S-block elements are those whose last valence electron enters the outermost s-orbital. These elements belong to Group 1 (Alkali Metals) and Group 2 (Alkaline Earth Metals) of the periodic table. Due to their unique electronic configuration, these elements exhibit high reactivity, metallic character, and strong electropositive nature.
This article provides an in-depth exploration of:
- The electronic configuration of alkali and alkaline earth metals.
- The trends in properties across these groups.
- Their importance in chemical reactions and applications.
-images-1.jpg "Alkali & Alkaline Earth Metals – Electronic Configuration & Properties")
Understanding the S-Block Elements
What Are S-Block Elements?
S-block elements have their outermost electrons in the s-orbital. They have:
- Group 1 (Alkali Metals): One electron in the outermost shell (ns¹).
- Group 2 (Alkaline Earth Metals): Two electrons in the outermost shell (ns²).
Electronic Configuration Overview
| Group | General Electronic Configuration | Valence Electrons |
|---|---|---|
| Group 1 (Alkali Metals) | ns¹ | 1 |
| Group 2 (Alkaline Earth Metals) | ns² | 2 |
The number of valence electrons determines reactivity, ionization energy, and bonding behavior.
Group 1: Alkali Metals
Members & Their Electronic Configuration
| Element | Period | Electronic Configuration |
|---|---|---|
| Lithium (Li) | 2nd | [He] 2s¹ |
| Sodium (Na) | 3rd | [Ne] 3s¹ |
| Potassium (K) | 4th | [Ar] 4s¹ |
| Rubidium (Rb) | 5th | [Kr] 5s¹ |
| Cesium (Cs) | 6th | [Xe] 6s¹ |
| Francium (Fr) | 7th | [Rn] 7s¹ (Radioactive) |
Key Properties of Alkali Metals
- Highly Reactive – They lose one electron easily to form M⁺ (monovalent cations).
- Soft Metals – Can be cut with a knife (except lithium).
- Low Density – Lithium, sodium, and potassium are less dense than water.
- Low Melting & Boiling Points – Due to weak metallic bonding.
- Form Strong Alkali Hydroxides – Example:
- Stored in Kerosene – To prevent reaction with air and moisture.
Trends in Group 1
| Property | Trend Down the Group |
|---|---|
| Atomic size | Increases |
| Ionization energy | Decreases |
| Density | Increases |
| Reactivity | Increases |
Group 2: Alkaline Earth Metals
Members & Their Electronic Configuration
| Element | Period | Electronic Configuration |
|---|---|---|
| Beryllium (Be) | 2nd | [He] 2s² |
| Magnesium (Mg) | 3rd | [Ne] 3s² |
| Calcium (Ca) | 4th | [Ar] 4s² |
| Strontium (Sr) | 5th | [Kr] 5s² |
| Barium (Ba) | 6th | [Xe] 6s² |
| Radium (Ra) | 7th | [Rn] 7s² (Radioactive) |
Key Properties of Alkaline Earth Metals
- Less Reactive Than Alkali Metals – Due to a higher nuclear charge.
- Harder and Denser – Compared to alkali metals.
- Higher Melting & Boiling Points – Due to stronger metallic bonding.
- Form Basic Oxides & Hydroxides – Example:
- Found in Minerals & Ores – Essential for biological and industrial applications.
Exception: Beryllium (Be)
- Does not behave like typical alkaline earth metals.
- Forms covalent compounds rather than ionic.
- Has a high melting point due to strong covalent bonding.
Trends in Group 2
| Property | Trend Down the Group |
|---|---|
| Atomic size | Increases |
| Ionization energy | Decreases |
| Density | Increases |
| Reactivity | Increases |
Chemical Reactions of S-Block Elements
Reactions of Alkali Metals
- With Water:
- With Oxygen:
- With Halogens:
Reactions of Alkaline Earth Metals
- With Water:
- With Oxygen:
- With Acids:
Applications of S-Block Elements
| Element | Application |
|---|---|
| Lithium (Li) | Batteries, psychiatry (mood stabilizers) |
| Sodium (Na) | Salt, soap, glass industry |
| Potassium (K) | Fertilizers, fireworks |
| Magnesium (Mg) | Medicine, fireworks, alloys |
| Calcium (Ca) | Cement, bones, glass |
| Barium (Ba) | X-ray imaging, fireworks |
Frequently Asked Questions (FAQs)
Q1: Why are alkali metals stored in kerosene?
Alkali metals react violently with air and water, so they are stored in kerosene to prevent unwanted reactions.
Q2: Which alkali metal is the most reactive?
Francium (Fr) is the most reactive, but due to its radioactive nature, Cesium (Cs) is considered the most reactive stable alkali metal.
Q3: Why is beryllium different from other Group 2 elements?
Beryllium has a small atomic size and high ionization energy, making it covalent rather than ionic. It also does not react with water.
Q4: Why do alkali metals have low melting points?
Alkali metals have weak metallic bonding due to the presence of only one valence electron, making them soft with low melting points.
Q5: How do alkaline earth metals contribute to human health?
- Calcium is crucial for bones and teeth.
- Magnesium is important for muscle and nerve function.
