The elements in group 15Nitrogen

PhosphorusArsenic

AntimonyBismuth

Introduction• All are important elements• Increasing trend to metallic character and

cationic behavior from top to botom in the grroup

• Nitrogen is different with the other elements, even phosphorus

1. The diminished ability to form p-p π bond: radius, single bond

2. The possibility of utilizing the d orbitals: d-p π bond , CN

Introduction (continue)

• All , but Bi, are important donor atoms in their trivalent compounds

• Bismuth is a metal element, but sodium bismuthate is a very strong oxidizing agent: inert electron pair effect

Occurrence and Recovery of the Elements

Phosphorus

Principally obtained from phosphate rock-remains of fossilized life forms

Ca5(PO4)3F and Ca5(PO4)3OH

Ca5(PO4)3F(s) + H2SO4(I) 3H3PO4(l) + 5CaSO4(s) + HF(aq)

2Ca3(PO4)2 + 6SiO2 + 10C 6CaSiO3 + 10CO + P4

1500 °C

Elemental Phosphorus

White Phosphorus

Black Phosphorus

White Phosphorus:

• Reaction on previous slide• Ignites spontaneously in air

• Stored under water

Red Phosphorus:

•Heat white phosphorus at 300 C in inert atm for several days•Does not ignite in air•Structure: contain linear chain

Black Phosphorus•The most stable form

•Formed when P heated under high pressure.

Occurrence and Recovery of the Elements

Arsenic

Arsenic is found in nature in a number of minerals including

realgar (As4S4)

orpiment (As2S3)

arsenolite (As2O3)

iron minerals such as arsenopyrite (FeAsS) loallingite (FeAs2).

Arsenic is made on an industrial scale by heating appropriate minerals in the absence of air. The arsenic is condensed out as a solid.

FeAsS (700°C)      FeS + As(g) +   As(s)

Occurrence and Recovery of the Elements

Antimony

Antimony is found in nature in a number of minerals including

stibnite (Sb2S3)

ullmanite (NiSbS). Small amounts of native antimony have been found. Some ores are treatable under reducing conditions to form Sb2S3.

The sulphide is removed to leave elemental antimony with scrap iron.Sb2S3 + 3Fe      2Sb + 3FeSIn antehr process, some ores can be heated to evolve the oxide Sb2O3 and this in turn can be reduced by charcoal in

the presence of sodium sulphate, to ensure mixing, to form elemental antimony.

2Sb2O3 +3C      4Sb + 3CO2

Occurrence and Recovery of the Elements

Bismuth

Bismuth is found in nature largely as bismite (Bi2O3)

bismuthinite (Bi2S3)

bismutite [(BiO)2CO3].

However it is generally made as a byproduct of copper, lead,tin, silver, gold, and zinc plants. The final step involves a reduction of the oxide by charcoal.

Phosphine PH3

Typically prepared by the action of dilute acid on calcium or aluminum phosphide or by pyrolysis of H3PO3 or by reaction of KOH on white phosphorus

Pure phosphine is not spontaneously flammable but often inflames due to the presence of trace P2H4 or P4

•Readily oxidized by air once ignited•Sparingly soluble in water•Very weak base pKb 1E-25 PH4

+ is readily hydrolized

Extremely poisonous

Only phosphine of the lower Group 15 elements forms subhydrides - P2H4

Used as a semiconductor dopant source

Arsine AsH3

Even more poisonous than phosphine

Readily decomposes to yeild elemental arsenic-”arsenic mirror test”

Only know use as a semiconductor dopant source

Stibine SbH3 and Bismuthine BiH3

Limited stability makes these compounds of little interest•Bond energy (stability): NH3 >PH3 > AsH3 > SbH3 > BiH3

•Bond angle (HAH): NH3 >PH3 > AsH3 > SbH3 > BiH3

•Base strength in water: same as above•Reduce ability: NH3 <PH3 < AsH3 < SbH3 < BiH3

Compounds of Group 15 ElementsHalides: PX3 PX5

Phosphorus Fluorides

PF3

colourless gas •Melting point: -152°C •Boiling point: -102°C

P2F4

colourless gas •Melting point: -86.5 •Boiling point: -6.2

PF5

colourless gas •Melting point: -94°C •Boiling point: -85°C

2PCl3(l) + 3ZnF2(s) 2PF3(g) + 3ZnCl2(s)

Compounds of Group 15 Elements

Halides:

Arsenic Fluoridescolourless liquid

•Melting point: -6°C •Boiling point: 63°C

AsF3

“Bridged” structure, but essentially molecular

AsF5 colourless gas •Melting point: -79.8°C •Boiling point: -52.8°C

Compounds of Group 15 Elements

Other Halides

Colourless liquid •Melting point: -16°C •Boiling point: 130°C

AsCl3 Decomp at –50 °C Recall BrO4

–

AsCl5

white to pale yellow crystalline solid

Melting point: 31°C

Boiling point: 221°C

AsBr3

red crystalline solid •Melting point: 141°C •Boiling point: 400°C; 424°C

AsI3

Compounds of Group 15 Elements

Halides:

Antimony Fluorides

•colourless crystalline solid •Melting point: 290°C •Boiling point: 345°C

SbF3

SbF5 •viscous liquid •Melting point: 8.3°C •Boiling point: 141°C

Actual structure has intermolecular contacts giving highly distorted octahedral coordination

Forms tetrameric structure in the solid state

AsF3 and SbF3 are very useful as fluorinating agents

Compounds of Group 15 Elements

Other Halides

colourless or yellow liquid •Melting point: 4°C •Boiling point: 140°C •Why liquid when trichloride a solid?

