youtu.be/ch3jwHZw5nE
Phosphates
(
PO
4
3-
) and phosphoric acid (
H
3PO4) are the most common compounds of phosphorus.
Slide16P-block Elements- V A elements
The higher oxidation states of nitrogen are strongly oxidizing in acidic solution, those of phosphorus are quite stable.
In general, the highest oxidation state of P (+5) is the most thermodynamically stable and the lowest oxidation state (-3), the least stable, the opposite of N.
Contrasts in the Chemistry of Nitrogen and Phosphorus
Slide17P-block Elements- V A elements
Contrasts in the Chemistry of Nitrogen and Phosphorus
N
2
is the stable form for the element.* due to the very high strength of the N-N triple bond compared to the single (or double) bonds.Elemental phosphorus contains groups of singly bonded phosphorus atoms (P4).there is a much smaller difference between the single and triple bond energies, compare to the large difference between N‚N and NN bond strengths (742 KJ/mol).N is very stable to oxidation, P reacts vigorously with oxygen to give oxides.due to the strength of phosphorus-oxygen single bond Bond energy Bond energyNitrogen bonds (kJ/mol) Phosphorus bonds (kJ/mol)N
N 247 P
P 200
N
N 942 P
P 481
N
O 201 P
O 335* N2 is a common product from nitrogen-containing compounds in chemical reactions
Slide18P-block Elements- V A elements
N
2
H
4 (hydrazine)Hydrazine is a fuming, colorless liquid.It is a weak base.Hydrazine is a strong reducing agent.Uses:Rocket Fuel, Most of the 20K tonnes produced worldwide annually is used as the reducing component of a rocket fuel, usually in the form of asymmetrical dimethylhydrazine, (CH3)2NNH2. Remove dissolved corrosive oxygen from water
The structure of hydrazine is like that of ethane, except that two ethane hydrogens are replaced by lone pairs of electrons, one pair on each nitrogen atom.
Molecular structure of hydrazine (N
2
H
4
)
Slide19P-block Elements- V A elements
NH
3
(ammonia)
NH3 is a reasonably strong Lewis baseNH3 salts decompose when heatedSome laboratory ways to make ammonia:6 Li + N2 2 Li3N 6 Li(OH) + NH3 6 Al + N2 2 AlN Al(OH)3
+ NH3
Industrial
method: Haber process (Fe/Fe
3
O
4
catalyst). More moles of NH
3
produced than any other industrial chemical.
NH
3 has some similarities to water, but is less polarSchematic diagram of the Haber process for the manufacture of NH3
.
H
2
O
H
2
O
Nitrogen Compounds
Slide20P-block Elements- V A elements
Azide
ion (N
3
- )Highly reactive polyatomic anionIts most common salt is sodium azide (NaN3) Like most of the azide salts, NaN3 is shock sensitive NaN3 is used in airbags where it decomposes to elemental sodium and nitrogen when detonated2NaN3 (s) 2Na(s) + 3N2 (g)
The
azide
ion is a weak base and accepts a proton to from its conjugate acid,
hydrazoic
acid (HN
3
) which is a weak acid.
N
3
-
Lewis Structure
https://www.youtube.com/watch?v=KLY7b8Fglv0https://www.youtube.com/watch?v=eT0xWRFGB78Nitrogen IonsNitrogen Compounds
Slide21P-block Elements- V A elements
PH
3
(phosphine)
PH3 is much less soluble than ammonia in water because PH3 can not form hydrogen bonds to water.Aqueous solutions of PH3 are neutral because the electronegativity of phosphorus is so low that the lone pair of electrons on PH3 is spread over the hydrogen atoms as well as the phosphorus atomPH3 is a very weak acidProperties:Poisonous GasBurst into flame in air if it is slightly impure
Slide22P-block Elements- V A elements
Hydrogen
Azide
It is a
colorless liquid, is quite different from the other nitrogen hydrides. It is acidic, with a pKa similar to that of acetic acid:HN3(aq) + H2O(l) H3O-(aq
) + N3
+
(
aq
)
It is highly explosive, producing hydrogen gas and nitrogen gas:
2 HN
3
(
l
)
H2(g) + 3 N2(g)Nitrogen Compounds
Slide23P-block Elements- V A elements
Nitrides (solids that contain the nitride ion
(N
3-
)The combination of dinitrogen on heating with the Group 2 metals and lithium and Aluminium to form ionic nitrides, containing the N3- ion. The reaction with lithium is6 Li(s) + N2(g) → 2 Li3N(s) Nitrides are only stable for small cations such as lithium or magnesiumMost nitrides dissolve in water to produce ammonia and the corresponding hydroxideExample:
Mg
3
N
2(s)
+ 6H
2
O
(l)
3Mg(OH)
2(s)
+ 2NH3(g)
Slide24P-block Elements- V A elements
Nitrogen Oxide and Oxoacids
Nitrogen forms an excess of common oxides:
dinitrogen oxide, N
2O; nitrogen monoxide, NO; dinitrogen trioxide, N2O3; nitrogen dioxide, NO2; dinitrogen tetroxide, N2O4; and dinitrogen pentoxide, N2O5. In addition, there is nitrogen trioxide, NO3, commonly called the nitrate radical, which is present in tiny but essential proportions in the atmosphere. Each of the oxides is actually thermodynamically unstable with respect to decomposition to its elements, but all are kinetically stabilized.
