S Block Elements Physical & Chemical properties

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What are S-Block Elements?

The elements which contains outermost valence electrons in “s” sub-shell are known as s-block elements. Group I and II are known as s-block elements of the modern periodic table. Furthermore, they are also known as alkaline & alkaline earth metals. These metals on reacting with water produces alkaline solutions.

Let us take the example of Group I and II respectively.

Sodium (Na) & Magnesium (Mg) belongs to Group I and II respectively.

We know that the electronic configuration of these two elements are 11 & 12.

Let’s have a look on their electronic configuration.

Sodium (Na): 1s², 2s², 2p⁶, 3s²

The outermost valence electrons (3rd shell) are located in the s-subshell.

Magnesium (Mg): 1s², 2s², 2p⁶, 3s²

The outermost valence electrons (3rd shell) are located in the s-subshell.

Group I A Elements

Peculiar behaviour of s-block elements

The s-block elements include Group I & Group II elements respectively. The abnormal behaviour exhibited by these elements is chiefly due to:

1. Low atomic size as compared to other groups.
2. Greater polarization power due to high charge & low atomic size.
3. Absence of the vacant d-orbitals.

General properties

1. They react with nitrates ultimately producing nitrites.
2. They are highly electropositivity in nature.
3. All Monoxides & Hydroxides of Group I elements (Alkali metals) are basic in nature.
4. The alkali metals are soluble in polar solvents.
5. They exhibit metallic bonding which makes them suitable for conducting electricity.
6. Low Ionization Energy enables alkali elements to react vigorously with halogens (Group VIII elements).
7. Group I elements from Beryllium (Be) to Radium (Ra) exhibits different flame colours.

Atomical & Physical Properties

Trends in Atomic Radius: The atomic radius increases from Lithium (Li) to Cesium (Cs) due to the increase in the number of shells down the group.

Trends in Metallic Character: The metallic character of elements from Lithium (Li) to Francium (Fr) increases down the group due to high electropositivity.

Trends in First Ioniazation Energy: The first ioniazation energy from Lithium (Li) to Cesium (Cs) decreases down the group due to the increase in the atomical radius of the elements.

Trends in Electronegativity: The electronegativity from Lithium (Li) to Cesium (Cs) decreases down the group while the electropositivity increases down the group.

Trends in Melting & Boiling Points: The melting & boiling points from Lithium (Li) to Cesium (Cs) decreases down the the group due to the weak binding forces present between the atoms in their crystal lattice.

Trends in Density: The density from Lithium (Li) to Cesium (Cs) increases down the group. However, Potassium (K) is an exceptional case which is lighter than Sodium (Na).

Trends in Polarization Power: The polarization power (charge/area ratio) decreases from Lithium (Li) to Francium (Fr) down the group due to the increase in the atomic radius of the elements.

Trends in Hydration Enthalpy: The hydration enthalpy from Lithium (Li) to Cesium (Cs) decreases down the group due to the increase in the atmoic size of the elements. If an element has high hydration enthalpy, it usually attracts a huge amount of water molecules towards itself due to high charge attraction & low area (High polarization power).

Trends in Thermal Stability of Hydrogen Carbonates & Carbonates: The thermal stability of hydrogen carbonates & carbonates increases down the group due to increase in the polarization power.

Reactivity: The elements from Lithium (Li) to Francium (Fr) are highly reactive. They are kept closed from air contact by keeping them in certain solutions or tubes.

Nature: These alkali metals from Lithium (Li) to Francium (Fr) are soft & can be easily cut with a knife.

Valency: Their valency is 1 because they can lose only one electron to attain noble gas configuration. Their group number directly indicates the group elements valencies.

Peculiar Behaviour of Lithium (Li)

● It is one of the least reactive alkali metal compared to its group members.
● It only forms monoxides (Li2O) while reacting with Oxygen.
● It is a lot harder alkali metal of the Group I.
● It is a stronger reducing agent among all its group members.
● It reacts with Nitrogen forming nitrides but its other group members do not exhibit this character.
● It doesn’t forms ethynide from ethyne as compared to other alkali metals.
● It doesn’t forms solid hydrogen carbonates as compared to its group members.
● Only Lithium Carbonate (LiCO3) decomposes on heating while its group members do not exhibit this character.

