Chemical bonding ionic compounds

Two types of chemical bonds, ionic and covalent, are found in chemical compounds. An ionic bond results from the transfer of valence electrons from the atom of an electropositive element (M) to the atom(s) of an electronegative element (X). It is due to coulombic (electrostatic) attraction between the oppositely charged ions, M (cation) and X (anion). Such ionic bonds are typical of the stable salts formed by combination of the metallic elements (Na, K, Li, Mg, etc.) with the nonmetallic elements (F, Cl, Br, etc.). As an example, the formation of the magnesium chloride molecule from its elemental atoms is shown by the following sequence ... 

In Sections 9-3 and 9-4, we will show you two types of chemical bonds ionic and covalent. It is important to be able to represent compounds in terms of the atoms and valence electrons that make up the chemical species (compounds or polyatomic ions). One of the best ways is to use Lewis symbols and structures. 

The resulting substance is sometimes said to contain an ionic bond. Indeed, the properties of a number of compounds can be adequately explained using the ionic model. But does this mean that there are really two kinds of chemical bonds, ionic and covalent ... 

We have seen that there are two extreme kinds of chemical bonds ionic bonds, formed by the transfer of electrons, and covalent bonds, formed by the sharing of electrons. The physical properties of a compound depend largely upon which kind of bonds hold its atoms together in the molecule. 

When two atoms are joined to make a chemical compound, the force of attraction between the two atoms is the chemical bond. Ionic bonding is characterized by an electron transfer process occurring before bond formation, forming an ion pair. In covalent bonding, electrons are shared between atoms in the bonding process. Polar covalent bonding, like covalent bonding, is based on the concept of electron shar-... 

In Chap. 3 we pointed out that the formulas for both ionic and covalent compounds ignored the nature of the chemical bonds of compounds. A formula is a statement of the combining ratios or the relative numbers of atoms of each kind in the simplest unit representing the composition of the compound. We also learned in Chap. 2 that the atoms of the elements have different masses, which were expressed as relative masses, and that the quantity of any element which is numerically equal to its atomic mass must contain the same number of atoms as the corresponding quantity of any other element. The table of atomic masses assures us that 55.85 g of iron contains the same number of atoms as 12.00 g of the C isotope of carbon. Can we expand the concept of relative mass to compounds as well as elements For example, how many grams of water will contain the same number of fundamental units as 12 g of C carbon We know that the fundamental unit of water is a molecule with the composition H2O. Its relative mass must be equal to the sum of the masses of the atoms in the molecule ... 

The x-ray spectroscopic method for investlgatii the chemical bonding in compounds is free of these limitations. Therefore, there is a continually growing use of x-ray spectra in studies of many aspects of the chemical bonding in solids. One such problem is the determination of the degree of ionicity of bonds (the charge of an element in a compound) from the chemical shifts of the x-ray emission lines. 

The exceptional combination of properties that is a characteristic feature of this class of compounds has its root in the bonding mechanism. The electronic sUiicture calculations reveal that all three main types of chemical bonding (ionic, covalent, and metallic) occur in these substances. 

A is a parameter that can be varied to give the correct amount of ionic character. Another way to view the valence bond picture is that the incorporation of ionic character corrects the overemphasis that the valence bond treatment places on electron correlation. The molecular orbital wavefimction underestimates electron correlation and requires methods such as configuration interaction to correct for it. Although the presence of ionic structures in species such as H2 appears coimterintuitive to many chemists, such species are widely used to explain certain other phenomena such as the ortho/para or meta directing properties of substituted benzene compounds imder electrophilic attack. Moverover, it has been shown that the ionic structures correspond to the deformation of the atomic orbitals when daey are involved in chemical bonds. 

Atoms combine with one another to give compounds having properties different from the atoms they contain The attractive force between atoms m a compound is a chemical bond One type of chemical bond called an ionic bond, is the force of attraction between oppositely charged species (ions) (Figure 1 4) Ions that are positively charged are referred to as cations, those that are negatively charged are anions... 

The chemical structure of a typical divalent metal acetylacetonate, for which the abbreviation would be MCacac). These compounds are internally bonded ionically and complexed to oxygen at the same time. Thus, their intramolecular forces are very strong (they are stable), but their interraolecular forces are weak (they are volatile). 

The basic function of lysis processes is to split molecules to permit further treatment. Hydrolysis is a chemical reaction in which water reacts with another substance. In the reaction, the water molecule is ionized while the other compound is split into ionic groups. Photolysis, another lysis process, breaks chemical bonds by irradiating a chemical with ultraviolet light. Catalysis uses a catalyst to achieve bond cleavage. 

Despite the relatively short history of the chemistry of fluoride compounds, several thousands of binary and ternary fluoride compounds have been described, and their systematization is well developed [39 - 41]. Significant progress was achieved in the study of the crystal chemistry of fluoride compounds thanks to the ionic character of their chemical bonds and corresponding simplicity of their ciystal structure. The structure of these kinds of compounds is defined primarily by the geometry and the energy of mainly... 

On the other hand, fluorine s high electronegativity and its ability to form mostly ionic chemical bonds, provide materials with several useful properties. First, compared to oxides, fluoride compounds have a wide forbidden zone and as a result, have low electroconductivity. In addition, fluorides are characterized by a high transparency in a wide optical range that allows for their application in the manufacturing of electro-optical devices that operate in the UV region [42,43]. 

At the same time, the relatively low energy and ionic character of the chemical bonds between metal and fluorine cause some difficulties in the application of fluoride compounds. First, fluorides typically have a tendency towards thermolysis and hygroscopicity. In addition, fluoride compounds usually display relatively low temperatures of electrostatic and magnetic ordering. 

Needless to say, if ionic character affects the energy stability of a chemical bond it also affects the chemistry of that bond. The tendency toward minimum energy is one of the factors that determine what chemical changes will occur. As a bond becomes stronger, more energy is required to break that bond to form another compound. Hence we see that ionic bonds are favored over covalent bonds and that ionic character in a bond affects its chemistry. 

We shall see in Chapter 2 that the formation of a bond in an ionic compound depends on the removal of one or more electrons from one atom and their transfer to another atom. The energy needed to remove electrons from atoms is therefore of central importance for understanding their chemical properties. The ionization energy, /, is the energy needed to remove an electron from an atom in the gas phase ... 

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