Chemical Bonding Lecture Notes

Comprehensive flashcards covering Chemical Bonding, VBT, VSEPR, hybridisation, molecular parameters, oxy-acids, and allotropes from the Allen Career Institute Inorganic Chemistry notes.

Chemical bond

The attractive force which holds various constituents (atoms, ions, etc.) together in different chemical species, accompanied by a decrease in energy.

Octet Rule

The tendency of atoms to combine to complete an octet of electrons ($ns^2np^6$) in their outermost shell to attain a noble gas configuration.

Hypovalent compounds

Compounds characterized by a contraction of the octet (incomplete octet) at the central atom, such as $BeF_2$ ($4e^-$) and $BF_3$ ($6e^-$).

Hypervalent compounds

Compounds showing an expansion of the octet due to empty d-orbitals, resulting in more than 8 electrons at the central atom, such as $PCl_5$ ($10e^-$) and $SF_6$ ($12e^-$).

Pseudo inert gas configuration

An electronic configuration represented as $[(ns^2np^6nd^{10})]$, found in ions like $Zn^{2+}$ and $Cd^{2+}$.

Ionic or electrovalent bond

A chemical bond formed between two or more atoms as a result of the complete transfer of one or more electrons from one atom to another.

Electrovalency

The number of electrons lost or gained by an atom during the formation of an ionic bond; for example, the electrovalency of $Mg$ in $MgO$ is 2.

Covalent bond

A directional chemical bond formed by the mutual sharing of electrons between two atoms.

Covalency

The capacity of an atom to form covalent bonds, represented by small lines (single, double, or triple bonds).

Coordinate Bond (Dative Bond)

A bond formed between two atoms where the contribution of an electron pair is made by one atom (the donor) while the sharing is done by both.

Formal Charge ($Q_F$)

The charge assigned to an atom in a molecule, calculated as $Q_F = N_A - N_{L.P.} - \frac{1}{2} N_{B.P.}$, where $N_A$ is valence electrons, $N_{L.P.}$ is lone pair electrons, and $N_{B.P.}$ is bonding electrons.

Resonance

A phenomenon where a molecule cannot be represented by a single Lewis structure but is described as a resonance hybrid of two or more contributing (canonical) structures.

Bond Length

The equilibrium internuclear distance at minimum potential energy between two bonded atoms in a molecule.

Bond Dissociation Energy (B.D.E.)

The amount of energy released when one mole of a specific type of bond is formed, or required to dissociate one mole of bonds in a gaseous state.

Orbital Overlap Concept

The partial merging of atomic orbitals resulting in the pairing of electrons with opposite spins; the extent of overlap determines the strength of the covalent bond.

Sigma (\text{\sigma}) Bond

A covalent bond formed by the end-to-end (head-on or axial) overlap of bonding orbitals along the internuclear axis.

Pi ($\pi$) Bond

A covalent bond formed by sidewise (lateral) overlap where atomic orbital axes remain parallel to each other and perpendicular to the internuclear axis.

Delta (\text{\delta}) Bond

Covalent bonds where four lobes of a d-orbital of one atom overlap with four lobes of a similar d-orbital of another atom; formed by all d-orbitals except $d_{z^2}$.

Hybridisation

The phenomenon of intermixing orbitals of slightly different energies to redistribute their energies and form a new set of equivalent orbitals in shape and energy.

Steric Number (S.N.)

The formula used to predict the hybridisation state, calculated as: \text{Number of } \text{\sigma-bond around that atom} + \text{Number of lone pair on that atom}.

VSEPR Theory

Valence Shell Electron Pair Repulsion theory, which predicts molecular shape by minimizing repulsions between electron pairs in the valence shell.

Bond Order

The number of bonds between two atoms in a molecule; for example, $H_2$ has a bond order of 1, $O_2$ is 2, and $N_2$ is 3.

Bent’s Rule

States that a lone pair prefers to occupy hybrid orbitals with greater s-character, while more electronegative atoms prefer orbitals with smaller s-character.

Drago’s Rule

Suggests that for central atoms of the 3rd period or lower with at least one lone pair and surrounding atoms with electronegativity $\le 2.5$, no hybridisation occurs and bond angles are approximately $90^\circ$.

Dipole Moment (\text{\mu})

A vector quantity representing the degree of polarity of a covalent bond, calculated as the product of charge (\text{\delta}) and distance ($d$): \text{\mu} = \text{\delta} \times d.

Hydrogen Bonding

A weak electrostatic force of attraction developed when a hydrogen atom bonded to a highly electronegative atom (F, O, or N) comes under the influence of another electronegative atom.

Metallic bond

Attractive forces between metal kernels at lattice sites and less firmly held valence electrons, described by the electron gas or sea model.

Vander Waal’s Forces

The weakest types of non-directional, non-valence cohesive intermolecular forces, including Keesom, Debye, and London forces.

Keesom forces

Dipole-dipole interactions characterized by the attraction between oppositely charged poles of two polar molecules like $HCl$ or $H_2S$.

London forces (Dispersion forces)

Weak intermolecular forces arising from instantaneous dipole-induced dipole interactions, operating in both polar and non-polar species.

Basicity of an acid

The number of acidic hydrogen atoms attached to oxygen in an oxy-acid that can ionize in solution.

Pyro acid

An oxy-acid formed when one mole of water is removed from two moles of an oxy-acid, generally containing $X-O-X$ bonds.

Hypo acid

An oxy-acid obtained by removing one oxygen atom from the '-ous' form of an acid; for example, $H_3PO_2$ is hypophosphorous acid.

Meta acid

The product formed when one mole of $H_2O$ is removed from one mole of an ortho acid.

Peroxy acid

Acids containing a peroxy linkage ($-O-O-$), formed when one oxygen is added to the '-ic' form of an acid without changing the central atom's oxidation state.

Thio acid

Oxy-acids in which one or more oxygen atoms are replaced by sulphur, or oxy-acids of sulphur specifically containing $S-S$ bonds.

Silicates

Metal derivatives of silicic acid ($H_4SiO_4$) consisting of $SiO_4^{4-}$ tetrahedral units bonded in various patterns (ortho, pyro, cyclic, chain, sheet, or 3D).

Graphite

The thermodynamically most stable allotrope of carbon, featuring a layered structure with $sp^2$ hybridised carbon atoms in hexagonal rings.

Fullerene $C_{60}$

Also called Buckminsterfullerene; a soccer ball-shaped molecule with 20 six-membered and 12 five-membered rings, where carbon atoms are $sp^2$ hybridised.

Transition temperature (Sulphur)

The temperature ($369,K$) at which both rhombic (\text{\alpha}-sulphur) and monoclinic (\text{\beta}-sulphur) forms are stable.

Chemiluminescence

The property of glowing in the dark, specifically exhibited by white phosphorus.