Covalent Bonds Creation between Gas and Liquid Phase Change: Compatibility with Covalent and Even-Odd Rules Based on a “Specific Periodic Table for Liquids”

A 
decrease in temperature will eventually turn a gas into liquid and then into a 
solid. Each of these phase change shows a higher degree in cohesion of 
molecules. While it is usually admitted that molecules in solids form 
additional connections, the cohesion of molecules in liquids is usually 
explained by changes in kinetics of molecules. Given that the density of a 
solid is nearly the same than that of a liquid, the present paper assumes a 
different stand and considers that connections between molecules must be similar 
in liquids and in solids. The difference between gas, in which molecules are entirely loose, and liquid, is therefore 
the presence of an additional connection between gaseous molecules. This paper 
describes how and where these connections are built with the help of a few 
rules and a “specific periodic table for liquids”. The coherence of this 
approach is reinforced by its capacity to explain phase change of forty 
well-known molecules containing inorganic and organic elements.


Introduction
Molecules in gases are totally free from one another and they fill the entire volume they are offered. Small variations in pressure or temperature do not modify the structure of gaseous molecules. On the opposite, in the solid state, molecules are predominantly held together through several covalent bonds. Thanks to these bonds, the solid is uncompressible and no internal movement is possible. In the intermediate state, liquid, the medium is fluid like in a gas, but incompressible like a solid. However, the reason for this is not clearly explained in scientific publications [1]. The objective of this paper is to propose a model of the liquid state. It will give a detailed chemical understanding of what happens when gases become liquids.
The main idea exposed here, is that a liquid is formed when physical conditions are reached for molecules to build their first covalent bonds. In other words, liquefaction occurs when some atoms of two gaseous molecules connect with a new covalent bond. The liquid is hence composed of molecules held to one another through a unique covalent bond. This structure remains unchanged until physical conditions impose the formation of other covalent bonds, inducing a change into solid state.
After giving a few rules to root our concept, we will explain here that this bond holding liquid molecules together is composed of an electron pair coming from the inside of an atom. It will be shown that liquefaction transformations maintain electrical neutrality of molecules. To finally demonstrate its simplicity and logic, the concept is applied to forty well-known molecules [1].
In the present article: -compounds are in the form of molecules therefore ions are excluded, -each atom in a compound is either neutral or with a single, positive or negative, charge [2], -atoms are represented by their acronyms as in the classical periodic table [3], -the drawing of a small line between two atoms represents a covalent bond [4] [5], -to remain conform to notations used in previous papers dealing with the even-odd rule, compounds are noted in capitals: NH3 is for neutral ammonia, NH4(+) for ammonium and NH2(−) for amide ions [4] [5].

Tools and Rules
We expose here a few rules and a specific table for chemistry that will be used in explaining how a covalent bond is created between molecules to form a liquid [6].

Even-Odd Rule: Basic Concepts of Atoms in a Compound
Molecules are composed of atoms linked through bonds. These bonds are covalent bonds composed of electron pairs [7]. In former publications, a rule named even-odd rule has been described and clarifies how many covalent bonds an atom erects [4]. This rule has successfully been applied to small molecules with central neutral atoms [4], then to ions with a central charged atom [5].
Noteworthy for the present article, atoms only erect single bonds with neighboring atoms and never with multiple bonds [8]. This modification (compared to classical theory) has a direct consequence on positions of charged atoms in a compound [9]. The procedure also asserts that atoms are neutral or with only a single charge [2].
This rule depends on the number of electrons an atom has in a compound. Briefly recalled, it states that: -Neutral even atoms have an even number of bonds, -Neutral odd atoms have an odd number of bonds, -Atoms with single charge have a reversed parity of the numbers of bonds compared to neutral atoms. Lastly, this rule is equally applied to compounds having organic and/or inorganic atoms [10].

Covalent Bonds Rule
In a compound, atoms are classically related to each other by some different ways [11]. Although classical theory has introduced many different types of intermolecular forces, the underlying concept in all past articles, as well as in the present one, is that connections between atoms are always covalent. These covalent bonds are: -composed of one electron pair [12] -with only a single covalent bond between two connected atoms [8] -connecting two neutral atoms or one neutral atom to a single charged atom or two different charged atoms [12] -not allowed to connect atoms having the same positive or negative charge [12].

