Difference Between Alkali Metals and Alkaline Earth Metals

Main Difference – Alkali Metals vs  Alkaline Earth Metals

All the elements on earth can be categorized into metals, non-metals, metalloids and inert gasses. Inert gasses are the elements with zero reactivity due to the presence of stable outermost octet. Metalloids are the elements that possess certain properties of both metals and non-metals. Non-metals are the elements that do not possess any property of metals. Metals are the elements that have some unique set of properties including, excellent electricity and thermal conductivity, and luster. Metals are placed on the left-hand side and middle part of the periodic table. All the metals in the periodic tables are classified into three groups, namely; alkali metals, alkaline earth metals, and transition metals. The main difference between alkali metals and alkaline earth metals is that alkali metals have one valence electron in the outermost orbit whereas alkaline earth metals have two valence electrons in the outermost orbit.

This article examines,

1. What are Alkali Metals
       – Definition, Characteristics, Properties, Examples
2. What are Alkaline Earth Metals
      – Definition, Characteristics, Properties, Examples
3. What is the difference between Alkali Metals and Alkaline Earth Metals

What are Alkali Metals

Alkali metals are the elements that possess only one valence electron in their outermost shell. These metals are placed in Group IA of the periodic table. These metals include lithium, sodium, potassium, rubidium, cesium and francium. By donating the single electron in the outermost shell to an electron-accepting atom, these metals become positively charged and obtain the electronic configuration of a noble gas. All the alkali metals are ionic and show electrovalency. The electron-donating tendency increases down the group since the positively charged nucleus has less attraction forces towards the outermost electron due to the presence of more electron filled inner shells. Unlike most of the other metals, the alkali metals are soft with low densities and low melting points. These metals are the most reactive of all the metals on the periodic table.

What are Alkaline Earth Metals

Alkaline earth metals are metals that have two valence electrons in their outermost shell. There are six alkaline earth metals, including beryllium, magnesium, calcium, strontium, barium and radium. They become stable by gaining the electron configuration of noble gasses through the donation of their outermost electrons. When the electrons are given away to an electronegative atom, the alkaline earth metals become positively charged. Alkaline earth metals are highly reactive metals and are placed in the second column of the periodic table. These metals are the building blocks for everything in the world. These metals are often found in the form sulfates in nature. Examples include the minerals such as gypsum; calcium sulfate, epsomite; magnesium sulfate and barite; barium sulfate.

Figure 1: Periodic table showing alkali and alkaline earth metals

Difference Between Alkali Metals and Alkaline Earth Metals

Number of Electrons in the Outermost Shell of an Atom

Alkali Metals: Each alkali metal has a single electron.

Alkaline Earth Metals: Each alkaline earth metal has two electrons.

Nature of the Metal

Alkali Metals: Alkali metals are soft.

Alkaline Earth Metals: Alkaline earth metals are hard.

Melting Points

Alkali Metals: Alkali metals have low melting points.

Alkaline Earth Metals: Alkaline metals have relatively high melting points.

Nature of the Metal Hydroxide

Alkali Metals: Hydroxides of alkali metals are strongly basic.

Alkaline Earth Metals: Hydroxides of alkaline earth metals are relatively less basic.

Decomposition of Carbonates

Alkali Metals: Carbonates of alkali metals do not decompose.

Alkaline Earth Metals: Carbonates of alkaline earth metals decompose to form oxide when heated to high temperatures.

Heating of Nitrates

Alkali Metals: Nitrates of Alkali metals give corresponding nitrates and oxygen as products.

Alkaline Earth Metals: Nitrates of alkaline earth metals give corresponding oxides, nitrogen dioxide and oxygen as products.

Stability of Hydroxides on Heating

Alkali Metals: Hydroxides of alkali metals are stable.

Alkaline Earth Metals: Hydroxides of alkaline earth metals form oxides.

Nature of Bicarbonates at Room Temperature

Alkali Metals: Bicarbonates of alkali metals exist in solid form.

Alkaline Earth Metals: Bicarbonates of alkaline earth metals exist in solution form.

Formation of Peroxides on Heating

Alkali Metals: Alkali metals form peroxides when heated.

Alkaline Earth Metals: Alkaline earth metals except Barium do not form peroxides.

Formation of Nitrides

Alkali Metals: Alkali metals do not form nitrides except for Lithium.

Alkaline Earth Metals: Alkaline earth metals form stable nitrides.

Formation of Carbides

Alkali Metals: Alkali metals do not form carbides except for Lithium.

Alkaline Earth Metals: Alkaline earth metals form stable carbides.

Examples

Alkali Metals: Lithium, sodium, potassium, rubidium, cesium and francium are examples of alkali methods.

Alkaline Earth Metals: Beryllium, magnesium, calcium, strontium, barium and radium are examples of alkaline earth metals.

Summary

Alkali metals and alkaline earth metals important elements that contain single and double valence electrons respectively in their outermost shell of an atom. The main difference between alkali metals and alkaline earth metals is the number of electrons in their outermost shells of atoms and subsequently their position in the periodic table. Alkali metals (lithium, sodium, potassium, rubidium, cesium and francium) are placed on the first column (IA) while alkaline earth metals (beryllium, magnesium, calcium, strontium, barium and radium) are placed on the second column (IIA) of the periodic table. Both metal groups are highly reactive. All these metals can be identified using the flame test as these metals exhibit a unique flame color when the metals are heated over a flame.

References:
1. Trefil, J. S. (2001). Encyclopedia of science and technology. Taylor & Francis.
2. Bridget Heos (2010). The alkaline earth metals: beryllium, magnesium, calcium, strontium, barium, radium, New York: Rosen Central.
3. Raymond Fernandes (2008). Living science Chemistry for class 10, Ratna Sagar P. Ltd.

Image Courtesy:
1.”Periodic table of the elements” By Le Van Han Cédric – LeVanHan (GFDL) via Commons Wikimedia