Physical and Chemical Properties of Phosphorus with Key Reactions and Examples
Phosphorus hailing from the family of nitrogen is a non-metallic chemical. This chemical is pale, transparent, semi-transparent, odourless, and tasteless in nature. It is not available freely in nature in any form. Being the 15th element in the periodic table, phosphorus emits flumes when put in contact with air. It is stored in water in most chemical laboratories to avoid catching fumes or fire.
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The occurrence of phosphorus in the crust of the earth is about 0.12% and occurs as phosphate. The United States, the largest producer of phosphorus, mined 13,300,000 metric tons in the year 1996. Bone ash and urine were the first primary sources of phosphorus.
Symbol: P
Formula: P2
Atomic Number: 15
Atomic Mass: 30.973762 u (the number of protons and neutrons present in an atom)
Forms: White & red phosphorous
Discovery of Phosphorus
The discovery of phosphorus dates back to 1669 by Hennig Brand. Strongly believing that urine had the capacity to transform lead into gold paved the way to the discovery of this non-metallic chemical. Further, he started heating and purifying about 60 buckets of urine just to find out the magical element that could turn into gold. It was exactly then he discovered ‘Phosphorus’.
Properties
There are three allotropic forms of phosphorus – they are pale or white phosphorus, red and black phosphorus. The phosphorus chemical element properties and reactions vary as per these forms.
White Phosphorous – It is waxy and transparent in nature. The boiling point of phosphorus is 240 degrees Celsius and the melting point being at 44 degrees celsius. It is used in building devices that lit the fire.
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Red Phosphorus – Red phosphorus is commonly seen on one side of the matchstick. The red phosphorus is formed as a result of heating white phosphorus at 250 degrees celsius. It does not dissolve in liquids.
Black Phosphorous – The black one is obtained by heating white phosphorus in really high pressure.
Black Phosphorous – The black one is obtained by heating white phosphorus in really high pressure. It resembles graphite.
Phosphorus is classified into group 15 of the periodic table. It is solid as per the physical state.
Medical Uses of Phosphorus
Phosphorus-32 is the radioactive isotope. Its uses are varied. It is used in various medical treatments such as the polycythaemia vera. It helps detect tumours in various parts of the body, such as the brain, breasts, etc. The radiations of radioactive isotope phosphorus-32 treat cancer.
Reactions
The shell arrangement of phosphorus is like the arrangement of nitrogen. The 3 half orbits form a single covalent bond. When combined with various elements, phosphorus shows oxidation. Phosphorus is said to have larger atoms and low electronegativity which influences its properties and reactions. Unlike nitrogen, phosphorus allows the expansion of octet, which leads to the formation of 5 covalent bonds in compounds.
Biological Aspects of Phosphorous
Phosphorus is found as phosphate in the body. Phosphate is found in the DNA and RNA of the human body. Phosphorus is an active part of the distribution of energy throughout the human body.
The recommended dietary intake of phosphate is 800 mg per day. Some of the foods that are rich in phosphorus are turkey, chicken, tuna, eggs, salmon, cheese etc. Consumption of phosphate in larger quantities than that which is required leads to serious health issues like osteoporosis, kidney problems etc. Exposure to white phosphorus sometimes leads to drowsiness, nausea, stomach pain etc., in some people.
Applications of Phosphorus in Industrial Use
Phosphorus is utilized in the production of steel, in the manufacture of fertilisers, improving the quality of the crop or soil. It can yield phosphine and phosphorus oxyacids which are used in commercial pest control. They are used as smoke screens, incendiary fire or bombs in the field of the military. Other industrial uses of phosphorus are –
Flame retardant
Aid in processing
Metal alloy constituent
Intermediates
agricultural chemicals
Material recovery
Plastic production
Fabricated metal product manufacturing
Resin manufacture
Organic chemical manufacture etc.
Variable Oxidation State
The variable oxidation state of phosphorus goes from -3 to +5.
Sample Questions and Answers
1. What are the Properties and Uses of Red Phosphorus?
Ans: Red phosphorus is derived by heating the white phosphorus. It is stable when compared to white phosphorus. Its melting point is at 860K.
There are many uses of red phosphorus – used in matchsticks, production of pesticides, organic synthesis, production of smoke bombs, water softening, electroluminescent coating, etc.
