Chemistry of Nonmetals

1Dr.Riham Hazzaa

OXIDATION-REDUCTION REACTIONS

• A redox reaction involves the transfer of electrons between reactants

• Electrons gained by one species must equal electrons lost by another

• Both oxidation and reduction must occur simultaneously.

• Oxidation: removal of electrons • Reduction: gain of electrons

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• oxidising and reducing agents• An oxidizing agent is an element which causes

oxidation (and is reduced as a result) by removing electrons from another species. oxidizing agent is the electron acceptor

• A reducing agent is an element which causes reduction (and is oxidized as a result) by giving electrons to another species. reducing agent is the electron donor.

Na(s) + Cl (g) → NaCl(s)

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The main group metals are oxidized in all of their chemical reactions. These metals are oxidized when they react with nonmetal elements.

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• Nonmetals can undergo both oxidation and reduction.

• Phosphorus, is oxidized when it reacts with oxygen to form P4O10.

• it is reduced when it reacts with calcium to form calcium phosphide.

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• Phosphorus (EN = 2.19) is less electronegative than oxygen (EN = 3.44). When these elements react, the electrons are drawn toward the more electronegative oxygen atoms. Phosphorus is therefore oxidized in this reaction, and oxygen is reduced.

• Calcium (EN = 1.00), on the other hand, is significantly less electronegative than phosphorus (EN = 2.19). When these elements react, the electrons are drawn toward the more electronegative phosphorus atoms. As a result, calcium is oxidized and phosphorus is reduced.

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The behavior of the nonmetals• Nonmetals tend to oxidize metals.

• Nonmetals with relatively large electronegativities (such as oxygen and chlorine) oxidize substances with which they react.

• Nonmetals with relatively small electronegativities (such as carbon and hydrogen) can reduce other substances.

2 Mg(s)+O2(g)→2 MgO(s) 

2 H2S(g)+3 O2(g)→2 SO2(g)+2 H2O(g)

CuO(s)+ H2(g)→Cu(s)+H2O(g)

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Hydrogen• Compounds of hydrogen are frequently called

hydrides, even though the name hydride describes compounds that contain an H- ion.

H+=1s0

H=1s1

H-=1s2

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• Because hydrogen forms compounds with oxidation numbers of both +1 and -1, many periodic tables include this element in both Group IA (with Li, Na, K, Rb, Cs, and Fr) and Group VIIA (with F, Cl, Br, I).

• The first ionization energy of hydrogen (1312 kJ/mol), is halfway between the elements with the largest (2372 kJ/mol) and smallest (376 kJ/mol) ionization energies.

• Hydrogen has an electronegativity (EN = 2.20) halfway between the extremes of the most electronegative (EN = 3.98) and least electronegative (EN = 0.7) elements. 9

Dr.Riham Hazzaa

• Hydrogen is oxidized by elements that are more electronegative to form compounds in which it has an oxidation number of +1.

• Hydrogen is reduced by elements that are less electronegative to form compounds in which its oxidation number is -1.

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Formation of Hydrogen• By reacting an active metal with water.

• By reacting a less active metal with a strong acid.

2 Na(s)+2 H2O(l)2 Na+(aq)+2 OH-(aq)+H2(g)↑

Zn(s) +2 HCl(aq)Zn2+(aq)+2 Cl-(aq)+ H2(g)↑

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• By reacting an ionic metal hydride with water

• By decomposing water into its elements with an electric current.

NaH(s)+H2O(l)Na+(aq)+OH-(aq)+H2(g)

 electrolysis     

2 H2O(l) 2 H2(g)+O2(g) 

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The Chemistry of Nitrogen (GroupV)

• A neutral nitrogen atom contains five valence electrons: 2s2 2p3.

• Because the covalent radius of a nitrogen atom is relatively small (only 0.070 nm), nitrogen atoms come close enough together to form very strong bonds.

• The strength of the nitrogen-nitrogen triple bond makes the N2 molecule very unreactive.

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The Synthesis of Ammonia NH3 Haber process

• The Haber process, a mixture of N2 and H2 gas at 200 to 300 atm and 400 to 600oC is passed over a catalyst of finely divided iron metal.

• Two-thirds of the ammonia used for fertilizers is converted into solids such as ammonium nitrate, NH4NO3; ammonium phosphate, (NH4)3PO4; ammonium sulfate, (NH4)2SO4; and urea, H2NCONH2. The other third is applied directly to the soil as anhydrous ammonia.

   Fe  

N2(g)+3 H2(g)2 NH3(g)  

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• The Synthesis of Nitric Acid Ostwald process

4 NH3(g)+5 O2(g)4 NO(g)+6 H2O(g)

2 NO(g)+O2(g)2 NO2(g)   

3 NO2(g)+ H2O(l)2 HNO3(aq)+NO(g)

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The Nitrogen Oxides 1. Dinitrogen oxide, N2O which is also known as

nitrous oxide, can be prepared by carefully decomposing ammonium nitrate.

 170 to 200oC    

NH4NO3(s)N2O(g)+2 H2O(g)

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2. Nitrogen oxide, or nitric oxide,

Nitrogen oxide NO can be prepared in the laboratory by reacting copper metal with dilute nitric acid.

N2(g) +O2(g)2 NO(g)

3 Cu(s)+8 HNO3(aq) 3 Cu(NO3)2(aq)+2 NO(g)+4 H2O(l)

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3. Nitrogen dioxide NO2

NO reacts rapidly with O2 to form nitrogen dioxide (once known as nitrogen peroxide), which is a dark brown gas at room temperature.

It can also be made by reacting copper metal with

concentrated nitric acid,

2 NO(g)+O2(g)2 NO2(g)

Cu(s)+4 HNO3(aq)Cu(NO3)2(aq)+2 NO2(g)+2 H2O(l)

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4. Dinitrogen pentoxide By carefully removing water from concentrated

nitric acid at low temperatures with a dehydrating agent we can form dinitrogen pentoxide.

4 HNO3(aq)+P4O10(s)2 N2O5(s) +4 HPO3(s)

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