Almost all nitrogen oxides are acidic
Some are acid anhydrides (a compound that forms an oxoacid when it reacts with water)
Slide25P-block Elements- V A elements
Nitrogen Oxide and Oxoacids
Slide26P-block Elements- V A elements
Nitrogen Oxide and Oxoacids
NO (nitrogen oxide, nitrogen monoxide, or nitric oxide)
NO is produced from hot airplane and automobile engines;
It has many harmful effects: leads to acid rain, formation of smog, as well as contributes to the destruction of the ozone layerNO is rapidly oxidized to NO2 on exposure to air2NO(g) + O2(g) 2NO2 (g) The NO2 then reacts with water, forming acid rain
NO also plays beneficial roles in small amounts. In the body it acts as a neurotransmitter and helps to dilate blood vessels and participates in other physiological changes.
Slide27P-block Elements- V A elements
Nitrogen Oxide and Oxoacids
NO
2
(nitrogen dioxide)Brown poisonous gasThe molecule has a odd number of electrons and in the gas phase. It exist in equilibrium with its colorless dimer N2O4NO2 dissolves in water to form nitric acid and nitrogen oxide which is leads to acid rain3NO2(g) + H2O(l)
2HNO
3
(aq) + NO(g)
NO
2
also initiates a complex sequence of smog forming photochemical reactions.
Slide28P-block Elements- V A elements
N
2
O (dinitrogen oxide)
Properties:TastelessUnreactiveNontoxic in small amountsSoluble in fatLike hydrogen azide, dinitrogen oxide can be pictured simply as a molecule that resonates between two electron-dot structures, one of which contains a NO bond and a NN bond and the other, a N O bond and a NN bond.Nitrogen Oxide and Oxoacids
Slide29P-block Elements- V A elements
Nitrogen Oxide and Oxoacids
Structure and Properties of Nitrogen Oxides
Slide30P-block Elements- V A elements
HNO
3
(Nitric acid)
HNO3 is used in the production of fertilizers and explosivesIt is both an acid and an oxidizing agentIt is made in the three-step Ostwald processSTEP 1: Oxidation of ammoniaNitrogen Oxide and Oxoacids(a) molecular structure of HNO3 (b) resonance structure
STEP 2: Oxidation of nitrogen oxide
2NO(g) + O
2
(g)
2NO
2
(g)
STEP 3: Disproportionation (single atom is both oxidized and reduced) in water;
3NO
2
(g) + H2O(l) 2HNO3(aq) + NO(g)4NH
3
(g) + 5O
2
(g)
850
o
C
,5
atm
,
Pt
/
Rh
→ 4NO(g) + 6H
2
O(g)
Slide31P-block Elements- V A elements
Phosphorus Oxides and Oxoacids
Oxoacids and
oxoanions
of phosphorous are among the most heavily manufactured chemicals.Phosphate fertilizer production consumes two-thirds of all the sulfuric acid produced in the US.The structures of the phosphorus oxides are based on the tetrahedral PO4 unit.Under acidic conditions, the highest oxidation state, +5, is the most stable species, as phosphoric acid, H3PO4, and under basic conditions, the phosphate ion, PO43-, is the most stableUsed primarily for the production of fertilizer, food additives, and detergent.Many soft drinks have a small amount of phosphoric acid.
Although the phosphorus in H
3
PO
4
has an oxidation number of +5, the acid shows a oxidizing power at temperatures above 350ºC
H
3
PO
4
(phosphoric acid
)
Slide32P-block Elements- V A elements
Phosphates (compounds contain PO
4
3-
)Phosphate rock is mined in huge quantities in Florida-USA and MoroccoThe rock is crushed and treated with sulfuric acid to give a mixture of sulfates and phosphates called superphosphates, a major fertilizerCa3(PO4)2(s) + 2H2SO4 (l) 2CaSO4 (s) + Ca(H
2
PO
4
)
2
(s)
Phosphorus Oxides and Oxoacids
Slide33P-block Elements- V A elements
http://chem.libretexts.org/Core/Inorganic_Chemistry/Descriptive_Chemistry/Elements_Organized_by_Block/2_p-Block_Elements/Group_15%3A_The_Nitrogen_Family/1Group_15%3A_General_Properties_and_Reactions