Homoatomic molecules

In a homoatomic bond, i.e. one between two atoms that are the same, the electrons in the covalent bond are shared equally between the two nuclei. This means that there is no permanent charge separation, i.e. one end is not permanently positive, nor the other permanently negative. Suggest two homoatomic molecules formed from elements selected from the first two rows of the Periodic Table. 

While there is no permanent separation of charge in such homoatomic molecules, there may be a temporary separation of the charge present in the covalent bond. The electron density within the molecular orbital is subject to random fluctuations, which result in a temporary separation of charge called the London effect. These fluctuations average to zero over time. 

There is another way in which such temporary charge separation may occur. Suggest what would happen if a homoatomic molecule were brought close to a fixed positive charge. 

For elements which form diatomic molecules A2 with single bonds, Da-a is equal to the energy of dissociation. This applies to H2, the halogens, the alkali metals, silver and copper. A few other elements form homoatomic molecules A . In the P4—AS4—and Sb4-molecules, for instance, each element is bonded to three other atoms, as in compounds of type AB3. As there are six A—A bonds in the A4-molecules, the bond energy Da-a is one sixth of the energy of dissociation for the reaction... 

The topological transition (Fig. 1) from polymeric solids in compounds containing linked polyhedral homoatomic clusters to discrete molecular (soluble) clusters can be conveniently studied by using as examples compounds rich in elements of the main-groups 13 to 15. It is possible for main-group elements in the middle of the periodic table to form homoatomic molecules or ions with localized homonuclear 2c-2e bonds. At higher valence-electron concentrations, fewer bonding and more free-electron pairs are formed. As electron deficiency increases, however, the formation of delocalized bonds becomes necessary, a situation typical of elements on the left of the periodic table. 

Let us begin with energetic properties of polyatomic homoatomic molecules (clusters) of metals (Mn) and nonmetals (An). Because clusters lie somewhere between molecules and bulk solids, approaches and models to study them have come from both sides in most cases, condensed matter theorists have applied solid-state models while quantum chemists have moved from calculations on complex molecules to... 

The three pure substances just mentioned iUustrate three types of molecules found in matter. Oxygen molecules consist of two oxygen atoms, and are called diatomic molecules to indicate that fact. Molecules such as oxygen that contain only one kind of atom are also called homoatomic molecules to indicate that the atoms are all of the same kind. Carbon monoxide molecules also contain two atoms and therefore are diatomic molecules. However, in this case the atoms are not identical, a fact indicated by the term heteroatomic molecule. Carbon dioxide molecules consist of three atoms that are not all identical, so carbon dioxide molecules are described by the terms triatomic and heteroatomic. The words diatomic and triatomic are commonly used to indicate two- or three-atom molecnles, bnt the word polyatomic is usually used to describe molecules that contain more than three atoms. 

It is nsefnl to note a fact here that is discnssed in more detail later in Section 4.11. The smallest particles of some elements and componnds are individual atoms rather than molecules. However, in elements of this type, the individual atoms are all of the same kind, whereas in componnds, two or more kinds of atoms are involved. Thus, the classification of a pure substance as an element or a componnd is based on the fact that only one kind of atom is fonnd in elements and two or more kinds are found in compounds. In both cases, the atoms may be present individnally or in the form of homoatomic molecules (elements) or heteroatomic molecules (compounds). Some common household materials are pure substances (elements or componnds), snch as alnminnm foil, baking soda, and table salt. 

Homoatomic molecules or individual atoms of the same kind... 

Oxygen gas and solid sulfur are both made up of homoatomic molecules. The two react to form a single substance, sulfur dioxide. Use the term homoatomic or heteroatomic to classify molecules of sulfur dioxide. Explain your reasoning. 

This makes LiH difficult to observe as a diatomic molecule because it is unstable with respect to homoatomic molecules of its constituent elements. 

A bond between two different atoms cannot be purely covalent. Depending on the electronegativity of the bonded atoms, the bonded electron pair shifts toward one of the atoms. A vector showing the magnitude and direction of the shifting of this electron pair is known as a bond moment. In polyatomic molecules, each bond has an individual bond moment. The dipole moment ) of a molecule is the vectorial addition of such bond moments. In the cases where all the individual bond moments are zero (homoatomic molecules), the resultant dipole moment is always zero. However, the converse is not true. Because of equal and opposite values of individual bond moments, some molecules show a zero net dipole moment. As applied to coordination compounds, a dipole measurement can be of value in distinguishing between isomers of a compound, particularly between cis- and trans- isomers. A trans- isomer exhibits a low or zero dipole moment. 

