Difference Between Red and White Phosphorus

The key difference between red and white phosphorus is that the red phosphorus appears as dark red colored crystals whereas the white phosphorus exists as a translucent waxy solid that quickly becomes yellow when exposed to light.

Phosphorus is a chemical element that occurs in several different allotropes. The most common allotropes are red and white forms, and these are solid compounds. Furthermore, when exposed to light, the white form converts into the red form. However, there are several differences between these two allotropes. Let us discuss more details on the difference between red and white phosphorus.

CONTENTS

1. Overview and Key Difference
2. What is Red Phosphorus
3. What is White Phosphorus
4. Side by Side Comparison – Red vs White Phosphorus in Tabular Form
6. Summary

What is Red Phosphorus?

Red phosphorus is an allotrope of phosphorus that has a dark red color. It is the second most common allotrope of phosphorus. This compound is non-toxic and odorless. Moreover, it is chemically active. Unlike white phosphorus, it is not phosphorescent. In addition to that, this form is an amorphous network.

Further, this compound has a polymeric structure. It views as a derivative of P₄ units wherein one P-P bond is broken and one additional bond exists between two P₄ units. We can produce this compound via heat treating white phosphorous. That is, heating the white phosphorous up to 300 °C makes this conversion between two allotropic forms. However, we should do it in the absence of air. Or else, we can expose the white phosphorus to sunlight. This also forms the red allotrope. Moreover, it does not ignite in air at temperatures below 240 °C.

Applications:

• In matchboxes to produce fire
• As a component in flare products
• As a component in smoke devices
• To create methamphetamine
• Useful as a flame retardant

What is White Phosphorus?

White phosphorus is an allotrope of phosphorus which exists as a translucent waxy solid. This compound exists as molecules; as P₄ units. These molecules have a tetrahedral structure. This structure causes its ring strain and instability. There are two forms as alpha and beta form. The alpha form is the standard state.

This waxy solid quickly becomes yellow when exposed to sunlight. Therefore, sometimes we call it “yellow phosphorus”. It glows in a greenish appearance in the dark (in the presence of oxygen). Furthermore, it is toxic and highly flammable as well, and also has a self-igniting nature. We can store this compound underwater because it is slightly soluble in water. We can produce this allotrope using phosphate rocks; there we heat the rock in an electric or fuel-fired furnace (in the presence of carbon and silica). This evolves elemental phosphorus. We can collect this phosphorus under phosphoric acid. Moreover, this allotrope can self-ignite at around 50 °C.

Applications:

• As a weapon (due to the self-ignition at very low temperatures)
• As an additive in napalm
• To produce red phosphorus

What is the Difference Between Red and White Phosphorus?

Red phosphorus is an allotrope of phosphorus that has a dark red color. It exists as a polymeric network. Importantly, it appears as dark red colored crystals. Unlike white allotrope, it is nontoxic. Moreover, it ignites in air at temperatures above 240 °C. White phosphorus is an allotrope of phosphorus which exists as a translucent waxy solid. It exists as P4 molecules. This compound exists as a translucent waxy solid that quickly becomes yellow when exposed to light. It is highly toxic. In addition to that, it ignites in air at low temperatures such as 50 °C. The infographic below presents the difference between red and white phosphorus in tabular form.

Summary – Red vs White Phosphorus

There are two major allotropes of phosphorus as red and white phosphorus. The key difference between red and white phosphorus is that red phosphorus appears as dark red colored crystals whereas white phosphorus exists as a translucent waxy solid that quickly becomes yellow when exposed to light.

Reference:

1. Ray, Linda. “Sources of Red Phosphorus.” LIVESTRONG.COM, Leaf Group, 3 Oct. 2017. Available here  

Image Courtesy:

1.’Red phosphorus as powder’By Hi-Res Images ofChemical Elements (CC BY 3.0) via Commons Wikimedia
2.’White phosphorus, containing a small amount of red phosphorus’By Hi-Res Images ofChemical Elements – (CC BY 3.0) via Commons Wikimedia