Theory of Chemical Bonding, Chemistry tutorial

Theory of Chemical Bonding

When 2 atoms of similar or different elements approach each other, the energy of the combination of the atoms becomes less than the sum of the energies of the 2 divide atoms at a huge distance. We say that the 2 atoms have joined or a bond is formed among the two. The bond is termed a chemical bond. Therefore a chemical bond might be visualized as a consequence that leads to reduce in the energy. The mixture of atoms leads to the formation of a molecule that has distinct properties different from that of the constituent atoms.

A question arises, 'How do atoms attain reduce in energy to form the bond'. The answer lies in the electronic configuration. As we are aware, the noble gases don't react through other components to form compounds. This is due to their steady electronic configuration through 8 electrons (two in case of helium) in their outermost shells. The shape of a bond between two atoms might be visualized in terms of their acquiring steady electronic configurations. That is when 2 atoms (other than that of noble gases) join they will do so in these a way that they accomplish an electronic configuration of the nearest noble gas. The constant electronic configuration of the noble gases can be attained in a number of ways; via losing, expanding or sharing of electrons. Consequently, there are dissimilar kinds of chemical bonds, as,

  • Ionic or electrovalent bond
  • Covalent bond
  • Co-ordinate covalent bond

In addition to such we have a special kind of bond termed hydrogen bond. Let us converse about dissimilar kinds of bonds, their formation and the properties of the compounds so shaped.

The term 'chemical affinity' termed more to the ability to react (undergo a chemical transform) than to form a steady compound. When it was realized that chemical compounds were shaped of discrete molecules enclosing fixed numbers of atoms, require to clarify molecular stability extended, leading to the notion of the interatomic chemical bond (Latin inter for among plus band for a fastening) holding atoms mutually. Early Nineteenth Century speculations about the origin of interatomic bonds were influenced through contemporary discoveries in electricity, representative that 'opposites' attract. Positive and negative charges are electrical opposites, and north and south poles are attractive opposites. Accurately just what constituted chemical opposite wasn't clear, however. Chemists had classified materials into metals and non-metals, and into acids and bases, both of that seemed conflicting in the sense that they had 'affinity' for each other and readily reacted mutually to form new compounds. Yet there was not little evidence to support the hypothesis of Avogadro that non-metal gases were composed of 2 atoms of the similar element, nor were there any clarifications for the solid state of metallic elements, or the extreme hardness of non-metallic elements these as diamond.

The number of bonds a component could make, termed the valence (Latin valere for strength) of the element, is suggested through the atom ratios of chemical formulas, and ordinarily bounded to a little number. For instance, hydrogen atoms never form bonds to more than one an additional atom, so are assigned a valency of one. Oxygen has a valency of 2(is divalent) as each oxygen atom joins through 2 hydrogen atoms in forming water (H2O, more descriptively written showing atom connections as H-O-H). Carbon has a valency of 4 (is tetravalent) since it joins by a maximum of four hydrogen atoms (in methane, CH4 more descriptively shown through C encircled by 4 H), or, equivalently, maximum of two oxygen atoms, each by a valency of two (in carbon dioxide, CO2, more descriptively written O-C-O).

Ionic and Covalent Chemical Bonds

Chemical salts are found to conduct electricity when melted or dissolved in water, suggesting the presence of charge carriers, called ions (from the Greek for traveler). Since salts are neutral compounds, the charge carriers must be separated into 2 groups, one positively charged and the other negatively charged. The oppositely charged ions would be bound through electrostatic attractions, or ionic bonds. Since chemical salts are recognized to be composed of metallic components bound to non-metallic elements, the most reactive of that are establish at opposite ends of the periodic table, ionic attraction can be described in terms of the attraction of opposites.

When metals or nonmetals bond to elements of their own type, the cause for the bonding isn't so clear. Compounds enclosing dissimilar elements might have several attractions due to the dissimilarities between the elements, but homonuclear (one-element) polyatomic (more than one atom) elements these as H2 or sodium metals are leap through some common feature rather than by some difference between the atoms. Such bonds, termed covalent bonds (Latin co + valere for joint strength), aren't bounded to homonuclear molecules but as well take place between atoms of different components that are close in behavior. The periodic table summarizes the properties of the components, as well as bonding trends also, and can be utilized to decide the essential kind.

The Electronic Theory of Chemical Bonding

Nowadays it is identified that the chemical bond is the most essential and vital characteristic of molecules. Understanding the properties of the interatomic bonds in molecules is important to understanding the physical structure and chemical reactivities of molecular matter. Chemical bonds effect from the electrostatic (Coulombic) interactions of the electrons and nuclei of atoms. Fundamentally, the outer-shell electrons on each atom in a molecule can be thought to be magnetized to the nuclei of adjacent atoms in addition to their own nuclei. Fig diagrams the electrostatic interactions for a classical particle model of the dihydrogen molecule, the simplest neutral polyatomic molecule. In fact this model, even though helpful, is an oversimplification on numerous counts; as was found for atoms, electrons in the presence of nuclei don't perform as particles and standard models fall short of precise descriptions of electronic structure.

555_Electrostatic Interactions in Dihydrogen.jpg

Fig:  Electrostatic Interactions in Dihydrogen

The wave mechanical form of electronic formation is the suitable explanation for multiple electron systems, and applies to molecules in addition to atoms (cf. Section on Wave Mechanics and Section on Periodic Electronic Configurations). The nature of the chemical bond is revealed in the solutions to Schrödinger's equation for molecules. As in the case of atoms, precise solutions attained for easy molecules are utilized to justify established linking heuristics, as well as produce new molecular linking principles.

A main characteristic that emerges in investigating chemical bonds through wave mechanics is electrons prefer to be paired. This fact clarifies the stability of the simplest neutral molecule, H2(through 2 paired electrons) through respect to H atoms, in addition to the instability of He2 by respect to He atoms (each having 2 paired electrons). The stability of paired electrons and filled subshell electronic configurations prove to be most helpful common principles for explaining a variety of characteristics of molecules.

Before delving additional into the nature of the chemical bond as elucidated via the wave mechanics, we will discover an extensively utilized powerful pre-wave mechanical linking heuristic discovered via G. N. Lewis early in the starting of the Twentieth Century. Lewis considered electrons to be standard particles that he symbolized graphically via dots. Pairs of electrons between atoms he symbolized by lines to signify bonds connecting the atoms mutually.

Lewis's contribution consisted of a easy process of counting the dots to forecast chemical formulas, molecular geometry, and diverse chemical properties.

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