Phosphorus is an important mineral that is essential for many functions in the human body. While pure phosphorus is colorless, the mineral phosphorus commonly occurs in nature in several colored forms. The color of phosphorus depends on factors like its allotrope, impurities present, and how it was processed.
Allotropes of Phosphorus
Phosphorus exists in several allotropic forms or allotropes, which refer to different structural modifications of an element. The principal allotropes of phosphorus include:
- White phosphorus
- Red phosphorus
- Black phosphorus
- Violet phosphorus
Each allotrope has different properties and a characteristic color. The color varies based on the molecular structure and level of impurities present.
White Phosphorus
White phosphorus is the most common allotrope, consisting of tetrahedral P4 molecules. It has a waxy white appearance when pure but can appear pale yellow with impurities.
Red Phosphorus
Red phosphorus has an amorphous polymeric structure made up of networks of P atoms linked with P-P bonds. It has a dark red color resembling brick red.
Black Phosphorus
Black phosphorus has a layered crystal structure of linked six-membered rings stacked together. It has a blackish-gray color with a metallic luster.
Violet Phosphorus
Violet phosphorus consists of an intermediate structure between red and black phosphorus. It has an imperfect layered structure and appears dark violet in color.
Common Phosphorus Minerals
Some naturally occurring phosphorus minerals also exhibit characteristic colors. Here are some of the common colored phosphorus mineral forms:
| Mineral | Color |
|---|---|
| Apatite | Usually greenish, yellow, brown or violet |
| Phosphosiderite | Brown, yellowish brown or golden brown |
| Vivianite | Deep blue |
| Lazulite | Deep blue |
| Wardite | Yellowish green or greenish yellow |
Factors Affecting Phosphorus Color
Several factors can influence the color that phosphorus takes in minerals and other compounds:
Allotropic Form
The specific allotrope of phosphorus present affects its color. For instance, red phosphorus lends a red color to compounds.
Impurities
Impurities present alongside phosphorus can alter its color. Iron, clay, and organic matter are common impurities.
Particle Size
The particle size of phosphorus affects the absorption and reflection of light, influencing its perceived color.
Processing Method
How phosphorus is processed and the conditions involved impact its final color. For example, white phosphorus slowly changes to red phosphorus when exposed to sunlight.
Oxidation State
The oxidation state of phosphorus can also affect its color. Higher oxidation states tend to be more vividly colored.
Coordination Environment
The atoms/ions surrounding phosphorus in a compound affect the absorption of light and observed color.
Common Colors of Phosphorus
Here is an overview of some of the common colors seen in phosphorus minerals and compounds:
White
White phosphorus has a waxy white appearance. It glows greenish-white in the dark due to chemiluminescence.
Red
Red phosphorus has a vivid red color resembling brick red. Red phosphorus powder is used in matches and flares.
Black
Black phosphorus is blackish-gray with a metallic sheen. It is the least reactive allotrope of phosphorus.
Yellow
Phosphorus can appear yellow when impure. Yellow phosphorus is toxic and volatile.
Green
Green colored phosphorus minerals like apatite owe their color to impurities present.
Blue
Some phosphorus minerals like lazulite and vivianite are deep blue in color.
Violet
Violet phosphorus is a transitional form between red and black phosphorus and has a dark violet hue.
Orange
Phosphorus orange is a reddish-orange colored solid used in safety matches. It is a mix of red phosphorus and mercury sulfide.
Brown
Phosphorus can take on a brownish tint when impure. Some minerals like phosphosiderite are brown colored.
Uses of Colored Phosphorus
The different colored allotropes and compounds of phosphorus have a number of uses:
- Red phosphorus is used in matches and flares.
- White phosphorus is used to make phosphoric acid and fertilizers.
- Violet phosphorus is used in solar cells.
- Black phosphorus is used as a semiconductor.
- Yellow phosphorus is used in pesticides and nerve agents.
- Phosphorus minerals like apatite are used as gemstones.
Conclusion
In summary, phosphorus can occur in a variety of colored forms depending on factors like allotrope, impurities, particle size, processing method and coordination environment. While pure phosphorus is colorless, common colors seen include white, red, black, yellow, green, blue, violet and brown. The different allotropes and colored compounds have diverse applications ranging from matches to pesticides and electronics.
