Types of Bonds

Chemical bonding and molecular structure

A chemical bond is the force that holds atoms together in a molecule. It is the result of the interaction between atoms, which may involve the sharing or transfer of electrons.

Types of chemical bonds

1. Ionic/electrovalent bond
2. Covalent bond
3. Coordinate bond
4. Polar covalent bond
5. Non-polar covalent bond
6. Hydrogen bonding

Ionic/electrovalent bond

An ionic bond is formed by the complete transfer of one or more electrons from a metal atom to a non-metal atom.

Key Concepts

1. Electron Transfer: The metal atom loses electrons to become a positively charged ion (cation), while the non-metal atom gains electrons to become a negatively charged ion (anion).
2. Formation of Noble Gas Configurations: Both atoms acquire the stable electron configuration of the nearest noble gas.
3. Coulombic Attraction: The oppositely charged ions are held together by electrostatic forces.

Electrovalency: The number of electrons lost or gained by an atom to form ions.

Example

$Na + Cl \rightarrow Na^+Cl^-$ (Sodium chloride)

Factors Influencing Ionic Bond Formation

1. Ionization Energy: Energy required to remove an electron from an atom.
2. Electron Affinity: Energy released when an atom gains an electron.
3. Lattice Energy: Energy released when ions come together to form a lattice.

Covalent bond

A covalent bond is formed by the mutual sharing of electrons between two atoms.

Key Concepts

1. Covalency: The number of electrons an atom shares to form a bond.
2. Electron Sharing: Atoms share electrons to achieve a stable noble gas configuration.

Types of covalent bonds

1. Single Covalent Bond: Formed by sharing one pair of electrons. Example: $H_2$, $Cl_2$
2. Double Covalent Bond: Formed by sharing two pairs of electrons. Example: $O_2$, $CO_2$
3. Triple Covalent Bond: Formed by sharing three pairs of electrons. Example: $N_2$, $C\equiv C$ in acetylene

Properties of covalent bonds

1. Directional: The shared electron pair is localized between the nuclei.
2. Bond Strength: Triple bonds are stronger and shorter than double bonds, which are stronger and shorter than single bonds.

Factors Favoring Covalent Bond Formation

1. High ionization energy
2. Similar electron affinities
3. Equal or nearly equal electronegativity
4. High nuclear charge and small atomic size

Coordinate covalent bond

A coordinate bond forms when one atom donates both electrons in the shared pair.

Example: Ammonium ion ($NH_4^+$): The nitrogen atom donates the pair to the hydrogen ion ($H^+$).

Polar and non-polar covalent bonds

Non-polar Covalent Bond: Occurs when two identical atoms share electrons equally. Example:

Polar Covalent Bond: Occurs when two atoms with different electronegativities share electrons, resulting in a dipole (partial positive and negative charges). Example: $HCl$, $H_2O$

Electronegativity Difference: The greater the difference in electronegativity, the more polar the bond.

Valence Shell Electron Pair Repulsion (VSEPR) theory

VSEPR theory explains the shapes of molecules based on electron-pair repulsion. Electron pairs in the valence shell of atoms arrange themselves to minimize repulsion.

Key Points

1. Electron Pair Arrangement: Electron pairs around the central atom are arranged to be as far apart as possible.
2. Repulsion Strength Order: Lone pair-lone pair > lone pair-bond pair > bond pair-bond pair

Molecule shapes

1. Bond Pairs: Linear (180º). Example: $CO_2$

   

2. Bond Pairs: Trigonal Planar (120º). Example: $BF_3$

   

3. Bond Pairs: Tetrahedral (109.5º). Example: $CH_4$

   

4. Bond Pairs: Trigonal Bipyramidal (90º, 120º). Example: $PCl_5$

   

5. Bond Pairs: Octahedral (90º). Example: $SF_6$

   

Shapes of molecules with bond pairs and lone pair electrons

Lone pairs cause distortions in molecular geometry (e.g., bent shape in water).

1. Molecules with Three Bond Pairs and One Lone Pair: Triangular pyramidal shape. Example: $NH_3$, $NF_3$, $PCl_3$

   

2. Molecules with Two Bond Pairs and Two Lone Pairs: Bent shape. Example: $H_2O$, $H_2S$

   

3. Molecules with Four Bond Pairs and Two Lone Pairs: Square planar shape.