What are Chemical Bonds? We do not have a simple or even a complete definition, but it is best described by Steven and Susan Zumdahl as “the force or, more accurately, the the energy, that holds two atoms together in a compound.” (56). What this means, is that to form a compound (two or more elements fixed together in a mixed proportion) there must be some sort of force or energy that keeps these elements joined in a mixture. These forces/energies are chemical bonds. The concept of the nature of chemical bonding came to fruition during the early 20th century.
Due to John Dalton’s discovery of the electron (e-). This discovery enabled American Chemist, Gilbert N. Lewis to explain his theory of the valence shell of electrons, with his Electron-Dot Structures (Lewis Dot Structures) in 1902 and his theory of bonding, specifically covalent bonding, in 1916. Chemical Bonding has three main subsets: Covalent Bonds, Ionic Bonds, and Hydrogen Bonds. These different subsets of bonds all have different properties which stem from “the basic concept that the stability of the noble gas family (Group VIIIA or Group 18) drives the concept of bonding” (Langley and Moore 144).
The first main subset of chemical bonding is the Covalent Bond. A Covalent bond is best described as a bond in which one or more electron pairs are shared between multiple atoms. An example of a covalent bond is Methane (CH4, Fig. 1). Covalent chemical bonds involve the sharing of valence electrons pairs between two atoms. A covalent bond is the most stable and on average, the strongest bond among the four binding subsets, due to the bonds having a full valence electron shell according to the octet rule of chemistry. The octet rule states that during chemical reactions, atoms lose, gain, or share electrons in order to achieve a filled valence shell of eight electrons. There is also a specific subset of covalent bonds called Polar Covalent Bonds.
These are covalent bonds in which the sharing of the electron pair is unequal. Within these bonds there is a charge separation with one atom being slightly more positive and the other more negative, this leads to the bond producing a dipole moment. A dipole moment is best described as the mathematical product of the separation of the ends of a dipole (a molecule in which a concentration of positive electric charge is separated from a concentration of negative charge) and the magnitude of the charges.Fig. 1. “Methane Lewis Dot Structure”The second main subset of Chemical Bonding is the Ionic bond. An ionic bond according to Langley and Moore, “results from the transfer of electrons from a metal to a nonmetal” (145). The transferring of electrons in ionic bonds occurs due to the formation of cations and anions.
A cation is a positively charged ion while an anion is a negatively charged ion. An ion is a particle having a non-zero net electrical charge, or more simply is an atom or molecule whose total number of electrons is not equal to its total number of protons. Normally the metal in will lose an electron during bonding which causes the metal to become the cation. While on the reverse side the nonmetal will accept the electron from the metal, this causes the nonmetal to become an anion. The number of electron lost or gained is determined by the octet rule, which is mentioned above. Ionic bonds are on average, the second strongest bonds that are currently known to exist just behind covalent bonds (this does vary based on which compounds but generally they are the strongest). The most common example of an ionic bond is Sodium Chloride, or table salt (Fig.
2). In this example, Sodium loses one electron to form a cation (Na+) and Chlorine gains an electron to become an anion of Chloride (Cl-).Fig. 2 “Ionic Bonding of Na and Cl”The third major subset of bonding is the Hydrogen Bond.
A Hydrogen bond is described as “unusually strong dipole-dipole attractions that occur among molecules in which Hydrogen is bonded to a highly electronegative atom” (Steven and Susan Zumdahl A34). A Hydrogen Bond isn’t really a bond at all. “It is a force of attraction between a hydrogen atom in one molecule and a small atom of high electronegativity (chemical property that describes the tendency of an atom to attract electrons towards itself) in another molecule” (hyperphysics.edu). Hydrogen Bonds are intermolecular forces, not intramolecular force as the other “bond” subsets are. The Hydrogen Bond is one of the weakest bonds having only roughly 5-10% of the strength of a covalent bond.
“Hydrogen bonding has a very important effect on the properties of water and ice” (Langley and Moore 164). Hydrogen bonding gives the explanations into why Hydrofluoric Acid (HF)(aq) is a weak acid while Hydrochloric Acid (HCl)(aq) is a strong acid. To explain this it’s as simple the bond between the HF atoms traps the hydrogen atoms which makes it much harder to release and H+ ion (Fig. 3) This hydrogen bond in turn is strong enough to make the acid weak.Fig. 3 “Hydrofluoric Acid by way of Hydrogen Bonding traps the H+ ion”Chemical bonding is possibly the most basic and fundamental concept of Chemistry, it is the building block of advanced knowledge in compounds, solutions, and equations. To progress through the ranks of Chemistry as an area of study you must familiarize yourself with the subsets of Chemical Bonding.
Covalent Bonds, Hydrogen Bonds, and Ionic Bonds make up the entire world in which we live in, without these bonds there is no us. The differences between the subsets are major but also simple to differentiate. Once you understand these differences you will understand the world on the atomic scale.