The key difference between alkali metals and alkaline earth metals is that all alkali metals have an electron in their outermost shell whereas all the alkaline earth metals have two outer electrons.
As both Alkali metals and alkali earth metals are the first two groups in the periodic table, the difference between alkali metals and alkaline earth metals is a subject of interest for any chemistry student. Alkali metals and alkaline earth metals are the “S-block” elements because elements in both of these groups have their outermost electron(s) in the s-subshell.
Both alkali metals and alkaline earth metals are good electrical and heat conductors. The elements in these two groups are the most reactive metals in the periodic table. Their melting points are relatively lower than other metals. Alkali metals and alkaline earth metals have many similar properties, but this article discusses mainly their differences.
CONTENTS
1. Overview and Key Difference
2. What are Alkali Metals
3. What are Alkaline Earth Metals
4. Side by Side Comparison – Alkali Metals vs Alkaline Earth Metals in Tabular Form
5. Summary
What are Alkali Metals?
The alkali metals are the elements present in the first group of the periodic table. They are Lithium (Li), Sodium(Na), Potassium (K), Rubidium (Rb), Cesium (Cs) and Francium (Fr). They are all metals and very reactive therefore none of these metals do not occur as free metals in nature. We should store these metals always in inert liquids such as kerosene because they rapidly react with the air, water vapour and oxygen in the air. Sometimes they explosively react with other substances. They can achieve the noble gas state easily, by removing the outermost electron in the valence shell.
The densities of Lithium and Sodium are less than the density of water. However, the other elements are denser than water. Many of alkali metal compounds (NaCl, KCl, Na2CO3, NaOH) are commercially very important.
What are Alkaline Earth Metals?
Alkaline earth metals are in the second group of the periodic table. Group II elements include; Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba) and Radium (Ra). Similar to alkaline metals, these elements also do not occur freely in nature and they are also very reactive.
Figure 01: Atomic Radius of Alkali and Alkali Earth Metals
All the elements in this group are denser than water. Pure metals have a silver-grey color, but they tend to decolorize quickly when exposed to air because they form an oxide layer on the surface. Same as alkali metals, these metals are also good conductors in heat and electricity. All of these metals are commercially valuable.
What is the Difference Between Alkali Metals and Alkaline Earth Metals?
Alkali metals are the elements present in the first group of the periodic table. Alkaline earth metals are in the second group of the periodic table. Alkali metals have the electronic configuration of [Noble gas] ns1 while Alkaline earth metals have, [Noble gas] ns2 electronic configuration. With regard to the valency of these metals, all alkali metals have an electron in their outermost shell. And all alkaline earth metals have two outer electrons.
Alkali metals have only +1 ionic charge in their compounds when alkaline earth metals have +2 ionic charges in their compounds. Comparatively, alkali metals are more reactive than alkaline earth metals. Moreover, alkali metals are very soft and they can be cut with a sharp knife. However, alkali earth metals are harder than the alkali metals.
Summary – Alkali Metals vs Alkaline Earth Metals
Alkali metals and the alkaline earth metals are the group I and group II elements in the periodic table respectively. The most significant difference between these two groups is the electronic configuration. It determines the valency of the elements. Therefore, the difference between alkali metals and alkaline earth metals is that all alkali metals have an electron in their outermost shell whereas all the alkaline earth metals have two outer electrons.
Reference:
1. Tepper, Frederick, and James L. Dye. “Alkali Metal.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 21 June 2017. Available here
2. “Alkaline Earth Metal.” Wikipedia, Wikimedia Foundation, 20 May 2018. Available here
Image Courtesy:
1.’Atomic radius of alkali metals and alkaline earth metals’By DePiep – Own work, (CC BY-SA 3.0) via Commons Wikimedia