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Questions and Answers
Which molecule is an example of having an odd number of electrons?
Which molecule is an example of having an odd number of electrons?
- BF₃
- H₂O
- ClO₂ (correct)
- PCl₅
Which statement describes a situation where an atom has fewer than eight electrons?
Which statement describes a situation where an atom has fewer than eight electrons?
- NO₂ has a full octet around nitrogen.
- NH₄⁺ has eight electrons surrounding nitrogen.
- BF₃ has six electrons around the boron atom. (correct)
- PCl₅ possesses an expanded octet.
What is a defining feature of molecules with more than an octet?
What is a defining feature of molecules with more than an octet?
- They must have unpaired electrons.
- They always form ionic bonds.
- They contain atoms with fewer than four valence electrons.
- They can have up to ten valence electrons in the outer shell. (correct)
Which of the following correctly identifies a limitation of the octet rule?
Which of the following correctly identifies a limitation of the octet rule?
What electronic configuration does hydrogen achieve when it shares electrons in NH₃?
What electronic configuration does hydrogen achieve when it shares electrons in NH₃?
What is the primary driving force for chemical interactions between atoms?
What is the primary driving force for chemical interactions between atoms?
What happens when the overlapping orbitals have the same sign?
What happens when the overlapping orbitals have the same sign?
Which of the following statements is correct regarding the stability of the H₂+ ion?
Which of the following statements is correct regarding the stability of the H₂+ ion?
What does zero overlap of orbitals result in?
What does zero overlap of orbitals result in?
How does increased electron density affect the interaction between two nuclei?
How does increased electron density affect the interaction between two nuclei?
Which expression correctly characterizes the interaction when there is negative overlap?
Which expression correctly characterizes the interaction when there is negative overlap?
What is the effect of overlapping orbitals on the electron density between atomic cores?
What is the effect of overlapping orbitals on the electron density between atomic cores?
What occurs when two orbitals overlap with opposite signs?
What occurs when two orbitals overlap with opposite signs?
What phenomenon occurs when the net overlap of electron density is zero?
What phenomenon occurs when the net overlap of electron density is zero?
What does Pauling's definition of electronegativity focus on?
What does Pauling's definition of electronegativity focus on?
According to Pauling, an electronegativity difference greater than 1.7 indicates which of the following?
According to Pauling, an electronegativity difference greater than 1.7 indicates which of the following?
How is Robert Mulliken's definition of electronegativity characterized?
How is Robert Mulliken's definition of electronegativity characterized?
Which statement about electronegativity is true regarding elements close to fluorine?
Which statement about electronegativity is true regarding elements close to fluorine?
What is described as the octet rule?
What is described as the octet rule?
What aspect of electronegativity is emphasized by A.L. Allred and E. Rochow's definition?
What aspect of electronegativity is emphasized by A.L. Allred and E. Rochow's definition?
What application of electronegativity involves understanding the polarity of molecules?
What application of electronegativity involves understanding the polarity of molecules?
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Study Notes
Driving Forces for Chemical Interactions
- Coulombic attraction and repulsion forces between the nucleus and electrons of two or more atoms cause chemical interactions.
- Chemical interactions occur when the outer orbitals of different atoms overlap, concentrating electron density between the atomic cores.
- Positive overlap increases electron density between the atomic cores resulting in a stronger attractive force.
- Negative overlap reduces electron density between the atomic cores leading to a repulsive force.
- Zero overlap results in a non-bonding interaction as there is neither attraction nor repulsion between the atoms.
Electronegativity
- Electronegativity refers to the power of an atom of an element to attract electrons in a compound.
- Pauling's electronegativity difference between two atoms is 0.180 Δ, where Δ is the resonance energy in kcal/mol, calculated from bond energy difference.
- A difference in electronegativity smaller than 1.7 indicates a covalent bond, while a difference greater than 1.7 indicates an ionic bond.
- Mulliken's electronegativity, Xm, is the average of the ionization energy and electron affinity.
- Allred and Rochow calculated electronegativity based on the electric field at the surface of an atom, using the effective nuclear charge and covalent radius.
Applications of Electronegativity
- Electronegativity can be used to understand bond energies, predict the polarity of bonds and molecules, and rationalize the types of chemical reactions.
Octet Rule
- Atoms tend to gain, lose, or share electrons to achieve a stable configuration of eight electrons in their valence shell.
- This rule applies mostly to representative elements but has exceptions.
Exceptions to the Octet Rule
- Odd Number of Electrons: Molecules like NO or ClO₂ with an odd number of electrons can't achieve complete pairing and an octet around each atom.
- Less than an Octet: Atoms like boron in BF₃ have less than eight electrons in their valence shell.
- More than an Octet: Atoms like phosphorus in PCl₅ expand their valence shell to accommodate more than eight electrons.
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