SbCl5

red crystalline solid •Melting point: 170.5°C •Boiling point: 401°C

SbI3

SbBr3 white or yellow solid, deliquescent crystals •Melting point: 96°C •Boiling point: 288°C

white crystalline solid, deliquescent

•Melting point: 73.4°C •Boiling point: 223°C

SbCl3

Compounds of Group 15 Elements

Halides:

Bismuth Fluorides

grey-white crystalline solid •Melting point: 649°C •Boiling point: 900°C

BiF3

BiF5

white crystalline solid •Melting point: 154°C •Boiling point: 230°C

What do the m.p. and b.p. imply?

What do these m.p. and b.p imply?

Ionic lattice

Infinite linear BiF6 chains

Compounds of Group 15 Elements

Other Halides NonexistantBiCl5

green-black crystalline solid •Melting point: 408.6°C •Boiling point: 542°C

BiI3

BiBr3 •yellow, golden crystalline solid, deliquescent

•Melting point: 219°C •Boiling point: 462°C

•white or yellowish white crystalline solid,

•Melting point: 233.5°C •Boiling point: 441°C

BiCl3

Bismuth Bromide Structure

O2Cl3PO PCl3

RMgX, LiRPR3, PR2Cl, PRCl

AgNCOAgSCN

P(NCO)3 P(NCS)3H2O

HCl + H3PO3 + H4P2O5

N2O4

Cl3P=NPCl2O

RH + O2

RPOCl2 + HClRCl + AlCl3

[RPCl3]+[AlCl4]-

H2O

RPOCl2

NH3

P(NH2)3

Ni(CO)4

Ni(PCl3)4

ROHP(OR)3 in base(RO)2PHO in absence of base

RMgX

R3PO

ROH(RO)2PO

S

Cl3PS RCO2H

RCOCl+ H3PO3

Reactions of PCl3

Reactions ofother MX3

Halides similar

Oxides of P, As, Sb and Bi

P4O10 a good drying and detergent agent

P4 + 5O2 P4O10

Prepared by burning P in air

Limit the supply of oxygen and:

P4 + 3O2 P4O6

P4O10 + 6H2O 4H3PO4

P4O6 + 6H2O 4H3PO3

How to make an acid

Oxides of Arsenic, Antimony and Bismuth

Only As and Sb for (V) oxides, these are of limited stability.

As, Sb and Bi oxides primarily (III) oxidesAs2O3 Sb2O3 Bi2O3

Note: Acid-base property Oxide-reduce property

Gas Phase of As and Sb oxides:

Sulphide

• P4S3 P4S5 P4S7 P4S10… similar as oxides• Exclude P4S10, all contain at least one P–P

bond• As2S3 As2S5 As4S4 …• Sb2S3 Sb2S5

• Bi2S3 why ?• Note:1. Color: yellow to black. polarization covalent2. Solubility and oxidizing-reduce properties3. Reaction with H+, OH–, S2–, Sx

2–

Phosphorus Oxoanions:

Oxidation Number

Formula Name Structure Remarks

+1 H2PO2- Hypophosphit

eFacile

Reducing Agent

+3 HPO32- Phosphite Facile

Reducing Agent

+4 P2O64- Hypophosphat

eBasic

+5 PO43- Phosphate Strongly Basic

+5 P2O74- Diphosphate Basic

Chain variations

P

H

H OO

P

H

O OO

PO

OO

PO

OO

P

O

O OO

PO

OO

PO

OO

O

Structure and acidic strength of H3PO3

• Pauling rule:

1. HnROm: represented as ROm-n(OH)n

2. pK = 7 – 5(m – n)

3. In same type: electronegativity• Application:

1. H3PO3 P(OH)3 pK = 7

2. Experimental: pK = 2

3. H3PO3 HPO(OH)2

• P(OR)3

Poly- and cycle-phosphoric acid(pyrophasphoric acid)

• [PnO3n+1](n+2)–

Ex. Na5P3O10

• [PnO3n]n–

• Ex. Na5P3O9

• Note:

1. Solubilities of different phasphorates2. Reducing properties of Hypo-/phosphite

Phosphorus Nitrogen Compounds

The extra valence in N can make for some interesting structures - Phosphazenes

P

PP

P

N

NN

N

N N

R

R

RR

R

R

PCl5 + nNH4Cl (Cl2PN)n + 4nHCl

(Cl2PN)n + 2nCF3CF2O- [(CF3CF2O)2PN]n + 2nCl-

Substitutions by other Lewis bases are common

Polymeric structures common – rubber-like substances

-excellent low temperature properties

Hexachlorotriphosphazene

• planar• N sp2, P sp3 • d-p π • May form

polylimer

Complexes

• PF6– AsF6

– SbF6–

• NaSb(OH)6

• KH[Sb2(d-C4H2O6)2]

• Common for Bi3+

• Bi6O66+ Bi6O6(OH)3

3+

Bi6O6(OH)6