The elements of Groups 1 and 2 of the periodic table are called s-block elements. They include alkali and alkaline earth metals. They are called s-block because their valence electrons lie in the s orbital ^[1-4].

Electron Configuration

Group 1 Elements

The Group 1 elements or alkali metals have one electron in their valence shell. Their electron configuration ends in ns¹, where n is the period number. A list of Group 1 elements, their chemical symbols, and electron configurations are shown below ^[1-4].

Element Name	Chemical Symbol	Electron configuration
Hydrogen	H	1s1
Lithium	Li	[He] 2s1
Sodium	Na	[Ne] 3s1
Potassium	K	[Ar] 4s1
Rubidium	Rb	[Kr] 5s1
Cesium	Cs	[Xe] 6s1
Francium	Fr	[Rn] 7s1

Group 2 Elements

The Group 2 elements or alkaline earth metals have two electrons in their outermost shell with an electron configuration ending in ns². A list of Group 2 elements, with their chemical symbols and electron configurations, are shown below ^[1-4].

Element Name	Chemical Symbol	Electron configuration
Beryllium	Be	[He] 2s1
Magnesium	Mg	[Ne] 3s2
Calcium	Ca	[Ar] 4s2
Strontium	Sr	[Kr] 5s2
Barium	Ba	[Xe] 6s2
Radium	Ra	[Rn] 7s2

Note: Helium is considered an s-block element since its valence electrons lie in the 1s subshell. However, it is located in Group 18. Its electron configuration is 1s².

Properties ^[1-4]

Physical Properties

1. All the s-block elements are light metals except hydrogen, which is a non-metal. They are soft, silvery, shiny, and good conductors of electricity and heat.

2. The alkali metals have low melting and boiling points due to weak metallic bonding. They have low density, increasing Group 1 from Li to Cs. The exception is K, which is lighter than Na. Li is the lightest known metal. Fr is a natural element that can be found rarely on Earth.

3. The alkaline earth metals are harder than alkali metals. Due to their smaller sizes, their melting and boiling points are higher than the corresponding alkali metals.

Chemical Properties

1. The outermost electrons are loosely held to the atom. As a result, these metals quickly lose their valence electrons and are highly electropositive.

2. Alkali metals lose one valence electron and form a +1 oxidation state. Alkaline earth metals lose two valence electrons and form a +2 oxidation state.

3. Alkali and alkaline earth metals react vigorously with water to produce hydrogen gas. They must be stored carefully to prevent unnecessary reactions or even explosions.

4. Alkali metals react with hydrogen to produce hydrides. These hydrides react with water to form the corresponding hydroxides and hydrogen gas.

Example

2 Li + H₂ → 2 LiH

LiH + H₂O → LiOH + H₂

Alkali metals also form complex hydrides such as LiAlH₄.

5. Alkali metals react with oxygen to produce oxides and superoxide. Examples: Li₂O and Na₂O₂.

6. Fireworks are composed of s-block elements along with other substances. Their purple, red, and green colors are due to the ionic forms of potassium, strontium, and barium.

Diagonal Relationship

A diagonal relationship exists between the elements of the second and third periods. For instance, lithium in Group 1, Period 2 shows similar properties to magnesium in Group 2, period 3. Similarly, beryllium in Group 2, Period 2 shows similar properties to aluminum in Group 13, Period 3. Two elements showing identical properties are called diagonal pairs or diagonal neighbors ^[1-4].

Many similarities exist between lithium and magnesium, and one of them is the atomic size. The following table shows the atomic and ionic radii of the two elements.

Property	Lithium	Magnesium
Atomic radius	152 pm	160 pm
Ionic radius	76 pm	72 pm

Many similarities also exist between beryllium and aluminum. The ionic radius of Be²⁺ is 31 pm, and that of Al³⁺ is 50 pm. Both elements have nearly the same charge/radius ratio.