2. Who Discovered Red Phosphorus?
Ans: Red phosphorus was discovered by an Australian chemist named Anton von Schrotter. He discovered it in the process of heating white phosphorus at 482 degrees celsius in the presence of nitrogen.
3. Is Phosphorus Present in the Human Body?
Ans: Yes, phosphorus is present in the human body. It is found in the liver, kidney tissues, brain, blood, saliva, urine.
FAQs on Properties and Reactions of Phosphorus Explained for Chemistry Students
1. What are the physical properties of phosphorus?
The physical properties of phosphorus depend on its allotrope, with white, red, and black phosphorus showing different colors, densities, and melting points.
- White phosphorus (P4): soft, waxy, pale yellow, low melting point (~44°C), glows in air, highly toxic.
- Red phosphorus: dark red powder, more stable, higher melting point, non-luminous, less toxic.
- Black phosphorus: shiny, layered structure, highest density, good electrical conductivity.
2. What are the chemical properties of phosphorus?
The chemical properties of phosphorus include its ability to react with oxygen, halogens, metals, and alkalis to form oxides, halides, phosphides, and phosphine.
- With oxygen: P4(s) + 5O2(g) → P4O10(s)
- With chlorine: P4(s) + 6Cl2(g) → 4PCl3(l)
- With metals (e.g., sodium): 3Na(s) + P(s) → Na3P(s)
- With alkali: P4(s) + 3OH-(aq) + 3H2O(l) → PH3(g) + 3H2PO2-(aq)
3. What are the allotropes of phosphorus?
The main allotropes of phosphorus are white, red, and black phosphorus, which differ in structure and reactivity.
- White phosphorus: tetrahedral P4 molecules, very reactive and toxic.
- Red phosphorus: polymeric structure, more stable and less reactive.
- Black phosphorus: layered structure similar to graphite, most stable form.
4. Why is white phosphorus more reactive than red phosphorus?
White phosphorus is more reactive than red phosphorus because it contains strained P4 tetrahedral molecules with bond angles of 60°, which are highly unstable.
- The small bond angle creates angle strain.
- It reacts readily with oxygen, even at room temperature.
- Red phosphorus has a polymeric structure with less strain and greater stability.
5. How does phosphorus react with oxygen?
Phosphorus reacts with oxygen to form phosphorus oxides, mainly P4O10 in excess oxygen.
- In excess oxygen: P4(s) + 5O2(g) → P4O10(s)
- In limited oxygen: P4(s) + 3O2(g) → P4O6(s)
6. How does phosphorus react with chlorine?
Phosphorus reacts with chlorine to form phosphorus trichloride or phosphorus pentachloride depending on chlorine supply.
- Limited chlorine: P4(s) + 6Cl2(g) → 4PCl3(l)
- Excess chlorine: P4(s) + 10Cl2(g) → 4PCl5(s)
7. What is the oxidation state of phosphorus in its compounds?
The common oxidation states of phosphorus are −3, +3, and +5.
- −3 in phosphides and phosphine (e.g., PH3).
- +3 in phosphorus trichloride (PCl3).
- +5 in phosphoric acid (H3PO4) and phosphorus pentoxide (P4O10).
8. How is phosphine (PH3) prepared from phosphorus?
Phosphine is prepared by heating white phosphorus with sodium hydroxide solution, producing PH3 and sodium hypophosphite. The balanced reaction is:
- P4(s) + 3OH-(aq) + 3H2O(l) → PH3(g) + 3H2PO2-(aq)
9. What are the uses of phosphorus and its compounds?
Phosphorus and its compounds are widely used in fertilizers, matches, detergents, and industrial chemicals.
- Phosphates in fertilizers (e.g., superphosphate).
- Red phosphorus in safety matches.
- Phosphoric acid (H3PO4) in food and beverages.
- PCl3 and PCl5 in chemical synthesis.
10. What is the difference between white, red, and black phosphorus?
The difference between white, red, and black phosphorus lies in their structure, stability, and reactivity.
- White phosphorus: P4 molecules, very reactive, toxic, low melting point.
- Red phosphorus: polymeric chains, moderately reactive, safer to handle.
- Black phosphorus: layered crystalline structure, most stable and least reactive.
