Metal Vapours Are All Around Us
It all started on an uncomfortably warm Wednesday afternoon with an OCR A Level Chemistry textbook and a single question: can metals be vapours? Short answer, yes. A key characteristic of metallic bonding is its extremely high melting points and boiling points (apart from Mercury, which is liquid at room temperature), but metals still have boiling points. It’s not that simple. Perhaps a better question to ask would be can metals remain in a gaseous state? And if so, in what conditions? We can answer these questions in a few different ways.
It is widely known, metals, like all other pure substances, have melting points and boiling points, of which are extremely high, with the highest melting point being Tungsten’s at around 3422 ºC. The amount of energy required to break these metallic bonds through heating depends on the strength of the electrostatic forces. To transition from solid to liquid state, the temperature of the metal increases gradually before coming to a stop at its melting point. In this time where the temperature stops increasing, internal energy within the metal increases, breaking the bonds in the substance to form a liquid state. This process takes longer for metals with stronger electrostatic forces as more energy is required to overcome them. To transition from a liquid to a gaseous state, the metal would have to reach extreme temperatures and sustain its boiling point to allow the internal energy to increase and fully break the electrostatic forces between atoms and achieve gaseous metals.
You may not believe it but, metal vapours are used in many industries. One key example of this is in sodium-vapour lamps, often used in street-lights. Inside the lamp, a current is applied through an electrode in one end of the filament. The energy supplied from this initiates a low pressure arc that takes place in an inert gas mixture (typically neon and argon). The mixture gradually heats up the sodium into its excited state, combatting its inability to sustain the gaseous state for long periods of time naturally, and preventing further reaction from occurring. In low pressure sodium lamps, this produces a yellow-orange colour that releases little heat, making it more energy efficient, however the colour can be changed by converting this lamp to a high pressure one, which commonly has a brighter and whiter light. This is achieved by increasing the internal pressure of the lamp and often including other metals such as mercury. One disadvantage of a high pressure lamp is that it releases more heat than a low pressure sodium lamp, making it less efficient. The monochromatic light seen in low pressure sodium lamps restricts its use to outdoor areas, like in streetlights, whereas the brighter light seen in high pressure lamps makes it more common in industrial and sports lighting. Unfortunately, these fascinating lamps are gradually being replaced with LEDs in the UK, leaving the signature yellow glow of streetlights as a memory of the past. On the bright side, the exemption of the use of mercury in high pressure sodium lamps has been extended to 24th February 2027, so keep an eye out, because if you’re lucky, you might just find one.
To conclude, while pure metals can reach a gaseous state at extremely high temperatures, it is very unlikely that they should stay in this state without reacting with other substances. A common condition required to keep metals as vapours is the presence of the noble gases, as explained in the workings of sodium vapour lamps. So, although it may not be as easy as bringing metal to flame, metal vapours do exist, and they’re all around us.
- Ruby Cahill
It is widely known, metals, like all other pure substances, have melting points and boiling points, of which are extremely high, with the highest melting point being Tungsten’s at around 3422 ºC. The amount of energy required to break these metallic bonds through heating depends on the strength of the electrostatic forces. To transition from solid to liquid state, the temperature of the metal increases gradually before coming to a stop at its melting point. In this time where the temperature stops increasing, internal energy within the metal increases, breaking the bonds in the substance to form a liquid state. This process takes longer for metals with stronger electrostatic forces as more energy is required to overcome them. To transition from a liquid to a gaseous state, the metal would have to reach extreme temperatures and sustain its boiling point to allow the internal energy to increase and fully break the electrostatic forces between atoms and achieve gaseous metals.
You may not believe it but, metal vapours are used in many industries. One key example of this is in sodium-vapour lamps, often used in street-lights. Inside the lamp, a current is applied through an electrode in one end of the filament. The energy supplied from this initiates a low pressure arc that takes place in an inert gas mixture (typically neon and argon). The mixture gradually heats up the sodium into its excited state, combatting its inability to sustain the gaseous state for long periods of time naturally, and preventing further reaction from occurring. In low pressure sodium lamps, this produces a yellow-orange colour that releases little heat, making it more energy efficient, however the colour can be changed by converting this lamp to a high pressure one, which commonly has a brighter and whiter light. This is achieved by increasing the internal pressure of the lamp and often including other metals such as mercury. One disadvantage of a high pressure lamp is that it releases more heat than a low pressure sodium lamp, making it less efficient. The monochromatic light seen in low pressure sodium lamps restricts its use to outdoor areas, like in streetlights, whereas the brighter light seen in high pressure lamps makes it more common in industrial and sports lighting. Unfortunately, these fascinating lamps are gradually being replaced with LEDs in the UK, leaving the signature yellow glow of streetlights as a memory of the past. On the bright side, the exemption of the use of mercury in high pressure sodium lamps has been extended to 24th February 2027, so keep an eye out, because if you’re lucky, you might just find one.
To conclude, while pure metals can reach a gaseous state at extremely high temperatures, it is very unlikely that they should stay in this state without reacting with other substances. A common condition required to keep metals as vapours is the presence of the noble gases, as explained in the workings of sodium vapour lamps. So, although it may not be as easy as bringing metal to flame, metal vapours do exist, and they’re all around us.
- Ruby Cahill