Chemical Reactions with Water

The reactivity of Group I elements with water increases down the group. They all react with water forming metal Hydroxide & evolving Hydrogen gas. The general chemical formula is as follows.

X (s) + H2O (l) –> XOH (aq) + ½H2 (g)

The reaction shows that the solution formed becomes alkaline due to the presence of OH- ions.

Chemical Reactions with Oxygen

All alkali metals reacts Oxygen forming monoxides, peroxides & superoxides except Lithium (Li) which tends to form only monoxides. There is no general chemical formula for this reaction. However, you need to memorise every chemical reaction equation.

Chemical Reactions with Hydrogen

All Group I elements on reacting with Hydrogen produces their respective hydrides. The general chemical formula is as follows:

2X +2H –> 2XH

Chemical Reactions with Chlorine

All Group I elements react with Chlorine forming white solid chlorides. The general chemical formula is as follows.

2X (s) + 2Cl (g) –> 2XCl (s)

Flame Colours

Different colours are observed from Beryllium (Be) to Magnesium (Mg) due to the difference in the reflection & absorption of light wavelengths due to the excitation & de-excitation of electrons in the elements shells.

Uses

Alkali metals are used to make alloys. Ex: Sodium-potassium (NaK) alloy is composed of two alkali metals namely Sodium (Na) & Potassium (K) which is usually liquid at room temperature.
Sodium Carbonate (Na2CO3.10H2O) commonly known as “Washing Soda” which is soluble in water is used for cleaning purpose as well as for manufacturing glass.
Sodium (Na) is used commonly in kitchen salt. It is also an important component during nerve impulse transmission.
Sodium hydroxide (NaOH) commonly known as “Caustic Soda” is used in petroleum refinement & textile industries.
Potassium (K) regulates the opening & closing of stomata in the plant cells. Potassium hydroxide (KOH) generally works as a precipitating agent.
Radium (Ra) is commonly used to treat cancer cells.

Group II Elements

Trends in Atomic Radius: The atomic radius increases from Beryllium (Be) to Radium (Ra) down the group.

Trends in First Ionization Energy: The first ionization energy from Beryllium (Be) to Radium (Ra) decreases down the group.

Trends in Electronegativity: The electronegativity from Beryllium (Be) to Radium (Ra) decreases down the group.

Trends in Melting & Boiling Point: The melting & boiling points of Group II elements do not show any regular trend.

Trends in Thermal Stability: The thermal stability of Group II elements nitrates & carbonates increases down the group due to decreasing polarization power.

Valency: Their valency is 2 because they can lose only two electrons to attain noble gas configuration. Their group number directly indicates the group elements valencies.

General Properties

● They are highly elctropositive alkaline-earth metals.
● They are silvery soft elements which can also be cut easily with a knife.
● The elements of Group II also known as Alkaline-Earth metals exhibit 2 valency.
● The Alkaline-Earth metals exhibit metallic bonding which enables them to conduct electricity.
● They are strong reducing agents due to high electropositivity & low ionization energy.
● Group II elements from Beryllium (Be) to Radium (Ra) exhibits different flame colours.

Chemical Reactions with Water

The reactivity of Group II elements with water gradually increases down the group. They reacts slowly with water producing metal hydroxides & hydrogen gas respectively. The chemical formula is as follows:

X (s) + 2H2O (l) –> X(OH)2 (s) + H2 (g)

Chemical reactions with Oxygen

Group II elements react with Oxygen forming oxides. However, all elements from Beryllium (Be) to Radium (Ra) forms simple oxides but peroxides are formed only by Barium (Ba) & Strontium (Sr).

The chemical formula for simple oxides & peroxides is as follows.

