Covalent Bonds

Covalent bonding occurs when atoms share electrons to complete their outer electron shells. This bond is typically formed between nonmetal atoms. In a covalent bond, the shared electrons are localized between the bonded atoms. This type of bonding is common in molecular compounds.

Let’s say two friends, Alice and Bob, decide to form a strong bond by holding the rope together. They both contribute their strength equally, sharing the load of the rope. In this case, Alice and Bob represent atoms sharing electrons in a covalent bond.

Molecules and Covalent bonds

Covalent bonds are formed when two atoms share pairs of electrons, allowing both atoms to achieve a more stable electronic configuration, often resembling the noble gas configuration. Here’s a description of the formation of single covalent bonds in several molecule.

Here is a concise table summarizing the electron sharing in some simple covalent molecules:

H2 (Hydrogen Gas):

• In a hydrogen molecule (H2), two hydrogen (H) atoms come together to share one electron pair. Each hydrogen atom has only one electron in its 1s orbital. When they share their electrons, both hydrogen atoms end up with two electrons each, achieving the electron configuration of helium (He). Helium has two electrons and a full 1s orbital, making it stable.

Cl2 (Chlorine Gas):

• In a chlorine molecule (Cl2), two chlorine (Cl) atoms share one electron pair. Chlorine has 17 electrons in its ground state, and it needs one more electron to achieve the electron configuration of argon (Ar) which is stable with 18 electrons and a full 3p orbital. By sharing one electron pair, each chlorine atom completes its outer electron shell and achieves stability.

H2O (Water):

Water (H2O) consists of one oxygen (O) atom sharing two electron pairs with two hydrogen (H) atoms. Oxygen has 8 electrons in its ground state and needs two more electrons to achieve the electron configuration of neon (Ne) which is stable with 10 electrons and a full 2p orbital. Each hydrogen atom shares one electron pair with the oxygen atom, providing the oxygen atom the additional two electrons it needs to complete its outer shell. The result is that oxygen now has 8 electrons (like neon), and each hydrogen has 2 electrons.

CH4 (Methane):

• Methane (CH4) is composed of one carbon (C) atom sharing one electron pair with each of the four hydrogen (H) atoms. Carbon has 6 electrons in its ground state and needs four more electrons to achieve the electron configuration of neon (Ne), which is stable with 10 electrons and a full 2p orbital. By sharing one electron pair with each hydrogen atom, carbon attains the necessary four additional electrons, completing its outer electron shell. Each hydrogen atom also gains an electron in this process, resulting in each hydrogen having 2 electrons.

NH3 (Ammonia):

• Ammonia (NH3) consists of one nitrogen (N) atom sharing three electron pairs with three hydrogen (H) atoms. Nitrogen has 7 electrons in its ground state and requires three more electrons to achieve the electron configuration of neon (Ne), which is stable with 10 electrons and a full 2p orbital. By sharing three electron pairs with the hydrogen atoms, nitrogen acquires the necessary three additional electrons, completing its outer electron shell. Each hydrogen atom receives an electron in this process, resulting in each hydrogen having 2 electrons.

HCl (Hydrogen Chloride):

• Hydrogen chloride (HCl) is formed when one hydrogen (H) atom shares one electron pair with one chlorine (Cl) atom. Hydrogen has 1 electron in its ground state and needs one more electron to achieve the electron configuration of helium (He), which is stable with 2 electrons and a full 1s orbital. By sharing one electron pair with the hydrogen atom, chlorine attains the necessary electron, completing its outer electron shell. The hydrogen atom gains an electron in this process, resulting in the hydrogen having 2 electrons (like helium), and chlorine has 8 electrons (like argon).

In summary, the covalent bonding allows atoms to share electrons in pairs, resulting in each atom achieving a stable noble gas-like electron configuration. The table shows how this electron sharing occurs in some simple molecules.

Differences in Volatility, Solubility, and Electrical Conductivity between Ionic and Covalent Compounds:

Volatility:

• Ionic Compounds: Generally have high melting and boiling points, making them less volatile at room temperature.
• Covalent Compounds: Tend to have lower melting and boiling points, making them more volatile at room temperature.

• Solubility:
  • Ionic Compounds: Often dissolve well in polar solvents due to the attraction between ions and solvent molecules.
  • Covalent Compounds: Tend to be more soluble in nonpolar solvents due to their similar nature.

• Electrical Conductivity (in the solid state):
  • Ionic Compounds: Poor conductors of electricity in the solid state as their ions are fixed in the lattice and cannot move.
  • Covalent Compounds: Poor conductors of electricity in the solid state since they lack free mobile charged particles.

• Electrical Conductivity (in the liquid or dissolved state):
  • Ionic Compounds: Conduct electricity when dissolved in water or melted, as their ions become free to move and carry electric charges.
  • Covalent Compounds: Conduct electricity to a limited extent when dissolved in water if they dissociate into ions, but most covalent compounds do not conduct electricity.

• State at Room Temperature:
  • Ionic Compounds: Often exist as solids at room temperature due to their high melting points.
  • Covalent Compounds: Can exist as solids, liquids, or gasses at room temperature, depending on their molecular structure and intermolecular forces.

• Structure:
  • Ionic Compounds: Composed of ions arranged in a lattice structure held together by electrostatic forces.
  • Covalent Compounds: Formed by the sharing of electrons between atoms, resulting in discrete molecules.

• Melting and Boiling Points:
  • Ionic Compounds: Generally have higher melting and boiling points due to strong ionic bonds.
  • Covalent Compounds: Tend to have lower melting and boiling points due to weaker intermolecular forces.

• Conductivity in the Gaseous State:
  • Ionic Compounds: Generally do not conduct electricity in the gaseous state since the ions are not free to move.
  • Covalent Compounds: Do not conduct electricity in the gaseous state as they lack mobile charged particles.