The p-Block Elements

General Trends of Group 15 Elements-Group B

Group 18 Elements

Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn)

All are gases.

Chemically uncreative − Hence, they are termed as noble gases.

Occurrence

Occur in atmosphere (except Rn)

Atmospheric abundance in dry air is ∼ 1%. (Argon is the major constituent)

Xe and Rn are the rarest elements of the group.

Rn is the decay product of 226Ra.

He and Ne are found in minerals of radioactive origin such as pitchblende, monazite, cleveite, etc.

Atomic Properties

General outer electronic configuration is ns2 np6.

Exception − He (1s2)

High ionisation enthalpy

Reason − Stable electronic configuration

However, ionisation enthalpy decreases down the group (that is, with the increase in atomic size).

Atomic radii increase down the group.

Large positive values of electron gain enthalpy

Reason − Stable electronic configurations

Physical Properties

Monoatomic

Colourless, odourless, and tasteless

Sparingly soluble in water

Low melting and boiling points.

He has the lowest boiling point of 4.2 K.

Unusual property of diffusing through most commonly used laboratory materials such as rubber, glass, or plastics

Question

Why do noble gases have very low boiling points?

Answer

Being monoatomic, they have no interatomic forces except weak dispersion force.

Hence, they are liquefied at very low temperature and they have low boiling points.

Chemical Properties

Less reactive

Reason:

Completely filled ns2 2p6 valence shell electronic configuration (Except He − 1s2)

High ionisation enthalpy and more positive electron gain enthalpy

First noble gas compound − Xe+PtF6−

Obtained by mixing PtF6 and Xe

Xenon-Fluorine Compounds

XeF2, XeF4, and XeF6

Obtained by the direct reaction of elements

XeF6 can also be obtained by the interaction of XeF4 and O2F2 at 143 K.

XeF4 + O2F2 XeF6 + O2

Properties

Colourless crystalline solids

Sublime at 298 K

Powerful fluorinating agents

Readily hydrolysed even by traces of water

Example:

Structure

XeF2 Linear

XeF4 Square planar

XeF6 Distorted octahedral

Chemical Properties

Xenon-Oxygen Compounds

Hydrolysis of XeF4 and XeF6 with water gives XeO3.

Partial hydrolysis of XeF6 gives XeOF4 and XeO2F2 (oxyfluorides).

Properties

XeO3 is a colourless explosive solid.

XeOF4 is a colourless volatile liquid.

Structure

XeO3 has a pyramidal molecular structure.

XeOF4 has a square pyramidal molecular structure.

Uses of Noble Gases

Helium

In filling balloons for meteorological observations as it is a non-inflammable and light gas

In gas-cooled nuclear reactors

Liquid Helium

As a cryogenic agent

As a diluent for oxygen in modern diving apparatus

Reason − Very low solubility in blood

To produce and sustain powerful superconducting magnets, which are essential parts of modern NMR spectrometers and MRI instruments

Neon

In discharge tubes and fluorescent bulbs

Neon bulbs − Used in botanical gardens and in green houses

Argon

To provide an inert atmosphere in high temperature metallurgical processes

For filling electric bulbs

In the laboratory for handling substances that are air-sensitive

Xenon and Krypton

In light bulbs designed for special purposes

Group 18 Elements

Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn)

All are gases.

Chemically uncreative − Hence, they are termed as noble gases.

Occurrence

Occur in atmosphere (except Rn)

Atmospheric abundance in dry air is ∼ 1%. (Argon is the major constituent)

Xe and Rn are the rarest elements of the group.

Rn is the decay product of 226Ra.

He and Ne are found in minerals of radioactive origin such as pitchblende, monazite, cleveite, etc.

Atomic Properties

General outer electronic configuration is ns2 np6.

Exception − He (1s2)

High ionisation enthalpy

Reason − Stable electronic configuration

However, ionisation enthalpy decreases down the group (that is, with the increase in atomic size).

Atomic radii increase down the group.

Large positive values of electron gain enthalpy

Reason − Stable electronic configurations

Physical Properties

Monoatomic

Colourless, odourless, and tasteless

Sparingly soluble in water

Low melting and boiling points.

He has the lowest boiling point of 4.2 K.

Unusual property of diffusing through most commonly used laboratory materials such as rubber, glass, or plastics

Question

Why do noble gases have very low boiling points?

Answer

Being monoatomic, they have no interatomic forces except weak dispersion force.

Hence, they are liquefied at very low temperature and they have low boiling points.

Chemical Properties

Less reactive

Reason:

Completely filled ns2 2p6 valence shell electronic configuration (Except He − 1s2)

High ionisation enthalpy and more positive electron gain enthalpy

First noble gas compound − Xe+PtF6−

Obtained by mixing PtF6 and Xe

Xenon-Fluorine Compounds

XeF2, XeF4, and XeF6

Obtained by the direct reaction of elements

XeF6 can also be obtained by the interaction of XeF4 and O2F2 at 143 K.

XeF4 + O2F2 XeF6 + O2

Properties

Colourless crystalline solids

Sublime at 298 K

Powerful fluorinating agents

Readily hydrolysed even by traces of water

Example:

Structure

XeF2 Linear

XeF4 Square planar

XeF6 Distorted octahedral

Chemical Properties

Xenon-Oxygen Compounds

Hydrolysis of XeF4 and XeF6 with water gives XeO3.

Partial hydrolysis of XeF6 gives XeOF4 and XeO2F2 (oxyfluorides).

Properties

XeO3 is a colourless explosive solid.

XeOF4 is a colourless volatile liquid.

Structure

XeO3 has a pyramidal molecular structure.

XeOF4 has a square pyramidal molecular structure.

Uses of Noble Gases

Helium

In filling balloons for meteorological observations as it is a non-inflammable and light gas

In gas-cooled nuclear reactors

Liquid Helium

As a cryogenic agent

As a diluent for oxygen in modern diving apparatus

Reason − Very low solubility in blood

To produce and sustain powerful superconducting magnets, which are essential parts of modern NMR spectrometers and MRI instruments

Neon

In discharge tubes and fluorescent bulbs

Neon bulbs − Used in botanical gardens and in green houses

Argon

To provide an inert atmosphere in high temperature metallurgical processes

For filling electric bulbs

In the laboratory for handling substances that are air-sensitive

Xenon and Krypton

In light bulbs designed for special purposes

Group 15 Elements

Nitrogen (N), Phosphorus (P), Arsenic (As), Antimony (Sb) and Bismuth (Bi)

Occurrence

Nitrogen

Comprises 78% of the atmosphere (by volume)

Occurs as sodium nitrate (NaNO3) and potassium nitrate (KNO3) in earth’s crust

Found in the form of proteins in plants and animals

Phosphorus

Occurs in minerals of the apatite family Ca9(PO4)6.CaX2 (X = F, Cl or OH), which are the main components of phosphate rocks Essential constituent of animal and plant matter Present in bones as well as in living beings Phosphoproteins are present in milk and eggs. Arsenic, antimony and bismuth are found mainly as sulphide minerals.

Atomic Properties

General valence shell electronic configuration is ns2np3

Covalent and ionic radii increase down the group

Ionisation enthalpy decreases down the group due to gradual increase in atomic size. Order of successive ionisation enthalpies: ΔiH1 < ΔiH2 < ΔiH3

Electronegativity decreases down the group, with increase in atomic size

Physical Properties

Polyatomic

N2 is a diatomic gas; all others are solids

Metallic character increases down the group