Bond Energy

(noun)

A measure of a chemical bond's strength. It is experimentally determined by measuring the heat (or enthalpy) required to break a mole of molecules into their constituent individual atoms.

Related Terms

Examples of Bond Energy in the following topics:

  • Bond Energy

    • Bond energy is the energy required to break a covalent bond homolytically (into neutral fragments).
    • Bond energies are commonly given in units of kcal/mol or kJ/mol, and are generally called bond dissociation energies when given for specific bonds, or average bond energies when summarized for a given type of bond over many kinds of compounds.
    • Tables of bond energies may be found in most text books and handbooks.
    • The following table is a collection of average bond energies for a variety of common bonds.
    • Such average values are often referred to as standard bond energies, and are given here in units of kcal/mole.

  • Bond Energy

    • Bond energy is the measure of bond strength.
    • Bond energy is a measure of a chemical bond's strength, meaning that it tells us how likely a pair of atoms is to remain bonded in the presence of energy perturbations.
    • These energy values (493 and 424 kJ/mol) required to break successive O-H bonds in the water molecule are called 'bond dissociation energies,' and they are different from the bond energy.
    • The bond energy is the average of the bond dissociation energies in a molecule.
    • Identify the relationship between bond energy and strength of chemical bonds

  • Bond Enthalpy

    • Bond enthalpy, also known as bond dissociation energy, is defined as the standard enthalpy change when a bond is cleaved by homolysis, with reactants and products of the homolysis reaction at 0 K (absolute zero).
    • For instance, the bond enthalpy, or bond-dissociation energy, for one of the C-H bonds in ethane (C2H6) is defined by the process:
    • Each bond in a molecule has its own bond dissociation energy, so a molecule with four bonds will require more energy to break the bonds than a molecule with one bond.
    • As each successive bond is broken, the bond dissociation energy required for the other bonds changes slightly.
    • Bond dissociation energies for different element pairings are listed.

  • Energy Changes in Chemical Reactions

    • Due to the absorption of energy when chemical bonds are broken, and the release of energy when chemical bonds are formed, chemical reactions almost always involve a change in energy between products and reactants.
    • By the Law of Conservation of Energy, however, we know that the total energy of a system must remain unchanged, and that oftentimes a chemical reaction will absorb or release energy in the form of heat, light, or both.
    • The energy change in a chemical reaction is due to the difference in the amounts of stored chemical energy between the products and the reactants.
    • This means that the energy required to break the bonds in the reactants is less than the energy released when new bonds form in the products.
    • This means that the energy required to break the bonds in the reactants is more than the energy released when new bonds form in the products; in other words, the reaction requires energy to proceed.

  • Bonding and Antibonding Molecular Orbitals

    • MO modeling is only valid when the atomic orbitals have comparable energy; when the energies differ greatly, the bonding mode becomes ionic.
    • This MO is called the bonding orbital, and its energy is lower than that of the original atomic orbitals.
    • The reduction these electrons' energy is the driving force for chemical bond formation.
    • Whenever symmetry or energy make mixing an atomic orbital impossible, a non-bonding MO is created; often quite similar to and with energy levels equal or close to its constituent AO, the non-bonding MO creates an unfavorable energy event.
    • Bonding and antibonding levels in the hydrogen molecule; the two electrons in the hydrogen atoms occupy a bonding orbital that is lower in energy than the two separate electrons, making this an energy-favorable event.

  • Types of Energy

    • The various types of energy include kinetic, potential, and chemical energy.
    • Energy associated with objects in motion is called kinetic energy.
    • On a chemical level, the bonds that hold the atoms of molecules together have potential energy.
    • When gas ignites in the engine, the bonds within its molecules are broken, and the energy released is used to drive the pistons.
    • The potential energy stored within chemical bonds can be harnessed to perform work for biological processes.

  • Bond Order

    • Bond order is the number of chemical bonds between a pair of atoms.
    • Bond order indicates the stability of a bond.
    • Bond order is also an index of bond strength, and it is used extensively in valence bond theory.
    • In the second diagram, one of the bonding electrons in H2 is "promoted" by adding energy and placing it in the antibonding level.
    • By adding energy to an electon and pushing it to the antibonding orbital, this H2 molecule's bond order is zero, effectively showing a broken bond.

  • Double and Triple Covalent Bonds

    • The newly formed hybrid orbitals all have the same energy and have a specific geometrical arrangement in space that agrees with the observed bonding geometry in molecules.
    • Covalent bonds can be classified in terms of the amount of energy that is required to break them.
    • Based on the experimental observation that more energy is needed to break a bond between two oxygen atoms in O2 than two hydrogen atoms in H2, we infer that the oxygen atoms are more tightly bound together.
    • Therefore, it would take more energy to break the triple bond in N2 compared to the double bond in O2.
    • Double bonds have shorter distances than single bonds, and triple bonds are shorter than double bonds.

  • Single Covalent Bonds

    • Single covalent bonds are sigma bonds, which occur when one pair of electrons is shared between atoms.
    • There are four hierarchical levels that describe the position and energy of the electrons an atom has.
    • Principal energy levels are made out of sublevels, which are in turn made out of orbitals, in which electrons are found.
    • The strongest type of covalent bonds are sigma bonds, which are formed by the direct overlap of orbitals from each of the two bonded atoms.
    • A single covalent bond can be represented by a single line between the two atoms.

  • Bond Lengths

    • The bond length is the average distance between the nuclei of two bonded atoms in a molecule.
    • This is because a chemical bond is not a static structure, but the two atoms actually vibrate due to thermal energy available in the surroundings at any non-zero Kelvin temperature.
    • Atoms with multiple bonds between them have shorter bond lengths than singly bonded ones; this is a major criterion for experimentally determining the multiplicity of a bond.
    • The potential energy function for this system is also indicated.
    • The minimum energy occurs at the equilibrium distance r0, which is where the bond length is measured.