chem bond

• Octet rule: During a chemical reaction, atoms tend to adjust their electronic arrangement to achieve 8 electrons in their outermost shell
• Chemical bond: The force that keeps atoms in a molecule together
• Ionic bond: Formed by the complete transfer of one or more electrons from a metal atom to a non-metal atom
• Lattice enthalpy: The molar enthalpy change accompanying the complete separation of constituent particles in solids under standard conditions
• Electrovalency: The number of electrons lost or gained by an atom of an element
• Formation of an ionic bond is favored by:

  • Low ionization enthalpy of a metallic element forming cations
  • High electron gain enthalpy of non-metallic element forming anions
  • Large lattice enthalpy due to smaller size and higher charge of atoms
• Covalency: The number of electrons an atom contributes towards mutual sharing during bond formation
• Single covalent bond: Formed by the mutual sharing of one pair of electrons, represented by a small line (-) between the two atoms
• Double covalent bond: Formed by the mutual sharing of two pairs of electrons, represented by two small horizontal lines (=) between the two atoms
• Triple covalent bond: Formed by the mutual sharing of three pairs of electrons, represented by three small horizontal lines (≡) between the two atoms
• Formation of a covalent bond is favored by:

  • High ionization enthalpy of combining elements
  • Nearly equal electron gain enthalpy and electronegativities of combining elements
  • High nuclear charge and small atomic size of combining elements
• Polar covalent bond: Between two unlike atoms differing in their affinities for electrons
• Coordinate bond: Formed when one-sided sharing of electrons occurs, also known as a dative bond
• Bond length: Equilibrium distance between nuclei of two bonded atoms in a molecule
• Bond angle: Angle between orbitals containing bonding electron pairs around the central atom in a molecule or complex ion
• Bond enthalpy: Energy required to break one mole of bonds of a particular type between two atoms in a gaseous state
• Bond order: Given by the number of bonds between two atoms in a molecule in the Lewis description of a covalent bond
• Resonance: When a single Lewis structure cannot accurately describe a molecule, multiple structures are considered as canonical structures of the hybrid
• Dipole moment: Product of the charge magnitude and distance between the centers of positive and negative charge, represented by an arrow
• Sigma bond: Formed by overlapping of orbitals along the line joining the two nuclei, such as s-s and s-p, p-p overlapping
• Pi bond: Formed by the sideways overlapping of p- or d-orbitals of two atoms
• Hydrogen bond: Between a hydrogen atom of one molecule and a more electronegative element of the same or another molecule
• Hybridization: Mixing of atomic orbitals to form new hybrid orbitals with equal energy, identical shapes, and symmetric orientation
• Molecular geometry examples:

  • Linear: BeCl2, HgCl2, CO2
  • Bent: NO2-, SO2, O3, CCl2
  • Trigonal planar: BF3, CO32-, NO3-, SO3
  • Trigonal pyramidal: NH3, PCl3
• One-mark questions:

  • Total number of sigma and pi bonds in C2H2 and C2H4
  • Significance of plus and minus signs in representing orbitals
  • Expressing bond strength in terms of bond order
  • Definition of bond length
  • Arranging bonds in order of increasing ionic character in molecules
  • Correct Lewis structure for acetic acid
• The order of increasing ionic character in the molecules: LiF, K2O, N2, SO2, and ClF3 is N2 < SO2 < ClF3 < K2O < LiF
• The correct Lewis structure for acetic acid is determined by ensuring the bonds are shown correctly
• The octet rule states that elements tend to adjust the arrangement of their electrons to achieve eight electrons in their outermost shell, except for H and He
• Lattice enthalpy is defined as the energy required when one mole of an ionic compound in crystalline form is split into the constituent ions
• A covalent bond is formed when atoms have zero difference in electronegativity
• A hydrogen bond is an attractive force between the hydrogen attached to an electronegative atom of one molecule and an electronegative atom of a different molecule
• Factors favoring the formation of an ionic bond include low ionization enthalpy of the metal atom, high electron gain enthalpy of a non-metal atom, and high lattice energy of the compound formed
• The bond angle in water is less than that of ammonia due to the repulsions on the bond pairs in H2O being greater than in NH3
• Resonance in the carbonate ion is explained by it being a resonance hybrid of different structures
• The given structures for H3PO3 cannot be taken as canonical forms of the resonance hybrid because the positions of the atoms have changed
• The significance of dipole moment lies in its use to differentiate between polar and non-polar bonds and in calculating the percentage ionic character of a molecule
• The Be2 molecule does not exist due to its unstable bond order of zero
• Sigma bonds are formed by end-to-end overlap of orbitals, while pi bonds are formed by lateral overlap of orbitals
• A polar covalent bond forms when two dissimilar atoms with different electronegativities combine, resulting in an unequal sharing of the bond pair
• In the formation of an ethane molecule (C2H4), one sp2 hybrid orbital of carbon overlaps a sp2 hybridized orbital of another carbon atom, forming a C-C sigma bond