Covalent Bond

Yeshwini & Xavi

History of Covalent Bond

  • The person who is largely credited for his development in the “dot and cross’ model of bonding was an American called Gilbert Newton Lewis(1875-1946).
  • He initially used the cube structure to represent in the electrons in an atom.
  • Later due to flaws in this, came up with the “dot and cross” model to represent electrons in an atom, where electrons revolve around concentric circles.

Cube Model

  • visualized the outer shell of an atom as a cube with electrons at each vertex.
  • Inner shells of electrons were smaller cubes inside.
  • He knew that in a stable atom or molecule (except hydrogen) that there must be eight electrons around each atom. (8 corners of a cube)

Example of Bonds formed in the Cubic Model

Weaknesses of the Cube model

  • As the atomic number gets bigger the representation of the electrons around the atom was not clear.

  • not very comprehensive and practical to explain the atom

  • statements from bohr atomic theory did not match his analysis of electrons put in a cubic structure

WHAT IS COVALENT BONDING? A covalent bond is when atoms share electrons with each other in order to attain a noble gas electron configuration

Features of Covalent Bonding

  • Where ---occurs between nonmetals

  • Why--

  • If atoms have similar electronegativities*(same affinity to electrons), covalent bonds occur.

  • both atoms have the same affinity for electrons and neither has a tendency to donate them, they share the electrons to achieve octet configuration.

  • The ionization energy of the atom is too large and the electron affinity of the atom is too small for ionic bonding to occur.

Ex- Carbon does not form ionic bonds because it has 4 valence electrons, half of an octet. To form ionic bonds, Carbon molecules must either gain or lose 4 electrons. This is highly unfavorable; therefore, carbon molecules share their 4 valence electrons through single, double, and triple bonds so that each atom can achieve noble gas configurations.

Electronegativity: Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. Fluorine has the highest electronegative element.

Features of Covalent Bond

  • The atoms hold atoms together by the forces of attraction between the electron pair(bonding pair) and the two nuclei.

  • The electrostatic force between the two nuclei

    (positive charge) and the shared electrons in the

    middle(negative charge) bring the two atoms

    tightly together.

Features of Covalent Bonds

  • Covalent bonds form single, double and triple bonds