Untitled Quiz

Atomic and Molecular Orbitals

• Atomic orbitals represent the wave function of an electron in an atom and are mono-centric.
• Molecular orbitals arise from the combination of atomic orbitals in molecules and are polycentric.
• Bonding and anti-bonding molecular orbitals exist, with bonding orbitals being more stable and having a complex shape compared to atomic orbitals, which are designated as s, p, d, f and molecular orbitals as , *, , *, , *.

Scientific Method

• Science is defined as organized knowledge based on observations, tested and verified.
• The first step involves observing phenomena and attempting to formulate general statements known as laws.
• A hypothesis is an imaginative explanation of observed facts; for instance, Dalton’s atomic hypothesis.
• Testing a hypothesis can elevate it to theory if proven correct, but direct proof of theories like the kinetic theory of gases is challenging.

Atomic Structure and Models

• Atoms are the fundamental units of elements that participate in chemical reactions, proposed initially by John Dalton in 1808 as indivisible.
• By the late 19th century, atoms were proven to consist of electrons, protons, and neutrons, leading to questions of atomic structure highlighted by models such as Thomson's, Rutherford’s, and Bohr's.

Electromagnetic Radiations

• James Clerk Maxwell demonstrated that alternating currents can produce electromagnetic waves, carrying electric and magnetic properties.
• Electromagnetic waves include visible light, ultraviolet, infrared, and X-rays, traveling at the speed of light (3.0 x 10^10 cm/s).
• Key characteristics of waves:
  • Wavelength (λ), the distance between crests (1 Å = 10^-8 cm).
  • Frequency (υ), the number of wave cycles per second (measured in Hz).
  • Wavenumber, reciprocal of wavelength.
  • Amplitude (a), the height of the crest.
  • Velocity (c), the speed of the wave, expressed by the relation c = υλ.

Electromagnetic Spectrum

• The electromagnetic spectrum organizes radiations by wavelength or frequency.
• Visible light lies between wavelengths of 3800-7600 Å.
• The order of increasing wavelength: γ-rays < X-rays < UV rays < Visible rays < IR rays.

Molecular Orbital Combinations

• Combinations of atomic orbitals yield molecular orbitals: bonding σ, anti-bonding σ*, bonding π, and anti-bonding π*.
• Different combinations result from end-to-end or side-by-side overlaps.
• S-orbitals form bonding molecular orbitals through wave function addition and anti-bonding by subtraction.
• P-orbitals can form bonding and anti-bonding through similar interactions.

Molecular Orbital Configurations

• Nitrogen (N2) configuration: (1s)²(2s)²(2p)², gives a bond order of 3; it is diamagnetic with no unpaired electrons.
• Oxygen (O2) configuration: (1s)²(2s)²(2p)⁴, bond order of 2; it is paramagnetic due to unpaired electrons.
• Nitric oxide (NO) configuration: bond order of 2.5; it is also paramagnetic.
• Carbon monoxide (CO): bond order of 3; it is stable and diamagnetic with no unpaired electrons.

Crystal Field Theory (CFT)

• Proposed by Bethe and Van Vleck, extended by Orgel, applicable to transition metals.
• Treats the metal ion as a point charge and surrounding ligands as point masses.
• In octahedral complexes, t2g orbitals are raised in energy due to proximity to ligands.
• Tetrahedral splitting energy (∆t) is significantly less than octahedral splitting energy (∆o).

Pi Molecular Orbitals of Butadiene

• Butadiene features two adjacent pi-bonds and consists of 4 p-orbitals.
• The formation of pi molecular orbitals involves aligning p-orbitals in phase, with increasing node count leading to higher energy orbitals.
• The highest occupied molecular orbital (HOMO) of butadiene is π2, while the lowest unoccupied (LUMO) is π3.

Pi Molecular Orbitals of Benzene

• Benzene exhibits sp2 hybridization with a planar structure, having equal carbon-carbon bond lengths.
• In benzene, p-orbitals overlap to form three bonding and three anti-bonding molecular orbitals, contributing to the understanding of aromaticity.