Chemical Bonding I: Lewis Model and VSEPR Theory

A collection of flashcards covering key concepts from Chapter 5 on Chemical Bonding, including Lewis Structures and VSEPR Theory.

What is the key concept of the Lewis Model?

Lewis structures provide a way to visualize molecular bonding and electron arrangements.

What does VSEPR stand for?

Valence Shell Electron Pair Repulsion Theory.

What happens if electrons in a bond are not shared equally?

The bond is polarized.

How is polarity in a chemical bond quantified?

By its dipole moment.

What does electronegativity measure?

The ability of an atom in a molecule to attract bonding electrons.

What are the three types of bonds classified by electronegativity difference (ΔX)?

1. Nonpolar covalent (0 ≤ ΔX ≤ 0.4), 2. Polar covalent (0.4 < ΔX < 2.0), 3. Ionic (2.0 ≤ ΔX).

Which element is the most electronegative?

Fluorine.

What is a dipole?

A separation of charge over some distance in a molecule.

How do you define a formal charge?

Formal charge = # of valence electrons on neutral atom - # of unshared electrons - 1/2(# of shared electrons).

What signifies a radical in terms of electron count?

Molecules with an odd number of valence electrons.

What is the octet rule?

Atoms tend to form bonds in such a way that they each have eight electrons in their valence shell.

What type of electrons do Lewis structures account for?

Valence electrons.

How do you choose the central atom in Lewis structures?

Typically the least electronegative element, never hydrogen.

What must be done to the total number of valence electrons after bonding in Lewis structures?

Subtract the number of bonded electrons from the total.

What happens if the central atom in a Lewis structure has an incomplete octet?

Double bonds may be formed using lone pairs from peripheral atoms.

How do you calculate the best representation of a molecule in terms of formal charge?

Lowest formal charge values closest to zero, negative formal charges on the most electronegative elements.

What is a resonance structure?

One of two or more valid Lewis structures for the same molecule.

What is the significance of resonance hybrid structures?

Represent the average of all acceptable resonance structures.

What defines isomers?

Compounds with the same molecular formula but different arrangements of atoms.

What do organic compounds generally consist of?

A framework of carbon atoms with N, O, H, and other elements attached.

What is the electron pair geometry for a molecule with two electron domains?

Linear with a 180° bond angle.

What determines the molecular geometry in VSEPR theory?

Electron pair geometry and the arrangement of bonded atoms.

How does the presence of lone pairs affect bond angles?

Lone pairs exert more repulsion, reducing bond angles between bonded pairs.

What is a tetrahedral molecular geometry and its ideal bond angle?

Four electron domains with an ideal bond angle of 109.5°.

What type of electron pair geometry is associated with five electron domains?

Trigonal bipyramidal.

What angle measures are associated with octahedral electron pair geometry?

90° and 180°.

What is the difference between molecular geometry and electron pair geometry?

Molecular geometry considers only bonded atoms, while electron pair geometry considers lone pairs and bonds.

How are polar molecules aligned in an electric field?

They tend to feel a force and align with the field.

What is the relationship between molecular polarity and boiling/melting points?

Polarity affects measurable properties such as boiling/melting points.

What analogy is used to explain molecular polarity?

A tug-of-war game where stronger side pulls more.

What does the overall orientation of bond dipoles determine?

The net dipole moment of the molecule.

What is the outcome of having equally polarized bonds in a molecule?

The molecule is nonpolar.

How does VSEPR theory approach resonance?

It allows for representations of resonance within the 3D structure.

In VSEPR, what geometric shape does a molecule with three bonding pairs and one lone pair form?

Trigonal pyramidal.

For a molecule with four bonding pairs and no lone pairs, what is the electron pair geometry?

Tetrahedral.

What is the difference between bond angles in ideal and actual molecular geometries?

Actual angles can deviate due to lone pairs reducing bond angles.

How do you approach Lewis structures for anions or cations?

Add or subtract electrons based on the charge while summarizing total valence electrons.

What is the significance of observability in VSEPR theory?

It determines molecular shape based on electron density, not wavefunctions.

What do you analyze to compare BF3 and NO2 in terms of molecular geometry?

Their electron pair geometries and molecular shapes.

What is the standard method for calculating formal charges in Lewis structures?

Using valence electron counts minus unshared and half of shared electron counts.

What is the relationship between the octet rule and chemical stability?

Atoms form bonds to achieve full valence electron shells, promoting stability.

When can the octet rule be violated?

In cases of radicals, and with elements like Be, B, and hypervalent species.

What are the bond angles typically associated with corners in a trigonal bipyramidal geometry?

90° and 120°.

What happens when you increase the number of lone pairs in a molecular structure?

Lone pairs take up more space and push bonded atoms closer together.

How do informal practices in Lewis structure assignments help in molecular prediction?

They allow for intuitive assessments based on oxidation states and bonding preferences.

What general characteristics define organic compounds' bonding?

Carbon typically forms four bonds and follows specific bonding rules with other elements.

How can formal charge help in determining the best Lewis structure?

It highlights the most stable arrangement based on charge minimization.

What is a practical application of understanding molecular shape and polarity?

It aids in predicting chemical reactivity and interactions with other substances.

What is the main limitation of the Lewis Theory?

Does not provide information about molecular geometry or why bonds form.

What is the relationship between molecular shape and polarity?

The shape affects whether the molecule is polar or nonpolar.