COVALENT BONDS AND COMPOUNDS

Introduction

Covalent bonds are formed when two or more atoms share electrons to achieve a stable electron configuration. In a covalent bond, the shared electrons are attracted to the nuclei of both atoms, resulting in the formation of a stable molecule.

Covalent compounds are formed when atoms of different elements share electrons to form molecules. In a covalent compound, the atoms are held together by covalent bonds. Examples of covalent compounds include water (H2O), methane (CH4), and carbon dioxide (CO2).

The strength of a covalent bond depends on the number of shared electrons and the electronegativity of the atoms involved. Electronegativity is a measure of the tendency of an atom to attract electrons towards itself. When two atoms have similar electronegativities, the shared electrons are shared equally between them, forming a nonpolar covalent bond. When the electronegativities of the two atoms are different, the shared electrons are not shared equally, forming a polar covalent bond.

Covalent compounds have several properties, including a low melting and boiling point, and are typically gases or liquids at room temperature. They also tend to have low solubility in water and do not conduct electricity when dissolved in water or in the solid state.

 

The properties of covalent compounds can vary widely depending on the nature and arrangement of the atoms involved. Here are some general properties of covalent compounds:

1. Solubility in polar and non-polar solvents: Covalent compounds are generally insoluble in polar solvents such as water because they lack ionic charges to interact with the polar water molecules. However, some covalent compounds can be soluble in non-polar solvents such as hydrocarbons, where they can dissolve due to their non-polar nature.
2. Melting and boiling point: The melting and boiling points of covalent compounds are generally lower than those of ionic compounds. This is because the intermolecular forces of attraction in covalent compounds are generally weaker than those in ionic compounds, due to the lack of charged particles. Covalent compounds with stronger intermolecular forces, such as hydrogen bonding or dipole-dipole interactions, will have higher melting and boiling points than those with weaker intermolecular forces.
3. Electrical conductivity: Covalent compounds are generally poor conductors of electricity in their solid and liquid states because they lack charged particles. However, some covalent compounds can conduct electricity when they are in their molten or aqueous states. This is because the covalent bonds may break down, resulting in the formation of charged particles.
4. They have lower enthalpies of fusion and vaporization: Due to their weak intermolecular forces, covalent compounds require relatively little energy to melt or evaporate, resulting in lower enthalpies of fusion and vaporization compared to ionic compounds.
5. Covalent compounds are often volatile: Due to their weak intermolecular forces, many covalent compounds are volatile and can easily evaporate into the air. Examples include ammonia, methane, and ethanol.
6. Covalent compounds can be gases, liquids or solids: Depending on their properties and molecular structure, covalent compounds can exist in any of the three states of matter. For example, water is a covalent compound that is a liquid at room temperature and pressure, while carbon dioxide is a covalent compound that is a gas under the same conditions.
7. Soft and brittle: Covalent compounds are typically soft and brittle because the bonds between molecules are weak and can easily break under stress.

In summary, the solubility, melting and boiling points, and electrical conductivity of covalent compounds are generally lower than those of ionic compounds due to their weaker intermolecular forces and lack of charged particles. However, there are exceptions to these generalizations, and the properties of covalent compounds can vary widely depending on their specific structures and compositions.

 

Coordinate (dative) covalent bonding

 

Pure covalent and coordinate (dative) covalent bonds

A covalent bond is a type of chemical bond that involves the sharing of electrons between two atoms. Pure covalent and coordinate covalent (dative) bonds are two types of covalent bonds.

A pure covalent bond occurs when two atoms share electrons equally. This means that the atoms have the same electronegativity, or ability to attract electrons. In a pure covalent bond, the shared electrons spend equal time around each atom, creating a symmetrical electron distribution.

On the other hand, a coordinate covalent (dative) bond occurs when one atom donates a pair of electrons to another atom that needs them to complete its valence shell. The atom that donates the electrons is called the donor atom, and the atom that accepts the electrons is called the acceptor atom. The shared pair of electrons is held by the acceptor atom, forming a bond. This type of bond is often represented by an arrow pointing from the donor atom to the acceptor atom.

The main difference between pure covalent and coordinate covalent bonds is the way the electrons are shared. In a pure covalent bond, the electrons are shared equally between the atoms, while in a coordinate covalent bond, one atom donates a pair of electrons to another atom that needs them.

Another difference between the two types of bonds is their relative strength. Pure covalent bonds are typically weaker than ionic bonds but stronger than hydrogen bonds. Coordinate covalent bonds are generally stronger than pure covalent bonds because the acceptor atom has a greater attraction for the shared electrons than the donor atom.