When you hear the word metal, the picture that comes to mind is of something rigid, shiny, and cold object used in building large sturdy structures. Or do you think about the liquid metal cooling in the latest PS5? If not, then you might think of iron, copper, or steel. Yes, that’s the general picture of metals. But they are substances which can have three physical states. Have you ever thought of metals in their liquid form? If you did, it is probably in their hot molten, and glowing state.
But opposing that concept, certain few metals can also be found in their liquid state at normal temperature. Note that, in chemistry room temperature means 25 ˚C. But in general terms, it can have a wide range. So, metals that melt at a slightly higher temperature were also included.
The question comes to mind, why are they different? To know the answer, we have to know about metallic bonds, the bond between metal atoms. If you’re curious, many chemistry study documents explore this in detail. Here is a brief description.
Metallic Bond
The characteristic of metals is just so that they neither completely give up nor hold in their outer shell electrons. As a result, their atoms create a matrix where they form positive ions and are surrounded by electrons. Think of a chunk of metal. In that chunk, there are numerous metal ions submerged in a sea of electrons which are loosely bonded to their atoms.
Those who have a slightly stronger attraction to electrons produce stronger metallic bonds and thus are solid at normal temperature. Most of the metals are this way. But a few have so little attraction that they produce very weak bonds and thus easily melt at normal temperature.
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Let’s stop talking about metallic bonds already and check out the very interesting stuff that liquid metal is.
Fireworks are one of the most beautiful things made by humans. But did you know that the colors of it are due to metal salts? One such metal is rubidium which is used to produce violet-red colored fire. And it is also one of the metals of today’s topic.
5. Rubidium (Rb)
Rubidium (Rb) is an alkali metal of the 5th period with an atomic number of 37. It is just below the potassium in the periodic table. It has a melting point of 39.3 ˚C (102.74 ˚F), a bit above our body temperature. It is not found readily in its liquid form but if you consider countries with a very hot climate you may find it in the liquid state under normal condition. Thus, rubidium was able to make a place for itself in the list of metals that are liquid at room temperature.
When not in liquid form it is so soft that you can easily cut it with a kitchen knife. It has a common silvery-white appearance. The name rubidium originates from the Latin word rubidius, which means deep red. You might be thinking, how in the world red and rubidium is related. It is because the atomic spectrum of rubidium has unique red lines. Although rubidium is not that well known and does not have that much use, it still has few very important uses.
The color of the flame of rubidium chloride (RbCl) is violet-red and so it is used in fireworks to produce beautiful violet colors. Fireworks are short-lived. But the isotope rubidium-87 has a half-life of 49 billion years which is 3 times the age of the universe. You may forget the sense of time while looking at beautiful fireworks. So, you would want to look at your clock to check the time. While you are happy if your clock is accurate to minutes, scientists need clocks that are more sensitive and accurate. And the isotope rubidium-87 does just that. It is used in atomic clocks due to its extremely high accuracy. Rubidium is also used in treating depression.
Even though rubidium sounds so good you must be careful around it. It is the second most electropositive metal on earth. It is so reactive that it will self-ignite in open air by reacting with atmospheric oxygen. It also reacts explosively with water. For this reason, rubidium is stored in an inert atmosphere or submerged in dry oil e.g., kerosene.
Enough with rubidium. Let’s check out our next liquid metal.
4. Gallium (Ga)
Gallium (Ga) has a melting point of 29.76 °C (85.57 °F). Although like rubidium it also has a melting point above room temperature, it is not that high. And it even melts in your hand. So, gallium’s position in this list is well deserved.
The phrase “melts in the mouth” is just perfect for this element. Wait, don’t try it. Gallium is not toxic in a small amount. But there is little knowledge. Guess, it doesn’t taste that good then. Still don’t try it.
Gallium sits just below aluminum in the periodic table with an atomic no of 31. And has a silvery-white appearance. Its discoverer, Paul-Emile Lecoq de Boisbaudran named it after the Latin word ‘gallus’ meaning ‘Gaul’ which is the old name of France, his homeland. Although some believed he named it after himself as both gallus and Lecoq mean rooster, this idea was denied.
