Is Phosphorus a Solid, Liquid or Gas? (+ 3 Things to Know)

Phosphorus is a solid element at room temperature and standard pressure. ¹ Its melting point is 44.15 °C (111.47 °F), and its boiling point is 280 °C (536 °F). At room temperature, phosphorus exists in several allotropic forms, including white, red, and black phosphorus, each with distinct properties. ^{2 3}

Well, this was just a simple answer. But there are few more things to know about this topic which will make your concept super clear.

So let’s dive right into it.

Why does phosphorus exist as a solid at room temperature?

Phosphorus exists as a solid at room temperature because of its relatively high melting point and the intermolecular forces that hold its atoms together in a solid crystal lattice.

The melting point of elemental phosphorus is around 44 °C, which is relatively high compared to other non-metallic elements. ⁴ At room temperature (around 25 °C), phosphorus is therefore in its solid state. This is why phosphorus appears as a soft, waxy, and somewhat brittle substance, which can be easily cut or molded.

The solid state of phosphorus is due to the strong covalent bonds that exist between the phosphorus atoms, which form a crystal lattice structure. In this structure, each phosphorus atom is covalently bonded to three other phosphorus atoms, creating a tetrahedral arrangement. ⁵

The resulting lattice is held together by weak van der Waals forces, which are relatively strong for a non-metallic element and contribute to the solid nature of the substance.

Overall, the combination of a high melting point and strong intermolecular forces make phosphorus a solid at room temperature.

Does phosphorus exist in a liquid state?

Yes, elemental phosphorus can exist in a liquid state, although it is not commonly encountered in this state under normal conditions.

The melting point of white phosphorus, the most common form of elemental phosphorus, is around 44 °C, and its boiling point is around 280 °C. Therefore, if white phosphorus is heated above its melting point, it will become a liquid. However, this is not typically done as white phosphorus is highly reactive and can ignite spontaneously in air.

Red phosphorus, another allotrope of phosphorus, has a higher melting point of around 590 °C and does not ignite spontaneously in air. ⁶ Therefore, it can be melted and is used in various industrial applications such as in the production of matches and flame retardants.

In summary, while elemental phosphorus can exist in a liquid state, it is not commonly encountered due to its high reactivity and tendency to ignite spontaneously in air.

How is solid phosphorus different from liquid phosphorus?

Solid phosphorus and liquid phosphorus are different states of matter with distinct properties.

Solid phosphorus

Solid phosphorus exists as a soft, waxy, and somewhat brittle substance, which can be easily cut or molded. ⁷ It is typically a white or yellowish color and is transparent to light. Solid phosphorus is relatively stable under normal conditions but is highly reactive and can ignite spontaneously in air. ⁸

Liquid phosphorus

Liquid phosphorus, on the other hand, is a clear or yellowish liquid with a density of around 1.8 g/cm³. ⁹ It is less viscous than molasses but more viscous than water. Liquid phosphorus has a relatively low boiling point of around 280 °C, and it can ignite spontaneously in air.

The chemical properties of solid and liquid phosphorus are also different. Solid phosphorus is typically more reactive than liquid phosphorus due to the presence of unstable P4 molecules in the solid state. In contrast, liquid phosphorus is less reactive because the P4 molecules are broken down into more stable P2 molecules. ¹⁰

Overall, while solid and liquid phosphorus share some similar properties, such as their toxicity and their ability to ignite spontaneously in air, they are different states of matter with distinct physical and chemical properties.

Further reading

Is Sodium a Solid, Liquid or Gas?
Is Oxygen Solid, Liquid or Gas?
Is Lithium Solid, Liquid or Gas?
Is Magnesium a Solid, Liquid or Gas?
Is Nitrogen a Solid, Liquid or Gas?

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