Understanding Chemical Bonds: Covalent, Ionic, and Metallic
Covalent bonds: A covalent bond is formed when two atoms share electron pairs, allowing the atoms to achieve an external configuration that satisfies the “Octet Rule”: 8 (eight) or 2 (two) electrons.
Types of Covalent Bonds
Covalent bond – common: A shared electron pair is formed by one electron from each of the atoms involved. This bond can occur between two similar atoms, resulting in a nonpolar covalent bond, or between different atoms, resulting in a polar covalent bond.
- Nonpolar Covalent Bond: In a nonpolar covalent bond, such as that formed between two chlorine atoms, the electrons are located according to their geometric distribution.
- Polar Covalent Bond: In a polar covalent bond, electrons are not attracted equally by the nuclei and statistically spend more time near the nucleus of the more electronegative atom. This difference in attraction generates a permanent dipole in the molecule. Atoms may share one or more pairs of electrons, resulting in single, double, or triple covalent bonds.
- Dative Covalent Bond (Coordinated): This bond occurs between two atoms of two elements, where the shared electron pair is contributed by only one of the two atoms.
Ionic Bonds
Ionic bonds, unlike covalent bonds, are not formed by sharing electrons. Instead, they are formed by the electrostatic force that holds together the ions that form compounds.
In the case of an anion or cation, the loss or gain of electrons leads to a noble gas electron structure, according to the Octet Rule. Atoms with low ionization energy form cations, and atoms with high ionization energy form anions.
The ionic bond involves all the ions in the compound. Unlike covalent compounds, the ionic bond does not form localized unions, which is why they are indistinguishable molecules.
Metallic Bonds
Metallic bonds are chemical bonds found between metal atoms.
Metals form a lattice where the “nodes” are formed by the cations. The bonding electrons are delocalized, moving between cations in different directions. This creates a structure of positive ions that appear to be immersed in a “sea of electrons.” The cohesive forces between these cations and delocalized electrons form a bond between atoms called metallic bonding.
Key Differences in Bonding
- Ionic Bonding: Involves the transfer of electrons from a metal, forming cations and anions, which are held together by electrostatic forces. This type of bonding occurs between atoms of a metal and a nonmetal.
- Covalent Bonding: Occurs between molecules formed by atoms of nonmetals. In this bond, the atoms share one or more pairs of electrons to complete the octet. Within this type of bond, there are polar and nonpolar molecules.
In the case of simple gases (H2, N2, O2, F2, and Cl2), the atoms that form the molecules are equal, and the nuclei are drawn with equal intensity to share the electron pair, so the distribution of electric charges is uniform. The molecules have no electric charges (poles) and are called nonpolar.
Covalent Coordination: Occurs when the shared electron pair is contributed by one of the atoms. The atom that gives the pair of electrons is called the donor, and the atom that accepts the share is called the acceptor.
Metal Union: Exists between metal atoms, i.e., elements of low electronegativity. The few outer electrons are attracted by the atomic nuclei and therefore remain relatively free from the network of metal cations. Therefore, the electrons involved in this union do not belong to any particular volume, but the entire crystal structure is very compact.