Did you know that the elements in the periodic table are further classified on the basis of their properties? Well, depending on the nature of reaction that the metals display, some of the metals are called Alkali metals. Making such classification is sometimes vital to the understanding of different elements.
It also helps us in determining the expected outcome of a given element, based on its placement in the periodic table. Hence, studying alkali metals and their properties is very interesting and stimulating to the overall knowledge of the periodic table. Let us understand more about these metals.
Alkali Metals – Group 1 Elements
Included in the Group 1 of the periodic table are the following elements:
The general electronic configuration of Group 1 elements is ns1. They have a strong tendency to donate their valence electron in the last shell to form strong ionic bonds. They have the least nuclear charge in their respective periods. As we move down the group, the atomic radius increases. Therefore, the nuclear charge decreases. Caesium is the most metallic element in the group.
In order to prevent the elements from coming in contact with oxygen, they are stored in jars that contain oil. The melting points of these elements are quite low, which is 180° Celsius in the case of Lithium, while it is 39° Celsius in the case of Rubidium. When it comes to the density of the metal, group one elements display a very low level of density of up to 1 gcm-3 which means that they can easily float on the surface of the water.
Therefore, if we decide to cut these metals, we will be able to do so, without much trouble. Upon being cut into two halves, we can observe that their surface is as shiny as any other metal but even after they are stored in oil, they undergo tarnishing. As a conductor of heat and electricity, they are excellent.
Learn more about Group 14 Elements here.
The Reaction of Alkali Metals with Water
Alkali metals derive their classification because of the results of their reaction with water. It is known upon the reaction with water that alkali metals produce an alkaline solution, along with the release of hydrogen gas. The following chemical equations demonstrate how various metals react with water:
lithium + water → lithium hydroxide + hydrogen
2 Li(s) + 2 H2O(l) → 2 LiOH (aq) + H2(g)
sodium + water → sodium hydroxide + hydrogen
2 Na(s) + 2 H2O(l) → 2 NaOH (aq) + H2(g)
potassium + water → potassium hydroxide + hydrogen
2 K(s) + 2 H2O(l) → 2 KOH (aq) + H2(g)
All elements in a particular group react in an analogous manner.
How Do Alkali Metals React Otherwise?
Labelled as the most reactive group of metals in the periodic table, each of the alkali metals is capable of reacting with different elements to produce different results. Following chemical equations demonstrate some of the ways in which they react:
potassium + oxygen → potassium oxide
4 K(s) + O2(g) → 2 K2O(s)
sodium + chlorine → sodium chloride
2 Na(s) + Cl2(g) → 2 NaCl(s)
potassium + chlorine → potassium chloride
2 K(s) + Cl2(g) → 2 KCl (s)
All alkalis manifest themselves as a white solid in their compound form that is capable of being dissolved in water. Most of these compounds are ionic in nature.
Learn about Group 16 Elements here.
The History of Alkali Metals
Alkali metal salts were known to the ancients through the Old Testament which refers to a salt called ‘Neter’ (sodium carbonate), extracted from the ash of vegetable matter. Saltpetre (potassium nitrate) was used in gunpowder, which was invented in China around about the 9th century AD and had been introduced into Europe by the 13th century.
In October in the year 1807, the English chemist Sir Humphry Davy isolated potassium and later sodium. The name sodium comes from the Italian soda, a term applied in the Middle Ages to all alkalis, potassium comes from the French ‘potasse’, a name used for the residue left in the evaporation of aqueous solutions derived from wood ashes.
In the year 1817 Swedish chemist Johan August Arfwedson discovered Lithium while analyzing the mineral petalite. The name lithium comes from lithos, the Greek word for stony. The element was not isolated in pure form until Davy produced a minute quantity by the electrolysis of lithium chloride.
Learn more about Group 17 Elements here.
A Solved Question for You
Q: What are the properties of alkali metals?
Ans: Alkali metals are highly reactive in nature, which is why they manifest themselves in combination with other elements, in nature. Most of these metals are easily soluble in water, which makes their extraction quite easy. All alkali metals show a silver-like lustre, which makes them appear shiny. They are highly ductile and conduct electricity without any trouble.
All alkali metals have a very low melting point and the alloys of such alkali metals display even lower melting points. They react most easily with the oxygen in the atmosphere and water vapor. They are also capable of reacting quite vigorously to form hydrogen gas and strong caustic solutions.