Phosphorus Definition
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.
[Image will be Uploaded Soon]
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.
[Image will be Uploaded Soon]
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
1. What are the main allotropes of phosphorus and what are their key properties?
Phosphorus primarily exists in three allotropic forms: white, red, and black phosphorus. Each has distinct properties:
- White Phosphorus: A translucent, waxy solid with a discrete tetrahedral P₄ structure. It is highly reactive due to angular strain, poisonous, insoluble in water, and glows in the dark (chemiluminescence). It must be stored under water to prevent spontaneous ignition in air.
- Red Phosphorus: Formed by heating white phosphorus in an inert atmosphere. It has a polymeric structure, making it much more stable, less reactive, and non-poisonous. It does not glow in the dark and is used in the striking surface of matchboxes.
- Black Phosphorus: The most stable allotrope, formed by heating white phosphorus under high pressure. It has a layered structure similar to graphite, is a semiconductor, and is the least reactive of the three.
2. What are the major industrial and biological uses of phosphorus?
Phosphorus and its compounds have crucial applications in both industry and biology.
- Industrial Uses: The primary use is in the production of fertilisers like superphosphate of lime. It is also used in making safety matches, pyrotechnics, smoke bombs, and certain alloys like phosphor bronze. Phosphorus compounds are also used as water softeners and in food preservation.
- Biological Uses: Phosphorus is essential for life. It is a key component of DNA and RNA (forming the sugar-phosphate backbone), ATP (the energy currency of cells), and phospholipids (which make up cell membranes). It is also vital for the formation of strong bones and teeth as part of calcium phosphate.
3. How does phosphorus typically react with halogens and alkalis?
The reactivity of phosphorus allows it to form a variety of compounds with halogens and alkalis.
- Reaction with Halogens: Phosphorus reacts with halogens (like chlorine) to form two types of halides. In a limited supply of the halogen, it forms a trihalide (e.g., PCl₃). In an excess of the halogen, it forms a pentahalide (e.g., PCl₅). The reaction is: P₄ + 6Cl₂ → 4PCl₃ (limited); P₄ + 10Cl₂ → 4PCl₅ (excess).
- Reaction with Alkalis: White phosphorus reacts with a hot, concentrated solution of an alkali like sodium hydroxide (NaOH) to produce phosphine gas (PH₃) and sodium hypophosphite (NaH₂PO₂). This is a classic example of a disproportionation reaction, where phosphorus is both oxidised and reduced.
4. Why is white phosphorus highly reactive and stored under water, while red phosphorus is relatively stable?
The difference in reactivity is due to their molecular structures. White phosphorus exists as discrete P₄ tetrahedral molecules. The P-P-P bond angle in this structure is only 60°, which is a significant deviation from the ideal tetrahedral angle. This creates high angular strain, making the bonds weak and the molecule very unstable and reactive. To prevent it from spontaneously reacting with oxygen in the air, it is stored under water. In contrast, red phosphorus has a more stable polymeric structure, consisting of a network of interlinked P₄ tetrahedra. This structure relieves the angular strain, making it much less reactive and more stable at room temperature.
5. How does the chemical behaviour of phosphorus differ from nitrogen, despite being in the same group?
Although both are in Group 15, phosphorus and nitrogen exhibit significant differences in their chemical behaviour for several key reasons:
- Expanded Octet: Phosphorus is in the third period and has vacant d-orbitals in its valence shell. This allows it to expand its octet and form compounds like PCl₅ and PF₆⁻. Nitrogen, in the second period, lacks d-orbitals and cannot form more than four covalent bonds.
- Multiple Bonding: Nitrogen forms very stable triple bonds (pπ-pπ bonding) with itself, resulting in the diatomic N₂ molecule. Phosphorus atoms are larger, and their p-orbitals are more diffuse, leading to weaker pπ-pπ overlap. Thus, phosphorus prefers to form single bonds and exists as P₄, not P₂.
- Catenation: Phosphorus shows a greater tendency for catenation (forming chains and rings of P-P single bonds) than nitrogen, whose N-N single bond is relatively weak.
6. Why can phosphorus form compounds like PCl₅, exhibiting an expanded octet, whereas nitrogen cannot?
The ability of phosphorus to form PCl₅ is directly related to its electronic configuration and position in the periodic table. Phosphorus (atomic number 15) is in the third period, and its valence shell configuration is 3s²3p³. It also has vacant, low-energy 3d orbitals. During bond formation, one of the 3s electrons can be promoted to a 3d orbital, resulting in five unpaired electrons. These five orbitals (one 3s, three 3p, and one 3d) can hybridise to form five equivalent sp³d hybrid orbitals, which then form five single bonds with chlorine atoms. Nitrogen, being in the second period, has its valence electrons in the n=2 shell, which contains only s and p orbitals (2s²2p³). It has no d-orbitals in its valence shell, so it cannot promote an electron to create more than three unpaired electrons or accommodate more than eight electrons in its valence shell.
7. What are oxoacids of phosphorus, and can you give two important examples?
Oxoacids of phosphorus are acids that contain phosphorus, oxygen, and at least one hydrogen atom bonded directly to an oxygen atom, which can be released as an H⁺ ion. A key feature of these acids is that phosphorus is tetrahedrally surrounded by other atoms. Two important examples are:
- Phosphorous Acid (H₃PO₃): Despite its formula, it is a dibasic acid. This is because only two hydrogen atoms are attached to oxygen atoms; the third is directly bonded to the phosphorus atom (P-H bond) and is not ionisable.
- Phosphoric Acid (H₃PO₄): This is a tribasic acid because all three hydrogen atoms are attached to oxygen atoms (P-OH bonds) and can be ionised. It is one of the most important phosphorus compounds, widely used in fertilisers, detergents, and as a food additive.
