Grade 11

Grade 11


S-block elements (alkali and alkaline earth metals)


Introduction to s-block elements

The s-block elements are located on the left side of the periodic table. They are made up of two groups: group 1, which includes the alkali metals, and group 2, which includes the alkaline earth metals. These elements are characterized by having their outermost electrons in the s-orbital.

General characteristics of s-block elements

The s-block elements have several distinctive properties:

  • They are metallic in nature.
  • They are highly reactive, especially the alkali metals.
  • They are good conductors of electricity and heat.
  • They have low ionization energy and low electronegativities.

Alkali metals (Group 1 elements)

The alkali metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs) and francium (Fr). They have one electron in their outermost shell, which gives them their distinctive properties.

Characteristics of alkali metals

  • They are soft and can be cut with a knife.
  • Their melting and boiling points are lower compared to other metals.
  • They have low densities; for example, lithium, sodium, and potassium are less dense than water.
  • They quickly turn black when exposed to air due to the formation of a layer of metal oxide.

Example reaction of alkali metals

When alkali metals react with water, they form alkaline solutions with the evolution of hydrogen gas. For example, sodium reacts with water as follows:

2Na + 2H2O → 2NaOH + H2

Trends in the alkali metals

As you move from lithium to francium in group 1:

  • The atomic and ionic radii increase.
  • The ionization energy decreases as the distance of the outer electron from the nucleus increases.
  • Reactivity increases as the ionization energy decreases, making it easier to lose the outer electron.

Alkaline earth metals (Group 2 elements)

The alkaline earth metals include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra). These elements have two electrons in their outermost shell.

Characteristics of alkaline earth metals

  • They are harder than the alkali metals.
  • Their melting and boiling points are higher than those of alkali metals.
  • They are denser than the alkali metals.
  • They form colorless compounds unless the anion itself is colored.

Example reactions of alkaline earth metals

Alkaline earth metals also react with water, but less vigorously than alkali metals. Magnesium reacts with water as follows:

Mg + 2H2O → Mg(OH)2 + H2

Trends in alkaline earth metals

As you move from beryllium to radium in group 2:

  • The atomic and ionic radii increase.
  • The ionization energy decreases.
  • Reactivity increases, although not as dramatically as with the alkali metals.

Visual example

Bohr model of sodium (Na)

No

In this diagram, the nucleus is in the center, surrounded by two electron shells. Sodium's valence electrons are in the outer shell.

Bohr model of magnesium (Mg)

Milligrams

For magnesium, we see two electrons in the outer shell, which is typical for an alkaline earth metal.

Applications of s-block elements

Both alkali and alkaline earth metals have various applications in industry and daily life:

  • Sodium (Na): It is used in street lighting, in sodium vapor lamps, and in the production of various compounds such as sodium hydroxide and sodium carbonate.
  • Potassium (K): Important in biological functions, used in fertilizers and to make some types of glass.
  • Magnesium (Mg): It is used in the making of light alloys, flash photography, and as a reducing agent in the production of titanium.
  • Calcium (Ca): Essential for living organisms, especially in cell physiology, and used to make cement and mortar.

Conclusion

The s-block elements, which include the alkali and alkaline earth metals, play a vital role in chemistry and have important applications in a variety of fields. Their properties are greatly affected by their electronic configuration, and understanding these can provide important information about their reactivity and uses.


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