Simple oxide: 2X (s) + 2O (g) — > 2XO (s)
Peroxide: X (s) + O2 (g) –> XO2 (s)

Chemical reactions with Nitrogen

Group II elements on reacting with Nitrogen forms white solids which are ionic in nature. The chemical formula is as follows.

3X (s) + N2 (g) –> X3N2 (s)

Effect on Heat of Carbonates

Group II elements from Beryllium (Be) to Radium (Ra) on heating decomposes to solid metal oxide & carbon dioxide gas. The chemical formula is as follows.

XCO3 (s) –> XO (s) + CO2 (g)

Peculiar Behaviour of Beryllium (Be)

Beryllium (Be) differs from its Group II members due to:

Small atomic size.
High polarization power.
High electronegativity & ionization energy as compared to its members.
Absence of vacant d-orbital in its valence shell.
Beryllium is a hard metal while other members of its group are relatively soft.
Melting/Boiling points of Beryllium are relatively higher than its group members.
Beryllium resists complete oxidation due to the formation of BeO coating.
Beryllium tends to form covalent bonds.
Salts of Beryllium doesn’t exhibit any characteristic flame colour.
Beryllium Oxide (BeO) is insoluble in water while the oxides of other members are soluble.

Beryllium (Be) Covalent Nature

Beryllium (Be) forms covalent bonds with many elements forming nitride, chloride, etc which are covalent in nature. This is chiefly due to smaller size & high polarization power.

Flame Colours

Different colours are observed from Lithium (Li) to Cesium (Cs) due to the difference in the reflection & absorption of light wavelengths due to the excitation & de-excitation of electrons in the elements shells.

Uses

● Magnesium (Mg) is an essential component in the activity of enzymes & for the synthesis of ATP.
● It is also used in flares, fireworks, sparklers, etc.
● Calcium (Ca) is highly important for blood clotting.
● Calcium Oxide (CaO) commonly known as Quick Lime on hydrolysis forms Calcium Hydroxide which has an disinfectant property widely used for the sewage treatment.

Diagonal Relationship between s-block elements

There exists diagonal relationship in the modern periodic table. Group I and II or First period and Second period adjacent elements exhibits similarities. Their well known similarities are mentioned below.

Similarities between Beryllium (Be) & Aluminium (Al)

The s-block elements Beryllium (Be) & Aluminum (Al) shows physical & chemical similarities between each other. Some of the characteristic properties has been mentioned below:

● The elements Beryllium (Be) & Aluminium (Al) hydroxides are amphoetric in nature.
● Beryllium (Be) & Aluminum (Al) due to their amphoetric character reacts with alkali producing Beryllate & Aluminate.
● Beryllium (Be) & Aluminum (Al) hydroxides react with alkali producing salts & respective ions.
● The elements Beryllium (Be) & Aluminium (Al) both reacts with nitric acid
● These metals have the ability to form complexes containing ligands. Beryllium (Be) & Aluminium (Al) are soluble in organic solvents.
● Beryllium (Be) & Aluminum (Al) oxides do not react with acids due to the presence of oxide layer on its surfaces.
● They are strong reducing agents due to high electropositivity & low ionization energy.

Similarities between Lithium (Li) & Magnesium (Mg)

The s-block elements Lithium (Li) & Magnesium (Mg) shows physical & chemical similarities between each other. Some of the characteristic properties has been mentioned below:

● They have low atomic size as compared to other s-block elements.
● Lithium & Magnesium reacts gently with water forming oxides & hydroxides.
● Lithium & Magneisum are hard metals as compared to its group members.
● These oxides & hydroxides are less soluble in water.
● Hydroxides of Lithium & Magnesium are weak bases which can be easily decomposed on heating.
● Lithium & Magnesium exhibit covalent character.
● They react with nitrogen forming their nitrides (Lithium & Magnesium nitrides) respectively. Lithium (Li) & Magnesium (Mg) do not form superoxides.
● Lithium & Magnesium Chlorides (LiCl & MgCl2) are soluble in ethanol.
● They are strong reducing agents due to high electropositivity & low ionization energy.

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