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Questions and Answers
What is the primary characteristic of electromagnetic waves regarding their propagation?
What is the primary characteristic of electromagnetic waves regarding their propagation?
Which term describes the distance between two consecutive crests or troughs of a wave?
Which term describes the distance between two consecutive crests or troughs of a wave?
How is frequency measured?
How is frequency measured?
What is the speed of electromagnetic waves in a vacuum?
What is the speed of electromagnetic waves in a vacuum?
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Which electromagnetic radiation has the shortest wavelength?
Which electromagnetic radiation has the shortest wavelength?
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What is the relationship defined by the equation $c =
u imes ext{λ}$ for waves?
What is the relationship defined by the equation $c = u imes ext{λ}$ for waves?
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Which best describes the electromagnetic spectrum?
Which best describes the electromagnetic spectrum?
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What is amplitude in the context of wave properties?
What is amplitude in the context of wave properties?
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What describes the wave function signs of s-orbitals?
What describes the wave function signs of s-orbitals?
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What type of molecular orbital is formed when two positive lobes combine?
What type of molecular orbital is formed when two positive lobes combine?
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What is the result of combining one positive lobe and one negative lobe from two p-orbitals?
What is the result of combining one positive lobe and one negative lobe from two p-orbitals?
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In a non-bonding combination, what happens to overall energy?
In a non-bonding combination, what happens to overall energy?
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Which combination of p-orbitals results in a bonding sigma molecular orbital?
Which combination of p-orbitals results in a bonding sigma molecular orbital?
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What is indicated by a nodal line in a molecular orbital?
What is indicated by a nodal line in a molecular orbital?
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Which type of overlap leads to anti-bonding molecular orbitals in p-orbital combinations?
Which type of overlap leads to anti-bonding molecular orbitals in p-orbital combinations?
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How are molecular orbitals formed from two 1s atomic orbitals described?
How are molecular orbitals formed from two 1s atomic orbitals described?
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What is the primary function of molecular orbitals in a molecule?
What is the primary function of molecular orbitals in a molecule?
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Which designation is used for atomic orbitals?
Which designation is used for atomic orbitals?
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Which step follows establishing a hypothesis in scientific development?
Which step follows establishing a hypothesis in scientific development?
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Who proposed the first atomic theory in 1808?
Who proposed the first atomic theory in 1808?
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What does a law in science represent?
What does a law in science represent?
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What happens if the assumptions of a hypothesis are supported by testing?
What happens if the assumptions of a hypothesis are supported by testing?
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Which atomic model was proposed by J.J. Thomson?
Which atomic model was proposed by J.J. Thomson?
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What fundamental particles make up an atom?
What fundamental particles make up an atom?
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How many electrons are present in the molecular orbitals of nitrogen molecules (N2)?
How many electrons are present in the molecular orbitals of nitrogen molecules (N2)?
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What is the bond order of the oxygen molecule (O2)?
What is the bond order of the oxygen molecule (O2)?
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Why is the nitrogen molecule (N2) considered diamagnetic?
Why is the nitrogen molecule (N2) considered diamagnetic?
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How many valence electrons are present in the nitric oxide molecule (NO)?
How many valence electrons are present in the nitric oxide molecule (NO)?
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What electronic configuration represents the oxygen molecule (O2)?
What electronic configuration represents the oxygen molecule (O2)?
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What is the bond order of carbon monoxide (CO)?
What is the bond order of carbon monoxide (CO)?
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What characteristic makes the nitric oxide molecule (NO) paramagnetic?
What characteristic makes the nitric oxide molecule (NO) paramagnetic?
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Which theory primarily applies to transition metals and involves point charges for metal ions?
Which theory primarily applies to transition metals and involves point charges for metal ions?
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What is the relationship between tetrahedral splitting energy (∆t) and octahedral splitting energy (∆o)?
What is the relationship between tetrahedral splitting energy (∆t) and octahedral splitting energy (∆o)?
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Why are low spin configurations rarely observed in tetrahedral complexes?
Why are low spin configurations rarely observed in tetrahedral complexes?
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What is the highest-occupied molecular orbital (HOMO) of butadiene?
What is the highest-occupied molecular orbital (HOMO) of butadiene?
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How many nodes does the highest-energy molecular orbital (π4) of butadiene have?
How many nodes does the highest-energy molecular orbital (π4) of butadiene have?
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Which description best fits the molecular orbital structure of benzene?
Which description best fits the molecular orbital structure of benzene?
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How many molecular orbitals does the cyclic array of p-orbitals in benzene produce?
How many molecular orbitals does the cyclic array of p-orbitals in benzene produce?
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What characterizes the molecular orbitals generated from the p-orbitals in benzene?
What characterizes the molecular orbitals generated from the p-orbitals in benzene?
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What is the lowest-unoccupied molecular orbital (LUMO) of butadiene?
What is the lowest-unoccupied molecular orbital (LUMO) of butadiene?
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Study Notes
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.
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