Placed at the leftmost side of the periodic table, the alkali metals are crucial in the S-Block elements. Since alkali metals lose electrons, they are one of the most reactive elements present on the earth. Alkali elements include Lithium(Li), Sodium(Na), Rubidium (Ru), Cesium (Cs), Potassium (K), and Francium (Fr). Note that Francium readily loses electrons; therefore, it is the most reactive with a low half-life.

Metals	Lithium	Sodium	Potassium	Rubidium	Cesium
Atomic Number	3	11	19	37	55
Configuration	[He]2s1	[Ne]3s1	[Ar]4s1	[Kr]5s1	[Xe]6s1
Abundance (ppm)	65	28300	25900	310	7
Atomic size (pm)	152	186	227	248	265
Density g/cm3	0.53	0.97	0.86	1.53	1.9
Ionization energy kJ/mol	520	496	419	403	376
Hydration enthalpy kJ/mol	-506	-406	-330	-310	-276
Reduction potential (v)	-3.04	-2.714	-2.925	-2.930	-2.927
Flame colour	Crimson red	Yellow	Violet	Red Violet	Blue

General Characteristics of the Compounds of the Alkali Metals 

General Characteristics of the Compounds of the Alkali Metals are as follows- 

• Alkali metals are soft metals to the extent that these can be easily cut through knives. As alkali metals come down the group, their hardness keeps on increasing. 
• Alkali metals, especially Francium, are highly reactive in nature. 
• These metals have low boiling as well as melting points. 
• Out of all the alkali metals, sodium is vastly found as its least reactive of all; however, Francium is rarely found as it keeps on losing electrons. 
• If tested with fire, each alkali metal produces different colours, such as Lithium with flame shows red colour.

Anomalous Properties of Lithium are as follows- 

• In group one, lithium is one of the hardest metals present. 
• As compared to other group-one metals, lithium has higher boiling and melting point. 
• Lithium is the least reactive of all.
• If reacted with Ethyne, lithium remains the same. 
• When lithium nitrate is heated, it gives rise to lithium oxide, Li2
  4LiNO3 --> 2Li2O + 4NO2 + O2.

When Sodium is reacted to other elements of the modern periodic table, it gives rise to other useful compounds such as halides, sulfate, nitrate, carboxylates, and carbonates. 

• Sodium carbonate (Na2CO3.10H2O) is commonly known as washing soda. 
• Sodium chloride, obtained by evaporating sea water. 
• Sodium hydroxide or caustic soda can be formed by two different chemical processes: causticizing and electrolytic. 
• Sodium hydrogen carbonate, popularly known as baking soda, has a molecular formula of NaHCO3.

Biological Importance of Sodium and Potassium

Biological Importance of Sodium- 

• Sodium ions are commonly present in nerve cells in the human body responsible for regulating the flow of water. 
• To transport sugar in human cells, sodium plays a significant role. 
• Sodium keeps the body hydrated and helps in meeting the electrolyte levels in the body. 

Biological Importance of Potassium- 

• Potassium ions are generally found inside the human cells 
• They are responsible for keeping a check on the opening and closing of stomata. 
• They play a significant role in the functioning of the heart, skeleton, and muscle contraction. 
• Regular intake of potassium maintains the electrolyte balance in the human body.

Belonging to the group 2 of the modern periodic table, it contains elements like beryllium, magnesium, strontium, barium, calcium, and radium. All elements of alkaline earth metals or group 2 are the same in their physical and chemical properties.

Metals	Beryllium	Magnesium	Calcium	Strontium	Barium
Atomic Number	4	12	20	38	56
Configuration	[He]2s2	[Ne]3s2	[Ar]4s2	[Kr]5s2	[Xe]6s2
Abundance (ppm)	6	20900	36300	300	250
Atomic size (pm)	112	160	197	215	222
Density g/cm3	1.85	1.74	1.55	2.63	3.62
Ionization energy kJ/mol	899 & 1757	737 &1450	590&1146	549&1064	503&965
Hydration enthalpy kJ/mol	-506	-406	-330	-310	-276
Reduction potential (v)	-1.7	-2.37	-2.87	-2.89	-2.9
Flame colour	–	–	Brick red	Crimson red	Apple green

General Characteristics of Compounds of the Alkaline Earth Metals 

• Alkaline earth metals are generally silver and white.
• Although alkaline earth metals are soft, when compared to other alkali metals, these are way harder. 
• They have high boiling and melting points. 
• When infused with flame, they produce colors like brick red, apple green, and so on.

Anomalous Behaviour of Beryllium

• Beryllium has a higher melting point than other Alkaline earth metals. 
• Beryllium does not react with water. However, other metals do. 
• As compared to other metals in group 2, beryllium is harder.

Some Important Compounds of Calcium

• The other name of calcium oxide (CaO) is quick lime. 
• When calcium carbonate is heated, it forms carbon dioxide and calcium oxide. 
• When decomposed, it gives rise to calcium oxide and carbon dioxide.
• When calcium oxide is reacted with carbon dioxide, it gives rise to calcium carbonate.
• Calcium carbonate is used in preparing cement.

Biological Importance of Magnesium and Calcium

Biological Importance of Magnesium- 

• Proper functioning of enzymes. 
• Magnesium is responsible for keeping human DNA safe.
• Magnesium produces energy within the body. 
• Magnesium maintains the level of electrolytes in the body. 

Biological Importance of Calcium-  

• Calcium is found in human teeth and bones 
• Blood stores loads of calcium 
• Muscle contraction is the result of calcium deficiency in the human body 
• Calcium ensures blood clotting after an injury; otherwise, it may lead to extreme blood loss.

How many elements are in as-block? 

There are 14 elements in an S-Block including hydrogen (H), lithium (Li), sodium (Na), beryllium (Be), helium (He), potassium (K), magnesium (Mg), rubidium (Rb), francium (Fr), barium (Ba), calcium (Ca), cesium (Cs), strontium (Sr), and radium (Ra). 

What are s-block elements and their properties? 

Chemistry Class 11 S-Block comprises 14 elements. Compared to other elements, these are extremely soft and can be cut through a knife with low boiling and melting points. 

What are the classifications of S block elements?

Class 11 S-Block elements are classified into two, including the Alkali Metals known as group one and Alkaline Earth Metals known as group 2.