chemical bond

Examples of chemical bond in the following topics:

• Introduction to Bonding

  • Chemical bonding describes a variety of interactions that hold atoms together in chemical compounds.
  • Chemical bonds are the connections between atoms in a molecule.
  • Chemical bonds are the forces of attraction that tie atoms together.
  • This pictures shows examples of chemical bonding using Lewis dot notation.
  • Bonds, especially covalent bonds, are often represented as lines between bonded atoms.

• Hybridization in Molecules Containing Double and Triple Bonds

  • sp2, sp hybridizations, and pi-bonding can be used to describe the chemical bonding in molecules with double and triple bonds.
  • Ethene (C2H4) has a double bond between the carbons.
  • sp hybridization explains the chemical bonding in compounds with triple bonds, such as alkynes; in this model, the 2s orbital mixes with only one of the three p-orbitals, resulting in two sp orbitals and two remaining p-orbitals.
  • The chemical bonding in acetylene (ethyne) (C2H2) consists of sp-sp overlap between the two carbon atoms forming a sigma bond, as well as two additional pi bonds formed by p-p overlap.
  • In ethene, carbon sp2 hybridizes, because one π (pi) bond is required for the double bond between the carbons, and only three σ bonds form per carbon atom.

• Bond Order

  • Bond order is the number of chemical bonds between a pair of atoms.
  • Bond order is the number of chemical bonds between a pair of atoms; in diatomic nitrogen (N≡N) for example, the bond order is 3, while in acetylene (H−C≡C−H), the bond order between the two carbon atoms is 3 and the C−H bond order is 1.
  • 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.
  • For a bond to be stable, the bond order must be a positive value.

• 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.
  • 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.
  • Describe the types of energy changes that can occur in chemical reactions

• 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.
  • Bonds involving hydrogen can be quite short; the shortest bond of all, H–H, is only 74 pm.
  • 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.
  • For example, the bond length of $C - C$ is 154 pm; the bond length of $C = C$ is 133 pm; and finally, the bond length of $C \equiv C$ is 120 pm.

• Bonding in Coordination Compounds: Valence Bond Theory

  • Valence bond theory is used to explain covalent bond formation in many molecules.
  • Valence bond theory is a synthesis of early understandings of how chemical bonds form.
  • Lewis proposed that the basis of chemical bonding is in the ability of atoms to share two bonding electrons.
  • Where bond order is concerned, single bonds are considered to be one sigma bond, double bonds are considered to contain one sigma and one pi bond, and triple bonds consist of one sigma bond and two pi bonds.
  • Valence bond theory is used to explain covalent bond formation in many molecules, as it operates under the condition of maximum overlap, which leads to the formation of the strongest possible bonds.

• Bond Polarity

  • Bond polarity exists when two bonded atoms unequally share electrons, resulting in a negative and a positive end.
  • In chemistry, bond polarity is the separation of electric charge along a bond, leading to a molecule or its chemical groups having an electric dipole or dipole moment.
  • Electrons are not always shared equally between two bonding atoms.
  • A completely polar bond, or ionic bond, occurs when the difference between electronegativity values is large enough that one atom actually takes an electron from the other.
  • The terms "polar" and "nonpolar" usually refer to covalent bonds.

• Bond Enthalpy

  • Bond enthalpy is defined as the enthalpy change when a covalent bond is cleaved by homolysis.
  • Enthalpy is a measure of the total heat energy content in a thermodynamic system, and it is practically used to describe energy transfer during chemical or physical processes in which the pressure remains constant.
  • 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.

• Hydrogen Bonding

  • A hydrogen bond is a type of dipole-dipole interaction; it is not a true chemical bond.
  • This hydrogen atom is a hydrogen bond donor.
  • Greater electronegativity of the hydrogen bond acceptor will create a stronger hydrogen bond.
  • Hydrogen bonds are shown with dotted lines.
  • Where do hydrogen bonds form?

• Ionic vs Covalent Bond Character

  • Chemical compounds are frequently classified by the bonds between constituent atoms.
  • The bond formed between any two atoms is not a purely ionic bond.
  • Bonds that fall in between the two extremes, having both ionic and covalent character, are classified as polar covalent bonds.
  • This bond is considered to have characteristics of both covalent and ionic bonds.
  • Discuss the idea that, in nature, bonds exhibit characteristics of both ionic and covalent bonds