Electronic Structure of an Atom in a Compound
The electronic structure of an atom in a compound can be described as In this electronic structure, the total number of electrons of an atom in a compound is always even. This occurs whatever the electrical charge of the compound and whatever the current phase (solid, liquid or gaseous) [12]. Such electronic structures have been tested on well-known crystals [13] [14].

Periodic Table for Liquids
To simplify the understanding of the structures, a specific periodic table was introduced [12]. This table indicates numbers of bonds for an atom and the influence of the charge [10] [12]. The enhanced periodic table has been tested against chemical dissociation of medium sized molecules [15]. Unfortunately, this peri-odic   This "specific periodic table for gas to liquids transformations" will be very useful to follow changes of numbers of bonds and charges positions during chemical transformations.

Molecular Connections from Gas to Liquid
Some molecules can be represented with atoms A and B, with groups of atoms R1 R2 R3, and with lines for covalent bonds as follow: In this drawing, single atoms A or B are connected by covalent bonds to groups R. These last groups are composed of atoms structured by covalent bonds between neighboring atoms. They can have any number of atoms.
A liquid is formed when several gaseous molecules establish a new connection with a covalent bond. Starting with the previously described molecules, these connected molecules can be drawn as follow: Atoms B and A are now connected with a covalent bond. It can be said that an association has occurred. This association may form very large molecules. These large molecules can move slowly in liquids, but they cannot be compressed.
Consequently, a liquid is made of many large molecules, like these ones, as in organic oils [16].

Electrons' Positions in Molecules
Chemistry of a molecular association depends on the parity of atoms A and B which interact [2]. Three options are possible: even-even, odd-odd and even-odd.
In the three-following drawing: electrons form pairs which are represented by a line ended by two points. When composing a bond, each point represents an electron which belongs to only one atom, but they are still composing a covalent bond.
In the following drawings, symbol n is an even number and symbol m has the parity of its nucleus.

Two Even Atoms to be Associated
In gas and liquid phases, electrons positions between two even atoms can be drawn as: In this drawing, electron pairs are shown below the nucleus in three shells: an inner shell with n electrons, an inactive shell with m electrons and a covalent shell.
In the inner shell, the number of electrons is not changed by the gas to liquid transformation. This is different for electron pairs of the inactive shell [10].
Covalent shells in the two first atoms have two electron pairs forming two covalent bonds: with R1 and R2 for atom A; with R2 and R3 for atom B.
To build a group with one covalent bond, an electron pair of the inactive shell of atom B must move: number (m2-2) becomes (m2-4) in B(+). This pair appears in two covalent shells: one electron in A and the other electron stays in B but in its covalent shell. Atom B has lost one electron and has become B(+). Atom A has received one electron from B and has become A(−). The total number of electrons is unchanged, as expected.

Odd Atoms
In gas and liquid, electron positions between odd atoms can be drawn as: In this drawing, left atom B has one missing electron and atom A has one added. This is necessary to keep electrons pairs everywhere around each nucleus of the compounds.
In this drawing, as in the previous one, the number of electrons in the inner shell is not changed by the transformation. In the inactive shells, m is odd and to obtain even numbers, they must be changed as: (m2-3) and (m1-1) into (m2-3) and (m1-3).
When A and B are gathered (right side in this drawing), both atoms are uncharged and have a new covalent bond. One electron of atom A has moved into the covalent shell of atom B. The other electron has moved into the covalent shell of atom A. This electron pair has not been destroyed and their covalence is still valid.

One Odd and One Even Atoms
Electrons positions between an odd atom and an even atom in gas to liquid transformation can be drawn as: Consequently, from all these drawings, in gas to liquids transformations, only two atoms are concerned and the number of bonds for these coupled atoms is always increased by one.

