Properties of Group 15 Elements

Periodic Trends

All Group 15 Elements tend to follow the general periodic trends:

• Electronegativity (the atom's ability of attracting electrons) increases up the group.
• Ionization Energy (the amount of energy required to remove an electrom from the atom in it's gaseous phase) increases up the group.
• Atomic Radii (the radius of the atom) increases down the group. 
• Electron Affinity (ability of the atom to accept an electron) increasese going up the group.
• Melting Point (amount of energy required to break bonds to change a solid phase substance to a liquid phase) increases going down the group.
• Boiling Point (amount of energy required to break bonds to change a liquid phase substance to a gas) increases going down the group. 
• Metallic Character (how metallic the atom is) increases going down the group. 

Nitrogen

Nitrogen was discovered in 1770 by Scheele and Priestley. This non-metallic element has no color, taste or odor and is present in nature as a noncombustible gas. When compared with the rest of Group 15, Nitrogen has the highest electronegativity which illustrates it is the most nonmetallic of the group. The common oxidation states of Nitrogen are +5, +3 and -3. Nitrogen makes up about 0.002% of the Earth's crust, however it constitutes 78% of the volume in Earth’s atmosphere.  Nitrogen has also been discovered in the atmosphere's of Venus and Mars. Venus has a 3.5% Nitrogen volume in its atmosphere and Mars contains 2.7% Nitrogen volume in its atmosphere.  Natural sources of nitrogen can be found in animal/plant proteins and in fossilized remains of ancient plant life. Important nitrogen-containing minerals are niter, KNO₃ and soda niter NaNO₃ which are found in desert regions and are important in fertilizers. Before the process of converting Nitrogen into Ammonia was discovered, sources of Nitrogen were limited. One of the processes of converting Nitrogen to Ammonia is the Haber-Bosch process. This process is therefore very important for the production of nitrogen. Nitrogen has very little solubility in liquids. N₂ does not have any allotropes. The unusually stable N₂(g) nitrogen gas is the source in which all nitrogen compounds are ultimately derived. N₂(g) is stable due to its electronic structure, the bond between the two Nitrogen atoms of N₂ is a triple covalent bond which is strong and hard to break. The enthalpy change associated with breaking the bonds in N₂ is highly endothermic N₂(g) -> 2N(g) ΔH = +945.4 kJ. Nitrogen gas is used as a refrigerant, metal treatment, and pressurized gas for oil recovery. Aditionally, the Gibbs energy of Nitrogen compounds are also not spontaneous and do not occur at normal temperatures. 1/2N₂(g) + 1/2O_{2 ->} NO(g)  ΔG_f= +86.55kJ. The oxides and oxyacids of nitrogen are nitrous oxide (N₂O), nitrogen oxide (NO), and nitrogen dioxide (NO₂).  Nitrous oxide is “laughing gas” used in dental work, child birth and to increase the speed of cars.  Nitrogen oxide is found in smog and neurotransmitters. Hydrazine, N₂H₄ is a poisonous, colorless liquid that likes to explode in air; it is a good reducing agent, therefore, methyl hydrazine is used as a rocket fuel. 

Phosphorus

Phosphorus is a nonmetallic element. The most common oxidation state of Phosphorus is -3. Phosphorus is the eleventh most abundant element, which makes up .11% of the Earth's crust.  The main source of phosphorus compounds come from phosphorus rocks. Phosphorous is not found purely in nature, but found in the form of apatite ores. Apatitie ores are compounds such as Fluorapatite Ca₅(PO₄)₃F which is in fluoridated water that can be used to strenghthen teeth and Hydroxylapatite, Ca₁₀(OH)₂(PO4)₆ which is a major component of tooth enamel and bone material. Phosphorus exhibits allotropic forms, the most common forms at room temperature are white phosphorus and red phosphorus.  White phosphorus is a white, waxy solid that can be cut with a knife.  The basic structure is a tetrahedral, P₄. White phosphorus is toxic, while red phosphorus is nontoxic.  Red phosphorous forms when white phosphorous is heated to 573 Kelvin and not exposed to air. Red phosphorus is less reactive than white phosphorus. Red phosphorus has a chain like polymeric structure, and is a more stable form.  Both white and red forms are incendiary and have been used to make match tips, although use of the white has been largely discontinued due to toxicity. Phosphorus has many uses, for example Phosphorus trichloride PCl₃ makes soaps, detergents, plastics, synthetic rubber nylon, motor oils, insecticides and herbicides. Phosphate as a polyprotic acid, H₃PO₄ can be used to make fertilizers; Phosphorus is an essential nutrient for plant growth but heavy fertilizer may lead to phosphate pollution in lakes, ponds and streams. Phosphorus also has many uses in the food industry, it can be used to make baking powders, instant cereals, cheese, the curing of ham, and it is in soft drinks to impart the tartness. 

Arsenic

Arsenic is a highely poisonous metalloid. Since it is a metalloid Arsenic has a high density, moderate thermal conductivity, and limited ability to conduct electricity. The oxidation states of Arsenic are +5, +3, +2, +1 and -3. The three allotropic forms are Arsenic are yellow, black and gray, with gray being the most common. Compounds of Arsenic are used in insecticides, weed killers, and alloys. The oxide of Arsenic is amphoteric which means it can act as both an acid and a base. Arsenic is mainly obtained by the heating of arsenic containing sulfides. The chemical formula for this process is FeAsS(s) -> FeS(s) + As(g). The As(g) deposits as As(s) which can then further be used to make other compounds. Arsenic can also be obtained by the reduction of Arsenic(III) Oxide with CO(g).  