As noted by Pauling, the dissociation energies of the heteroatomic molecules, AB, all exceeded the arithmetic mean of the dissociation energies of the two corresponding homoatomic molecules AA and BB ... 

All other homoatomic Pn cluster anions are cage molecules with localized two-center-two-electron bonds. The cyclic [PnJ anion has been characterized by NMR spectroscopy for Pn = P [210], and structures are known for Pn = P, As, Sb, Bi (Table 2). A planar [Ps] anion has only been detected in solution by P NMR spectroscopy [210]. Envelop-shaped five- and six-membered rings are found for [Pns] and [Pe]", whereas [Asg]" deviates only slightly from planarity and has a chair conformation. The aromaticity of the planar anions [P4] and [Pe]" is distinct from that of regular 671-aromatic hydrocarbons and has been described... 

However, the two major branches of chemistry are still studied separately. This is because there is a useful distinction to be drawn between the two. Yet, this distinction is no longer based on the presence or absence of a vital force, but rather is partly derived from the practical consequences of the stability of the homoatomic carbon/carbon bond. One such consequence is that the chemistry of carbon-containing compounds often involves the study of molecules that contain many such bonds. Thus, because of the multitude and variety of these compounds, it is convenient to study them separately. In contrast, inorganic chemistry is often concerned with the structure and utility of molecules that contain heteroatomic bonds, either ionic or covalent. This means that in an inorganic molecule, there are often two or more elements that could be said to be of equal prominence. In addition, there still remains the point that carbon compounds form the vast majority of the constituent components of living beings, while non-carbon compounds comprise the environment in which those beings exist. So the distinction is the same, but the justification is different. 

In a homoatomic bond, such as between two fluorine atoms, there is no permanent charge separation. If the bond in the fluorine molecule should break, what do you think would be the likely products Write an equation for your suggested answer. 

Secondly, a triply bonded dinitrogen molecule, in which each nitrogen has an oxidation of zero, bonds to the atomic nitrogen anion to give rise to one of the canonical structures of the azide anion, namely, one terminal nitrogen has one lone pair and three homoatomic bonds, and so has an oxidation number of zero. The central atom has four homoatomic bonds, but one of which is polarised away from it, i.e. the dative bond, and so it has an oxidation number of+1. The other terminal nitrogen started with one extra electron and now also has a homoatomic bond, which is polarised towards it, and so now has an oxidation number of-2. This nitrogen atom has three lone pairs. 

Table IX Names of homoatomic, binary and certain other simple molecules, ions, compounds, radicals and substituent groups...

Very recently, high-level ab initio MO calculations on various isomers of homoatomic sulfur molecules S with n=2-10 have been carried out [53]. The results are given in Table 5. As can be seen, these computed data agree rather well with the experimental data by Rau et al. [24] shown in Table 1, with the exception of S5. This molecule is hkely to undergo pseudorotation in the vapor phase resulting in an enhanced molecular entropy which is not taken into account in ab initio calculations. Furthermore, since S5 is a minority species in sulfur vapor at all temperatures and pressures, it is possible that the data by Rau et al. are somewhat unreliable as far as this molecule is concerned. 

Elemental Sulfur Molecules and Ions. Rheingold, A. L., Ed. "Homoatomic Rings, Chains and Macromolecules of Main Group Elements" Elsevier, Amsterdam, 1977 page 477. 

The occurrence of homoatomic anions [En] of the elements of groups IV (C, Si, Ge, Sn, Pb) and V (P, As, Sb, Bi) as constituents of Zintl phases is well knownJ Despite numerous attempts, just a few of the En clusters have been isolated as uncharged molecules E Rx from the Zintl phases by reaction with suitable agents such as alkyl chlorides. 

Use the terms diatomic, triatomic, polyatomic, homoatomic, or heteroatomic to classify the following molecules correctly ... 

Earlier, we looked at three examples of pure substances—oxygen, carbon monoxide, and carbon dioxide—and found that the molecules of these substances are of different types. Oxygen molecules are diatomic and homoatomic, carbon monoxide molecules are... 

Scientific models are explanations for observed behavior. The results of many observations led scientists to a model for matter in which all matter is composed of tiny particles. In many substances, these particles are called molecules, and they represent the smallest piece of such substances that is capable of a stable existence. Molecules, in turn, are made up of atoms, which represent the limit of chemical subdivision for matter. The terms diatomic, triatomic, polyatomic, homoatomic, and heteroatomic are commonly used to describe the atomic composition of molecules. 

---