#chemistry #bonding #covalentbonding #covalent #textbook #igcse

Pg:- 48.49,50,51,52,53,54,55,56

Ch:- 4

Covalent bonding is a type of chemical bond that occurs when two atoms share one or more pairs of electrons to achieve a more stable electronic configuration, typically achieving a full outer electron shell. This sharing of electrons allows the atoms involved to attain the electronic structure of a noble gas, which is energetically favorable.

How Covalent Bonds Form

• Electron Sharing: In a covalent bond, the electrons are not transferred (as in ionic bonding) but rather shared between two atoms. Each atom contributes at least one electron to form a shared pair, creating a bond.

• Octet Rule: Atoms form covalent bonds to satisfy the octet rule, which states that atoms tend to bond in such a way that they have eight electrons in their outermost shell (valence shell), making them more stable. For hydrogen, however, the goal is to have two electrons in its outer shell (a duet).

Types of Covalent Bonds

A simple covalent bond is a chemical bond where two atoms share a pair of electrons to achieve a more stable electron configuration. This type of bond typically forms between nonmetal atoms, allowing each to fill its outer electron shell, often following the octet rule. An example is the bond in a hydrogen molecule (H₂), where two hydrogen atoms each share one electron to form a stable H-H bond.

Covalent bonds can be single, double, or triple, depending on the number of shared electron pairs. Simple covalent bonds are generally strong, and directional, and form distinct molecules like water (H₂O) and oxygen (O₂).

1. Single Bond: This involves one pair of shared electrons. An example is the bond between two hydrogen atoms in a hydrogen molecule (H₂).

2. Double Bond: Involves two pairs of shared electrons. For example, in an oxygen molecule (O₂), two oxygen atoms share two pairs of electrons.

3. Triple Bond: Involves three pairs of shared electrons, such as in a nitrogen molecule (N₂).

4. Polar vs. Nonpolar Covalent Bonds:

   • Nonpolar Covalent Bond: If the atoms sharing electrons have the same or very similar electronegativity (a measure of an atom’s ability to attract electrons), the shared electrons are distributed evenly. Examples include the bond in a hydrogen molecule (H₂) or methane (CH₄).

   • Polar Covalent Bond: If the atoms involved have different electronegativities, the electrons are shared unequally, creating a dipole with partial positive and negative charges on the atoms. Water (H₂O) is an example, where oxygen is more electronegative than hydrogen, leading to an uneven electron distribution.

Covalent Bond Characteristics

• Directional: Unlike ionic bonds, which form through electrostatic attraction in all directions, covalent bonds are directional and form between specific atoms.

• Molecular Formation: Covalent bonding typically results in the formation of molecules. For instance, H₂, O₂, and H₂O are examples of molecules formed through covalent bonding.

• Bond Strength: Covalent bonds are generally strong, with bond strength depending on the number of shared electron pairs. Triple bonds are stronger than double bonds, which in turn are stronger than single bonds.

• Bond Length: The distance between the nuclei of two bonded atoms is called the bond length. Triple bonds are shorter than double bonds, which are shorter than single bonds.

Examples of Covalent Bonding

1. Water (H₂O): Each hydrogen atom shares one electron with the oxygen atom, leading to two covalent bonds (H-O-H). Oxygen, with its higher electronegativity, pulls the shared electrons closer to itself, resulting in a polar covalent bond.

2. Methane (CH₄): Carbon shares its four outer electrons with four hydrogen atoms, resulting in four single covalent bonds. The bonding is nonpolar because the electronegativities of carbon and hydrogen are relatively similar.

3. Carbon Dioxide (CO₂): Carbon forms double bonds with two oxygen atoms, leading to a linear structure with two strong double bonds.

Bonding in Larger Structures

In some materials, particularly network covalent substances (e.g., diamond, silicon dioxide), covalent bonds extend in a 3D network. This results in extremely strong and hard materials because every atom is covalently bonded to multiple others, forming a continuous network.

Key Differences from Ionic Bonding

• In ionic bonding, atoms transfer electrons, leading to the formation of positive and negative ions that attract each other electrostatically.

• In covalent bonding, atoms share electrons to achieve stability, without forming ions.