Application: Gas to Liquid Transformations
In this chapter, gaseous molecules and liquid structures are drawn. Structures of molecules are well-known [1] [6] [17], but their liquids structures are not. Table 2  Table 2. Molecules in gaseous and liquid phase with their temperature in liquid phase. Column 1 gives the couple of atoms going to be associated for liquid formations. Column 2 gives the name of compounds allowing the formations of these bonds. Column 3 gives the number of bonds of the atoms before and after the liquid transformation and the temperature range of the liquid phase. Column 4 shows the drawings of the gas and the liquids using the molecule of column 2.    tries to propose such liquid structures which are deduced from the gaseous one using rules described in this article.
In Table 2, molecules names are listed in column 2 and the drawings of about 40 molecules are in column 4 in which gases are drawing above the structure of its liquid phase.
To lower the number of drawn molecules in this paper, only atoms coming from the two first rows of the classical periodic table are used. Table 2 can be read as follow: -The first column indicates the two atoms concerned by the formation of a new bond involved in the three other columns of the same row.
-The second column gives the name and the formula of the concerned molecules. -The third column gives the number of bonds implied before and after the gas transformation into a liquid. It also gives the temperature range where molecules are in a liquid form (˚C). -The fourth column shows drawings of the molecules in gas and liquid phases.
They also indicate the positions of the atoms' charges in accordance with the rules described in this paper. Each drawing has atoms following the numbers of bonds given in the "specific periodic table for gaseous to liquids transformations" shown in Table 1. Table   Atoms sharing the same cells in the Specific periodic table (Table 1) are isoelectronic atoms, i.e. they have the same electronic configuration. As seen in the table, different elements achieve isoelectronicity thanks to their charging status. For instance, F(+), O(neutral) and N(−) are isoelectronic atoms and positioned in the same cell of Table 1.

Groups in the Periodic
Another particularity is the presence of two groups: organic atoms (green) and inorganic atoms. In each group, atoms show opposite behaviors when their number of electrons increased. As the total number of electrons increases, the inorganic group can gain new covalent bonds whereas the organic group loses its ability to make new bonds. Li, Be and B have 1, 2, 3 bonds respectively, whereas N, O and F have 3, 2, 1 bonds respectively. Table    Carbon shows both behaviors, belonging partly to the inorganic and partly to the organic group. C(+) and C(−) cannot erect more than three bonds whereas C(neutral) has four bonds.  Inorganic atoms can erect most bonds when negatively charged. However, negatively charged inorganic atoms can only connect by using one of their own electron pairs. It cannot accept an electron pair coming from another atom. For instance, BF4(−) cannot become BF5(2−). This is compatible with the limitation of single charged atoms in any compounds.  Organic atoms, on the contrary, can build most bonds when positively charged. This allows a new covalent bond built with an external electron pair. Effectively this is possible, but the number of bonds is automatically decreased by the transfer of a pair in the inner shell. O(+) with 3 bonds can become O (neutral) with two bonds, only when its highest number of bonds is lowered to two. Here again, it might be interesting in the future to determine the physics behind it.

Van der Waals in Chemistry
Chemistry mainly studies atoms' interaction in molecules as being covalent bonds, which involve the sharing of electrons [7]. Covalent bonds involve very strong forces, as in diamond crystals [18], but very local forces, with a range not beyond two involved atoms. There are other non-covalent forces that result from electromagnetic interactions between molecules [19]. Van der Waals forces are classified in this second category. These forces do not result from chemical electronics [20]. They are very weak compared to covalent bonds forces. In the same way, van der Waals' equations are mostly used in molecular physics to give a relation between pressure, temperature and volume [21]. It also predicts transition between vapor and liquid in a macroscopic scale.
As this paper focuses on the formation of new covalent bonds, it seems very difficult to compare both covalent and non-covalent theories.

Association and Dissociation of Molecules
Our previous article [15] focused on molecular dissociation, the disappearance of an electron pair covalently connecting two atoms. The present paper is centered on the reverse process, association, as the creation of a new covalent bond between two atoms. In other words, the bond results from the displacement of an electron pair originating from one of the concerned atoms, to become a bonding pair. Both dissociation and association processes are truly based on one single idea: the movement of an electron pair that is composed of two inseparable electrons.

Conclusion
According to the rules proposed in this paper, gaseous molecules have neutral and/or with single charged atoms. These atoms are only single bonded with surrounded atoms and the number of bonds is indicated by a specific periodic table also proposed in this paper. To form a liquid, a new covalent bond appears. Charges' positions are modified still following the specific periodic table. This article details how electrons' pairs are moved to be compatible with these molecular modifications. By drawing several liquid formations with gaseous molecules, chemical processes are completely explained with electron pairs displacements. The next step might be to use such a process to illustrate ion formations in liquids.