Appendix A
Electronic Structure of Atoms, Covalent Bonds, and Oxidation
Number of an Atom in a Compound
We recall here some basic concepts relevant to the class of reactions named
“redox,” in which the oxidation state of some elements is changed. Some reference
concepts and rules are categorized below. Only elements frequently encountered in
this Book are discussed.
i. The elements are classified on the basis of their “atomic number”- Z, that
corresponds to the number of protons in the nucleus, which equals the
number of electrons in the neutral species. H has 1 proton and 1 electron and
atomic number 1, C has Z = 6, N has Z = 7, O has Z = 8.
ii. Electrons are distributed over different energy levels, K, L, M, N…
iii. Each level is divided into sub-levels: K > only one sublevel named s; L >
two sublevels, s and p. M has three sublevels: s, p, d. We stop here as we
shall deal with atoms with valence electrons in levels K and L in the ground
state. Sub levels s, p, d are called orbitals (see Fig. A.1): each has a different
space geometry. There is a single s orbital with a spherical symmetry, three
separated p orbitals (along the three coordinated axes x, y, z), five d orbitals.
In general, a level “n” has a number of sub energy levels equal to n
2 .
Therefore, when n = 1 >> 1
2 >> 1 only one sub-energy level is possible and
this is labeled: “s” or 1s; when n = 2 >> 2
2 >> 4 sub energy levels are
possible labeled: 2s 2p x 2p y 2p z ; when n = 3 >> 3
2 >> 9 sub-energy levels are
possible labeled: 3s, 3p x 3p y 3p z 3d z 2, 3d x2-y2 3d xy 3d xz 3d yz .
Each orbital can be occupied by two electrons, each with a different number
of spin, or direction of rotation around its own axis (rotation to the wright or
to the left). Therefore, to each energy level can belong 2 Â n
2 electrons (and
as much different elements, each characterized by a different atomic number
Z): Level K with n = 1 is completed with 2 Â 1
2 = 2 element (H [1s
1 ], He
[1s
2 ]); Level K is said to be the first Period in the Periodic Table (see
Appendix J) and is completed with 2 elements. When n = 2 (or L) we have
the second Period that is completed with 2 Â 2
2 = 8 elements (Li, Be, B, C,
N, O, F, Ne). The third Period is completed with 18 elements (n = 3 >> 2 Â
© Springer Nature Switzerland AG 2021
M. Aresta and A. Dibenedetto, The Carbon Dioxide Revolution,
https://doi.org/10.1007/978-3-030-59061-1
229
Electronic Structure of Atoms, Covalent Bonds, and Oxidation
Number of an Atom in a Compound
We recall here some basic concepts relevant to the class of reactions named
“redox,” in which the oxidation state of some elements is changed. Some reference
concepts and rules are categorized below. Only elements frequently encountered in
this Book are discussed.
i. The elements are classified on the basis of their “atomic number”- Z, that
corresponds to the number of protons in the nucleus, which equals the
number of electrons in the neutral species. H has 1 proton and 1 electron and
atomic number 1, C has Z = 6, N has Z = 7, O has Z = 8.
ii. Electrons are distributed over different energy levels, K, L, M, N…
iii. Each level is divided into sub-levels: K > only one sublevel named s; L >
two sublevels, s and p. M has three sublevels: s, p, d. We stop here as we
shall deal with atoms with valence electrons in levels K and L in the ground
state. Sub levels s, p, d are called orbitals (see Fig. A.1): each has a different
space geometry. There is a single s orbital with a spherical symmetry, three
separated p orbitals (along the three coordinated axes x, y, z), five d orbitals.
In general, a level “n” has a number of sub energy levels equal to n
2 .
Therefore, when n = 1 >> 1
2 >> 1 only one sub-energy level is possible and
this is labeled: “s” or 1s; when n = 2 >> 2
2 >> 4 sub energy levels are
possible labeled: 2s 2p x 2p y 2p z ; when n = 3 >> 3
2 >> 9 sub-energy levels are
possible labeled: 3s, 3p x 3p y 3p z 3d z 2, 3d x2-y2 3d xy 3d xz 3d yz .
Each orbital can be occupied by two electrons, each with a different number
of spin, or direction of rotation around its own axis (rotation to the wright or
to the left). Therefore, to each energy level can belong 2 Â n
2 electrons (and
as much different elements, each characterized by a different atomic number
Z): Level K with n = 1 is completed with 2 Â 1
2 = 2 element (H [1s
1 ], He
[1s
2 ]); Level K is said to be the first Period in the Periodic Table (see
Appendix J) and is completed with 2 elements. When n = 2 (or L) we have
the second Period that is completed with 2 Â 2
2 = 8 elements (Li, Be, B, C,
N, O, F, Ne). The third Period is completed with 18 elements (n = 3 >> 2 Â
© Springer Nature Switzerland AG 2021
M. Aresta and A. Dibenedetto, The Carbon Dioxide Revolution,
https://doi.org/10.1007/978-3-030-59061-1
229