Define the following terms, and give an example for each: Lewis dot symbol, ioni

Question

Define the following terms, and give an example for each: Lewis dot symbol, ionic bond. Coulomb's law, Borm-Haber cycle, covalent bond. Iewis structure, octet rule. What is the basis for assigning oxidation numbers of elements in their compounds9 Why is it said that electronegativity is a relative concept? 4. Outline the steps used to write a Lewis structure. Give an example in your answer Explain what is meant by an atom's formal charge Use an example in your answer Define the term resonance as used in Lewis structures. Name three exceptions to the octet rule, and give an example for each.

Explanation / Answer

Lewis Symbols are simplified Bohr diagrams displaying electrons in the outermost energy level. A Lewis Symbol for an element is composed of a chemical symbol surrounded by dots that are used to represent valence electrons. The example of a Lewis symbol is explained below with the element Carbon, which has the electron configuration of 1s22s22p2. This Lewis symbol shows that carbon has four valence electrons in its outer orbital.

:C:

Ionic bonding is the complete transfer of valence electrons between atoms. In ionic bonds, the metal loses electrons to become a positively charged cation, whereas the nonmetal accepts those electrons to become a negatively charged anion. Ionic bonds require an electron donor, often a metal, and an electron acceptor, a nonmetal. By losing the electrons, the metals can achieve noble gas configuration and satisfy the octet rule. Similarly, nonmetals that have close to 8 electrons in their valence shells tend to readily accept electrons to achieve noble gas configuration. The charges on the anion and cation correspond to the number of electrons donated or received. In ionic bonds, the net charge of the compound must be zero. For E.g The bond between Na and Cl to form NaCl.

The term covalent bond is used to describe the bonds in compounds that result from the sharing of one or more pairs of electrons. Covalent bonding includes many kinds of interactions, including -bonding, -bonding etc. For eg. Bonding in CH4 molecule.

Coulomb's law states that the electrical force between two charged objects is directly proportional to the product of the quantity of charge on the objects and inversely proportional to the square of the separation distance between the two objects. In equation form, Coulomb's law can be stated as:

F=k*Q1*Q2/d2

where Q1 = the quantity of charge on object 1

Q2 = the quantity of charge on object 2

d = the distance of separation between the two objects

The symbol k is a proportionality constant known as the Coulomb's law constant.

The Coulomb's law equation provides an accurate description of the force between two objects whenever the objects act as point charges.

Born Haber cycle is a method developed by Max Born and Fritz Haber to correlate the lattice energies of ionic solids to other thermodynamic data like like ionization energy, electron affinity, dissociation energy, sublimation energy and heat of formation. Lattice enthalpy is defined as enthalpy change which occurs when one mole of ionic solid is formed by close packing of constituent ions in gaseous state. Born Haber cycle is based on Hess law which states that the standard enthalpy change of reactions is the sum of algebraic sum of the standard enthalpies of reactions into which the overall reaction may be divided.

For example, the formation of sodium chloride from sodium and chloride ion involves 788 kj/mol of energy and dissociation of sodium chloride into it constituent ions requires same amount of energy.

NaCl(s) Na+(g) + Cl- (g) H°= 788 kj/mol

Na+(g) + Cl-(g) NaCl(s) H° = -788 kj/mol

Octet Rule:

The octet rule states that elements gain or lose electrons to attain an electron configuration of the nearest noble gas. Atoms follow the octet rule because they always seek the most stable electron configuration. Following the octet rule, results in completely filled s- and p- orbitals of an atom outermost energy level, therefore making them more stable.

Exceptions:

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