Like aluminum, it has also proven its importance through many uses. When someone gets a fever, what you do first is to measure the temperature using a thermometer. What has gallium got to do here? You have guessed it correctly. Gallium is used in thermometers instead of mercury. Mercury is toxic whereas gallium can melt in the mouth. I would definitely choose gallium over mercury.
There are many other substances that can be used in thermometers. But gallium can do much more. At this age, there is no way you have not heard about semiconductors. Yes, gallium is one of the very few elements that is used to produce semiconductors. If you have a computer, you probably know what a solid-state drive is. The successor of hard-disk drives which are many times faster and more durable while much smaller. Don’t be surprised. Gallium semiconductor is used to make those fast storage devices.
Not everyone likes techs and things like these. But they sure do like to watch a good magic trick. Or even better, do a magic trick and get everyone’s praises. And gallium can help you do just that. Want to know how? A magician never reveals his secret. But hey I am no magician. The trick is called the vanishing spoon trick. For this, you need a spoon made of gallium metal. Act as if you are making tea for your friends and now stirring the warm tea with a ‘spoon’. Voila, the submerged part of the spoon is gone. Isn’t it fun to look at friends’ stupefied faces? 
Is that you, T-1000?
Not only this, gallium is used in a fun experiment called beating heart where it literally beats like a living thing. Science sure is fun and interesting and of course amazing. Won’t you agree?
Ah, there is one more important use of gallium which is to make alloys, solid solutions. As gallium is liquid it can easily dissolve a lot of other metals. Try putting gallium on a soda can. Be sure to remove any paint coatings. And see the magic.
There are many more fun and important uses of gallium but others are waiting in line.
So, let’s hurry and move on to our next metal on the list.
3. Cesium (Cs)
(IUPAC name – Caesium)
Our next metal in the list, the one that has been hailed as the most electropositive element on earth, is none other than cesium (Cs). It has a melting point of 28.5 °C (83.3 °F), which is almost equal to that of gallium. But don’t ever try taking it even in your hands. You will know why in a bit. It has atomic no 55 and has the 2nd lowest position in group-I which is just below rubidium. As a metal from the same group, it has lots of similarities with rubidium. They are just like brothers. The name cesium comes from the Latin ‘coesius’ which means sky-blue. Like rubidium, cesium got its name from the color of atomic spectral lines which are blue. But unlike other group-I metals, it has a pale gold appearance.
As you have read earlier, cesium and rubidium are like brothers but cesium is like the older one. More ductile, more reactive, more electropositive, and thus more hazardous. The explosions it creates while reacting with water is so violent that it can even break the vessel if it is made of glass.
And yeah, cesium too is used in atomic clocks, specifically, the cesium-133 isotope is used. But it is more accurate. In fact, it is the most accurate measurement humans have ever achieved. This fact is a lot more than it sounds. It has so little error that it would take 20 million years for a cesium clock to deviate by just 1 second. How cool is that!!
Not just that. The very unit “a second” is defined in terms of cesium! The time it takes for cesium to complete 9 192 631 770 ground-state transitions is equal to one second. Imagine, for every second that passes, a cesium atom vibrates 9 192 631 770 times.
Cesium has four isotopes among which only cesium-133 is stable while others are radioactive. And the use of cesium mostly involves its radioactivity.
You saw that the melting point decreases as we go down the group-I metals. And cesium is the 2nd lowest metal. So, shouldn’t the lowest metal have an even lower melting point? And yes, our next metal is francium, the last member of group-I.
2. Francium (Fr)
Francium was discovered in France by Marguerite Perey in 1939 and was named after the country. It is situated in group-I, period-7 In the periodic table. Just below cesium.