Antimony

Antimony is also a metalloid. The oxidation states of Antimony are +3, -3, and +5. Atimony exhibits allotropy with the most stable being the metallic form which has the same properies as Arsenic of high density, moderate thermal conductivity and limited ability to conduct electricity. The oxide of Antimony is Antimony (III) oxide which is amphoteric, meaning it can act as both an acid and base. Antimony is obtained mainly from its sulfide ores. At low temperatures, Antimony vaporizes. Along with Arsenic, Antimony is commonly used in making alloys of other metals. Arsenic, Antimony and Lead will produce an alloy that has desirable properties for electrodes to use in lead-acid batteries. Arsenic and antimony are also used to produce semiconductor materials such as GaAs, GaSb, and InSb in electronic devices. 

Bismuth

Bismuth is a metallic element. The oxidation states of Bismuth are +3 and +5. Bismuth is a poor metal that is similar to both Arsenic and Antimony. Bismuth is commonly used in cosmetic products and medicine. Out of the group, Bismuth has the lowest electronegativeity and ionization energy which means that it is more likely to lose an electron than the rest of the Group 15 elements. This is why Bismuth is the most metallic of Group 15. Bismuth is also a poor electrical conductor. The oxide of Bismuth is Bismuth(III) Oxide which acts as a base, an expected property of metal oxides. Bismuth is obtained as a by-pruduct from the refining of other metals which allows other metals to recycle their by-products into Bismuth. 

Outside Links

• Wikipedia Article on the Haber-Bosch process for converting nitrogen to ammonia: http://en.wikipedia.org/wiki/Haber-Bosch_Process
• Youtube clip on the chemical and physical properties of White Phosphorus: http://www.youtube.com/watch?v=Oke8GinWDG8
• Coppola, Brian D.; Hovick, James W.; Daniels, Douglas S. "I Scream, You Scream...: A New Twist on the Liquid Nitrogen Demonstrations." J. Chem. Educ.1994, 71, 1080.
• Youtube clip-Elementary Productions: Solid Nitrogen: http://www.youtube.com/watch?v=mBAIiXow0GE

References

1. Petrucci, Ralph H., William S. Harwood, Geoff E. Herring, and Jeffry D. Madura. General Chemistry : Principles and Modern Applications. Upper Saddle River: Prentice Hall PTR, 2006.
2. Kotz, John C., and Paul Treichel. Chemistry and Chemical Reactivity. 3rd ed. New York, CA: Saunders College, 1996.
3. Häussinger, Peter, Paul Leitgeb, and Bernd Schmücker. "Nitrogen."  Nitrogen (2000): 1-25. Ullmann's Encyclopedia Of Industrial Chemistry. Web. 21 May 2010. <https://vpn.lib.ucdavis.edu/emrw/978....wiley.com+htm> 

Problems

1. How much of the Earth's crust is made up of Nitrogen?
2. How much of Earth's curst is not made up of Phosphorus? 
3. What kind of bond does N₂ have?
4. How are Red Phosphorus and White Phosphorus related to each other?
5. What is the electron configuration of Arsenic?
6. Does Bismuth have metallic properties or nonmetallic properties? 
7. True or False: Nitrogen and Phosphorus are metals.
8. Which Group 15 element has a greatest atomic radius? 
9. Which Group 15 element is the strongest reducing agent?
10. True or False: Bismuth exhibits the most metallic character.
11. What is the most common physical form of Nitrogen?
12. What is the process in which Nitrogen can convert into Ammonia?
13. Which element has the highest first ionization energy?
14. Complete and balance the following reaction: _N₂(g) + _H₂(g) -> ____
15. What is the common oxidation state of all Group 15 elements?

Answers

1. 0.002% of Earth's crust is made of Nitrogen.
2. Earth's crust is made up of .11% of Phosphorus so 99.89% of Earth's crust is not made up of Phosphorus.
3. N₂ has a triple covalent bond that is strong and hard to break.
4. Red Phosphorus and White Phosphorus are both allotropes of Phosphorus. Red phosphorus comes from White Phosphorus when it is heated to about 573 Kelvin.
5. [Ar] 3d¹⁰ 4s² 4p³
6. Bismuth has metallic properties.
7. True, both Nitrogen and Phosphorus are metals.
8. According to periodic trends, Bismuth has the greatest atomic radius.
9. According to periodic trends, Bismuth is the strongest reducing agent since it has an electronegativity value of 1.9 which is the same as Antimony but it has a lower ionization energy of 703 kJ/mol which means it is more likely to get oxidized.
10. True, Bismuth is the only metallic element of Group 15.
11. The most common physical form of Nitrogen is a colorless gas.
12. The process of converting Nitrogen into Ammonia is known as the Haber-Bosch process.
13. According to periodic trends, Nitrogen would have the highest first ionization energy which means that it does not want to lose an electron the most.
14. N₂(g) + 3H₂(g) -> 2NH₃(g)
15. The common oxidation state for all Group 15 elements is -3. 

Contributors

• Kirenjot Grewal (UCD), Connie Sou (UCD)

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