Brief Summary
Alright ji, here's the summary of the chemical bonding video, একদম ঝাক্কাস! We'll cover chemical bonds, octet rule, its limitations, types of bonds (ionic, covalent, coordinate), formal charge, dipole moment, and Fajan's rule. Buckle up!
- Chemical bonds are forces that hold atoms or ions together.
- Octet rule states atoms combine to achieve eight electrons in their outer shell.
- Limitations of octet rule: incomplete octet, odd electron molecules, expanded octet.
- Types of chemical bonds: ionic, covalent (polar & non-polar), coordinate.
- Bond parameters: bond length, bond angle, bond enthalpy, bond order.
Chemical Bonds and Octet Rule
Chemical bond is the force of attraction that holds atoms or ions together. The video then introduces the octet rule, which states that during molecule formation, atoms lose, gain, or share electrons to achieve eight electrons in their outermost shell. Sodium (Na), with an electronic configuration of 2, 8, 1, donates one electron to chlorine (Cl), which has seven electrons in its outermost shell. This results in Na becoming positively charged (Na+) and Cl becoming negatively charged (Cl-). Oxygen atoms combine by sharing electrons to form O2 molecules, resulting in a double bond.
Limitations of the Octet Rule
The octet rule has limitations. Some molecules have an incomplete octet, meaning the central atom has fewer than eight electrons. Examples include BeCl2 and BF3. Odd electron molecules, like NO and NO2, have an odd number of electrons. Expanded octets occur when the central atom has more than eight electrons, as seen in PF5, SF6, and sulfuric acid. The octet rule fails to explain the chemical inertness of noble gases, as xenon (Xe) can form compounds with highly electronegative elements like fluorine and oxygen. The octet rule doesn't provide information about the size, shape, stability, or energy of molecules; it only helps in drawing structures.
Types of Chemical Bonds
There are mainly three types of chemical bonds: ionic, covalent, and coordinate. Covalent bonds are further divided into polar and non-polar covalent bonds. Ionic bonds are formed by the transfer of electrons from a metal to a non-metal, requiring a large difference in electronegativity. For example, in NaCl formation, sodium loses an electron, requiring ionization enthalpy, and chlorine gains an electron. Lattice enthalpy is the energy required to separate one mole of a solid ionic compound into its gaseous ions. Covalent bonds involve the sharing of electron pairs between atoms. If one pair of electrons is shared, it's a single bond (e.g., Cl-Cl). Sharing two pairs forms a double bond (e.g., O=O), and sharing three pairs forms a triple bond (e.g., N≡N). Covalent bonds usually form between non-metals. Coordinate bonds (also known as dative bonds) involve one atom donating both electrons for sharing. Oxygen-containing compounds often form coordinate bonds. For example, in the formation of NH4+, nitrogen donates its lone pair to H+.
Formal Charge
Formal charge is calculated using the formula: Formal Charge = Valence Electrons - (Lone Pair Electrons + 1/2 * Bonding Electrons). For ozone (O3), the formal charges on the oxygen atoms are calculated. The central atom generally carries a positive charge.
Bond Parameters: Bond Length
Bond parameters include bond length, bond angle, bond enthalpy, and bond order. Bond length is the equilibrium distance between the nuclei of two bonded atoms. It is measured using techniques like spectroscopy and X-ray diffraction. Factors affecting bond length include the size of atoms (directly proportional) and bond order (inversely proportional). Electronic repulsion is directly proportional to bond length. Resonance and hyperconjugation are inversely proportional to bond multiplicity. Covalent radius is half the internuclear distance between two bonded atoms. Van der Waals radius is half the distance between the nearest similar atoms in separate molecules in a solid.
Bond Parameters: Bond Angle and Enthalpy
Bond angle is the angle between orbitals containing bonding electron pairs around the central atom. It determines the shape of the molecule. Bond angle depends on factors like hybridization, surrounding atoms, and the number of lone pairs. Bond enthalpy is the energy required to break one mole of covalent bonds between two atoms. For molecules with multiple bonds, average bond enthalpy is considered. Bond order is the number of bonds between two atoms in a molecule. Bond energy is directly proportional to bond order and inversely proportional to bond length and the number of lone pairs.
Bond Energy and Angle Relationships
Bond energy is directly proportional to bond order and polarity, but inversely proportional to bond length and lone pairs of electrons. There are exceptions in halogens. Bond angle is directly proportional to bond order and the electronegativity of terminal atoms, but inversely proportional to the size of the central atom.