It is the second rarest naturally occurring element on earth. It is radioactive and has a very short half-life. Even the most stable isotope francium-223 has a half-life of only 22 minutes. It is naturally produced through the decay of actinium but itself decays into astatine, radium, and radon. It is found in trace amounts with uranium ores. Believe it or not, you can find only about an ounce (20-30 grams) of francium in the earth’s crust at any given time but that would also decay. And only a few hundred thousand atoms were synthesized by humans. You would have to pay billions of dollars only to get a few grams of this substance. And so, not much about francium is known.
It has a melting point that is uncertain and estimated to be 8.0 °C (46.4 °F). You may think that francium should have been the most electropositive metal instead of cesium. But it has been predicted that its radioactivity might interfere which on contrary will lower the electropositive nature.
Being so rare, it has no commercial applications. It has been used in scientific research only. Scientists also tried to apply it in cancer diagnosis but it was found to be impractical.
We might not know a lot about francium. But our next and last metal has been familiar to humans since a long time ago. And it is none other than mercury.
1. Mercury (Hg)
Mercury is the top liquid metal on earth. It is the only metal that is liquid at standard temperature and pressure (0 ˚C, 1 atm). It has a melting point of −38.82 °C (−37.89 °F) which, as you can see, is way lower than even water.
It is a transition metal with an atomic number 80 and an atomic mass of 200.592. It has a shiny silvery appearance and so it is also called quicksilver. It is named after planet mercury due to its high speed. The Latin name of mercury, hydrargyrum, comes from the Greek word hydrargyros which literally means water-silver.
Although mercury is not very reactive and does not react with most acids, it is very toxic for humans and other animals. It accumulates in the body and causes various diseases and mercury poisoning. But It has a lot of uses in our daily life.
Mercury was familiar to humans since as early as 1500 BCE. And still is heavily used. It might surprise you, but it is a rare metal. The major source of mercury is cinnabar, an ore of sulfur (HgS) which is also called red mercury because of its color.
When you hear mercury, you probably think of a thermometer. As you already know mercury is liquid under normal conditions. And luckily, its volume changes uniformly with temperature which makes it a suitable material for thermometers. But it has a lot of other uses. The ancient people produced red pigment called vermillion using cinnabar. And It was of great importance in alchemy. Although it might shock you, mercury was therapeutically used until as late as the 18th century. More shocking, people believed that drinking mercury prolongs life which on the contrary caused them an early death. Ironic, isn’t it?
Although in decline, mercury is used a lot. The first thing that comes to mind after the thermometer is the air pressure. Atmospheric pressure is also expressed in mmHg units ( 1atm=760mmHg). And thus, mercury is used in the barometer, the device used to measure the pressure of atmospheric pressure. It is used in making fluorescent light also known as neon signs. The major use of mercury is in the PVC industries of China. And it is China that is the major supplier of mercury. You have already read about atomic clocks. The fact that they are super accurate is amazing but the downside is their large size. Accuracy of time is very important in space for astronauts and other spacecraft. Luckily NASA has developed an ultra-precise miniaturized atomic clock using mercury which albeit not as accurate as of the cesium clock, is much smaller.
You might have already guessed that liquid metal mercury must have contributed to producing alloys (metal solutions). You are right. Mercury forms amalgams, Meaning alloys of mercury, with almost all metals except iron. You can even extract gold using mercury as a solvent. An interesting fact is that mercury is not allowed to carry on planes because of how easily it forms an amalgam with aluminum, the major component of a plane’s structure. Did you already know that? Well, now you know. If you know someone who likes sweets and candies too much and unfortunately caused cavities, you might know dentists use a type of paste as filling. Don’t be surprised, mercury is used to make that paste.
All the known forms of mercury are harmful and toxic. We now end this list wishing you to be safe from harmful chemicals.
But before going let’s know a bit more about liquid metal in general. Although the existence of liquid metal has been known to humans for a long time, this property has been mostly used for producing alloys and nothing much. But now more work is being done on this property. You might have already understood that common properties of metal such as conducting heat or electricity would not be the same for the liquid state. The liquid metal processor coolers for high-end computers or the latest model of PlayStation, PS5 are just the beginning.
With the desire to serve more interesting and amazing content, Goodbye!!
