Chapter 1
Molecules and Intermolecular
Interactions
1.1 Hierarchy of Materials
1.1.1 Energetic Overview of Nature
This book deals with the structure and properties of an ensemble of molecules.
Before proceeding into details, let us see the typical magnitude of energies involved
in various phenomena. It will be clear why such a description based on the identity
of molecules is appropriate and what extent it is to.
It is reasonable to start with nuclei of atoms. They are formed by nucleons (protons
and neutrons) through the strong interaction. Although hadrons, including nucleons,
are composed of quarks, the decomposition to quarks is impossible (known as the
quark confinement). The minimal nuclear reaction is the formation of a deuteron
from a proton and a neutron. This reaction accompanies the emission of a photon
(γ-ray) with the energy of ca. 2.2 MeV (1 eV is ca. 96.5 kJ mol
−1 ). According to
the equivalence of mass and energy revealed by Einstein, E = mc
2 (c is the speed
of light in vacuum), the binding energy ΔE for an arbitrary nucleus with Z protons
and N neutrons can be calculated from its mass defect ΔM as
ΔE = ΔMc
2
=
Z M p + N M n − M
c
2
,
(1.1)
where M p , M n , and M are masses of proton, neutron, and the nucleus, respectively.
Figure 1.1 shows the binding energy per nucleon (ΔE/(Z + N )). As seen in Fig. 1.1,
the binding energy is typically several MeV and shows the maximum (≈ 8.7 MeV)
for the nucleus of
56 Fe.
Each neutral atom consists of a nucleus and electrons, the number of latter which
accords to the charge compensation. The energy necessary to remove an electron from
an atom in the ground state is the (first) ionization energy. The ionization energy is,
within an excellent approximation, dependent not on the atom’s mass number but
© The Editor(s) (if applicable) and The Author(s), under exclusive license
to Springer Nature Singapore Pte Ltd. 2020
K. Saito, Chemical Physics of Molecular Condensed Matter,
Lecture Notes in Chemistry 104,
https://doi.org/10.1007/978-981-15-9023-8_1
1
Molecules and Intermolecular
Interactions
1.1 Hierarchy of Materials
1.1.1 Energetic Overview of Nature
This book deals with the structure and properties of an ensemble of molecules.
Before proceeding into details, let us see the typical magnitude of energies involved
in various phenomena. It will be clear why such a description based on the identity
of molecules is appropriate and what extent it is to.
It is reasonable to start with nuclei of atoms. They are formed by nucleons (protons
and neutrons) through the strong interaction. Although hadrons, including nucleons,
are composed of quarks, the decomposition to quarks is impossible (known as the
quark confinement). The minimal nuclear reaction is the formation of a deuteron
from a proton and a neutron. This reaction accompanies the emission of a photon
(γ-ray) with the energy of ca. 2.2 MeV (1 eV is ca. 96.5 kJ mol
−1 ). According to
the equivalence of mass and energy revealed by Einstein, E = mc
2 (c is the speed
of light in vacuum), the binding energy ΔE for an arbitrary nucleus with Z protons
and N neutrons can be calculated from its mass defect ΔM as
ΔE = ΔMc
2
=
Z M p + N M n − M
c
2
,
(1.1)
where M p , M n , and M are masses of proton, neutron, and the nucleus, respectively.
Figure 1.1 shows the binding energy per nucleon (ΔE/(Z + N )). As seen in Fig. 1.1,
the binding energy is typically several MeV and shows the maximum (≈ 8.7 MeV)
for the nucleus of
56 Fe.
Each neutral atom consists of a nucleus and electrons, the number of latter which
accords to the charge compensation. The energy necessary to remove an electron from
an atom in the ground state is the (first) ionization energy. The ionization energy is,
within an excellent approximation, dependent not on the atom’s mass number but
© The Editor(s) (if applicable) and The Author(s), under exclusive license
to Springer Nature Singapore Pte Ltd. 2020
K. Saito, Chemical Physics of Molecular Condensed Matter,
Lecture Notes in Chemistry 104,
https://doi.org/10.1007/978-981-15-9023-8_1
1