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.
- 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
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
Features of Covalent Bonds
- Covalent bonds form single, double and triple bonds