Alkali metals are a group of elements in the periodic table that have some unique and interesting properties. These elements, which include lithium, sodium, potassium, rubidium, cesium, and francium, are known for their reactivity and are often referred to as the most reactive metals.
The alkali metals have several physical properties that are characteristic of metals. They have a silver luster and are good conductors of heat and electricity. They are also ductile and malleable, meaning they can be drawn into wires and hammered into thin sheets. One of the most notable physical properties of alkali metals is their low melting points. Lithium has the highest melting point at 179°C while cesium has the lowest at 28.5°C. The alkali metals also have low densities compared to other metals. Lithium is the lightest metallic element.
Each alkali metal atom has a single electron in its outermost shell, which is much more weakly bound than those in inner shells. This valence electron is responsible for the reductive alkali metals that react easily with highly oxidizing substances such as oxygen and halogens. Alkali metals become active from top to bottom in the periodic table duo to their increased radius, and the reaction rate is increased from lithium to cesium gradually.
Alkali metals react vigorously with oxygen to form oxides. Lithium and sodium form monoxides while the heavier alkali metals form superoxides. Rubidium and cesium burn immediately when exposed to air even at room temperature.
Alkali metals also react with halogens to form salts known as alkali metal halides. Alkali metals become active from top to bottom in the periodic table, and halogens on the contrary, so the reaction is not the same. Such as the most active alkali metal Cs (not taking into account the radioactive Fr) and the most oxidizing fluorine gas meets immediately and violently explode. When Li placed in Cl₂, only the LiCl in the surface layer, difficult to have a clear reaction. They must be ignited to have a significant reaction.
When alkali metals react with water, they produce hydrogen gas and metal hydroxides. These reactions are highly exothermic and can be quite violent. The greater the mass of the alkali metal, the more violent the chemical reaction, and hydrogen may ignite and even explode.
The hydroxides formed by alkali metals are white crystals that are hygroscopic and readily soluble in water. They generate large amounts of heat upon dissolution and their solubility increases with the increasing atomic number. All alkali metal hydroxides are strong bases, meaning they dissociate completely in solution to give OH⁻ ions.