Difference Between Alkali and Alkaline

Main Difference – Alkali vs Alkaline

Alkali and alkaline earth metals are basic elements, and the compounds they form are also basic compounds. When added to water, the solutions show pH values higher than pH 7. These compounds are used for different purposes such as neutralizing or reducing the acidity of a medium. Alkali metals are the group 1 metals of the periodic table whereas alkaline earth metals are in the group 2. The main difference between alkali and alkaline is that alkali metals have one valence electron whereas alkaline earth metals have two valence electrons.

Key Areas Covered

1. What is Alkali
      – Definition, Properties, Examples
2. What is Alkaline
      – Definition, Properties, Examples
3. What are the Similarities Between Alkali and Alkaline
      – Outline of Common Features
4. What is the Difference Between Alkali and Alkaline
     – Comparison of Key Differences

Key Terms: Alkali, Alkali Metals, Alkaline, Alkaline Earth Metals, Periodic Table, pH, Valence Electrons

What is Alkali

The term alkali is used to name the group 1 elements of the periodic table (Lithium, sodium, potassium, etc.). These elements are known as alkali metals. The basic compounds formed from these elements are alkali compounds. An alkali compound is a substance that can form OH^– ions when added to water. Therefore, alkali compounds dissolve in water to give solutions having values higher than pH 7. All alkalis have pH values greater than 7. These are basic compounds.

Alkali substances can turn the color of red litmus into blue color. They can also react with acidic compounds giving a salt and water as the end products. Hence, alkali substances can be used to neutralize an acidic solution. Alkali metals are very soft (we can cut sodium easily using a knife). These elements have one valence electron in the outermost orbital. Therefore, they are very reactive elements. They can form +1 cations by removing the valence electron.

In the concentrated form of alkali, they are corrosive and can cause skin irritations. The most common alkalis include hydroxides and carbonates. The reaction between an acid and a hydroxide will give a salt and water. The reaction between an acid and a carbonate gives a salt, water, and carbon dioxide gas.

Figure 1: Sodium Hydroxide

Examples

Sodium hydroxide (NaOH)
Potassium hydroxide (KOH)
Lithium oxide (Li₂O)
Ammonia (NH₃)

What is Alkaline

The term Alkaline is used to name group 2 elements of the periodic table (Magnesium, calcium, strontium, etc.). These are known as alkaline earth metals. These compounds also form OH^– ions when added to water. The solutions of alkaline compounds have higher pH values (>7).

These alkaline compounds also can turn red color litmus into blue. They have basic properties. Alkaline earth metals are harder than alkali metals. These elements form +2 cations because they have two valence electrons and, a cation can be formed by removing those electrons. However, since these electrons are in the s orbital as an electron pair, these elements are not that much reactive.

Figure 2: Comparison of Atomic Radii of Alkali and Alkaline Earth Metals

Alkaline earth metals have a lower atomic radius than alkali metals. This is because the number of electrons and protons are higher than the adjacent group 1 elements.

Similarities Between Alkali and Alkaline

Both have basic properties.
Both can turn red litmus into blue color.
Both types of compounds can form aqueous solutions having >7pH.
Both can form OH^– ions when added to water.

Definition

Alkali: The term Alkali is used to name the group 1 elements of the periodic table.

Alkaline: The term Alkaline is used to name group 2 elements of the periodic table.

Physical Properties

Alkali: Alkali metals are soft.

Alkaline: Alkaline earth metals are hard.

Valence Electrons

Alkali: Alkali elements have one valence electron.

Alkaline: Alkaline earth metals have two valence electrons.

Cations

Alkali: Alkali metals form +1cations.

Alkaline: Alkaline earth metals form +2 cations.

Ionization Energy

Alkali: Alkali metals have a lower ionizing energy.

Alkaline: Alkaline earth metals have a higher ionizing energy.

Conclusion

Alkali metals are the elements in the group 1 of the periodic table. Alkaline earth metals are the elements in the group 2. Both have basic properties. When added to water, both can form solutions having higher pH values (>pH). The main difference between alkali and alkaline is that alkali metals have one valence electron whereas alkaline earth metals have two valence electrons.

References:

1. Helmenstine, Anne Marie. “What Does Alkaline Mean?” ThoughtCo, Available here.
2. “Alkali.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 14 Jan. 2014, Available here.
3. “GCSE Bitesize: Alkalis.” BBC, Available here.

Image Courtesy:

1. “SodiumHydroxide” By Walkerma – Own work (Public Domain) via Commons Wikimedia
2. “Atomic radius of alkali metals and alkaline earth metals” By DePiep – Own work (CC BY-SA 3.0) via Commons Wikimedia