Definitions [2]
Definition: Alkali Metals
The Group 1 elements (Li, Na, K, Rb, Cs, Fr) are collectively called alkali metals. All elements except Hydrogen in this group are called alkali metals.
Definition: Alkaline Earth Metals
The Group 2 elements (Be, Mg, Ca, Sr, Ba, Ra) are called alkaline earth metals. They are less reactive than alkali metals. Radium (Ra) is the first radioactive element in this group, discovered by Madame Curie.
Key Points
Key Points: Alkali Metals
Electronic Configurations:
| Period | Element | Symbol | Atomic No. | Electronic Configuration |
|---|---|---|---|---|
| 2 | Lithium | Li | 3 | [He] 2s¹ |
| 3 | Sodium | Na | 11 | [Ne] 3s¹ |
| 4 | Potassium | K | 19 | [Ar] 4s¹ |
| 5 | Rubidium | Rb | 37 | [Kr] 5s¹ |
| 6 | Caesium | Cs | 55 | [Xe] 6s¹ |
| 7 | Francium | Fr | 87 | [Rn] 7s¹ |
Periodic Trends in Group 1
| Property | Trend Down the Group |
|---|---|
| Atomic radius | Increases |
| Ionic radius | Increases |
| Density | Irregular trend |
| Ionisation enthalpy | Decreases (lower IE → more reactive) |
| Melting point | Decreases |
Biological Importance
- Na⁺ ions participate in the transmission of nerve signals
- High concentration of Na⁺ and low concentration of K⁺ is found in blood plasma
- High concentration of K⁺ and low concentration of Na⁺ is found inside human cells
- K⁺ ions are essential for nerve impulse transmission and maintaining osmotic balance
Uses of Alkali Metals
- Lithium is used in lithium-ion batteries
- Potassium is used in manufacturing potassium superoxide (KO₂) for oxygen generation in submarines, mountaineering, and space equipment
- Potassium chloride is used as a fertilizer
- Be is used as a moderator in nuclear reactors
Key Points: Alkaline Earth Metals
Electronic Configurations:
| Period | Element | Symbol | Atomic No. | Electronic Configuration |
|---|---|---|---|---|
| 2 | Beryllium | Be | 4 | [He] 2s² |
| 3 | Magnesium | Mg | 12 | [Ne] 3s² |
| 4 | Calcium | Ca | 20 | [Ar] 4s² |
| 5 | Strontium | Sr | 38 | [Kr] 5s² |
| 6 | Barium | Ba | 56 | [Xe] 6s² |
| 7 | Radium | Ra | 88 | [Rn] 7s² |
Periodic Trends in Group 2:
| Property | Trend Down the Group |
|---|---|
| Atomic radius | Increases |
| Ionic radius | Increases |
| Density | Irregular trend |
| Ionisation enthalpy (1st and 2nd) | Decreases up to Ba |
| Melting point | Irregular trend |
Importance of Alkaline Earth Metals
- Mg²⁺ ions are a constituent of chlorophyll — the green pigment in plants responsible for photosynthesis
- Ca²⁺ ions play a vital role in blood clotting (coagulation cascade)
- Ca²⁺ is essential for the formation and strength of bones and teeth (as calcium phosphate)
- Mg²⁺ is required for the activity of many enzymes in the body
- Ca²⁺ ions are involved in muscle contraction and nerve signal transmission
- Sr and Ba compounds are generally toxic to biological systems
