Alkali metals are the chemical elements present in Group 1 of the periodic table. The alkali metals contain: Sodium (Na), Lithium (Li), Rubidium (RB), Potassium (K), Francium (Fr) and Cesium (Cs). Hydrogen, while it looks to be listed within Group 1, is not included within the alkali metals because it rarely exhibits related behavior. The term alkali received its title from the Arabic word al qali, which means from ashes. These particular elements had been given the name Alkali since they react with water to make hydroxide ions, making a basic solution (pH>7), which are also referred to as alkaline solutions.
Facts about Alkali Metals
Alkali metals are recognized for being probably the most reactive metals. This is due in part for their larger atomic radii and reduced ionization energies. They often donate their electrons within reactions and usually have an oxidation state of +1. These types of metals are characterized as being very soft and silvery in color. Additionally they have low melting and boiling points and are less dense compared to most elements. Na, Li and K have the capacity to float on water due to their low density.
Beginning at the top we find hydrogen (H). But wait. That element is actually not in the family. When we said about families, we stated that they have been groups of elements that behave in similar ways. Hydrogen is a really special element of the periodic table and does not belong to any family. While hydrogen sits in Group I, it is not an alkali metal.
Hydrogen is positioned at the top of group 1 of periodic table. Its place however is not justified due to its resemblance with alkali metals and with halogens.
Hydrogen resembles with alkali metals in the following ways.
Both display oxidation state of +1 in their compounds.
Both alkali metals and hydrogen have a single electron in their outermost shell.
Both alkali metals and hydrogen are excellent reducing agents.
Both alkali metals as well as hydrogen form compounds with electronegative elements.
The alkali metals exhibit most of the physical properties typical to metals, even though their densities are less than those of other metals. Alkali metals possess one electron within their outer shell, which is freely bound. This provides them the biggest atomic radii of the elements in their respective periods. Their reduced ionization energies lead to their metallic properties and higher reactivities. An alkali metal can effortlessly lose its valence electron to make the univalent cation. Alkali metals have low electronegativities. They react quickly with nonmetals, particularly halogens.
Summary of Common Properties
One loosely bound valence electron
Lower densities compared to other metals
Low ionization energies
Biggest atomic radii in their periods