Molecular structure and bonding flashcards

Molecular structure and bonding covers how atoms connect and arrange themselves in molecules. Students must understand Lewis structures, including how to assign formal charges and draw resonance structures. VSEPR theory explains how electron domains around a central atom determine both electron geometry and molecular geometry, which in turn affects polarity. Bond polarity arises from electronegativity differences, and molecular polarity depends on both bond polarity and geometry. Valence bond theory introduces sigma and pi bonds, and hybridization (sp, sp2, sp3, sp3d, sp3d2) explains observed molecular shapes. Students should connect hybridization to bond angles and geometry. Understanding how bonding type and molecular shape influence physical properties such as boiling point and solubility is also essential for the AP exam.

1. Card 1

   What is a Lewis structure and what does it show?

   A Lewis structure is a diagram showing all valence electrons in a molecule, including bonding pairs and lone pairs, revealing connectivity and electron distribution.

2. Card 2

   How do you calculate formal charge on an atom in a Lewis structure?

   Formal charge = valence electrons minus lone pair electrons minus half the bonding electrons. The most stable structure minimizes formal charges.

3. Card 3

   What are resonance structures and why are they used?

   Resonance structures are multiple valid Lewis structures for one molecule. The actual structure is a resonance hybrid, with electron density spread across all contributing structures.

4. Card 4

   What is the core idea behind VSEPR theory?

   VSEPR theory states that electron domains around a central atom repel each other and arrange to minimize repulsion, determining the molecule's electron geometry.

5. Card 5

   What is the difference between electron geometry and molecular geometry?

   Electron geometry includes all electron domains (bonding and lone pairs); molecular geometry describes only the positions of atoms, ignoring lone pairs.

6. Card 6

   How do lone pairs affect bond angles compared to bonding pairs?

   Lone pairs exert greater repulsion than bonding pairs, compressing bond angles. For example, water's H-O-H angle is about 104.5 degrees, less than the ideal 109.5 degrees.

7. Card 7

   What makes a bond polar, and what makes a molecule polar?

   A polar bond forms when atoms differ in electronegativity. A polar molecule results when polar bonds do not cancel due to asymmetric molecular geometry.

8. Card 8

   What is a sigma bond and how does it form?

   A sigma bond forms by head-on overlap of orbitals along the internuclear axis. It is the first bond formed between two atoms and allows free rotation.

9. Card 9

   What is a pi bond and how does it differ from a sigma bond?

   A pi bond forms by side-by-side overlap of p orbitals above and below the internuclear axis. Double bonds contain one sigma and one pi bond; triple bonds contain one sigma and two pi bonds.

10. Card 10

    What hybridization corresponds to a tetrahedral electron geometry?

    sp3 hybridization produces four equivalent hybrid orbitals arranged tetrahedrally with bond angles of 109.5 degrees, as seen in methane (CH4).

11. Card 11

    What hybridization and geometry does a molecule with two bonding domains have?

    Two bonding domains give sp hybridization with a linear geometry and bond angles of 180 degrees, as in CO2 or BeCl2.

12. Card 12

    How does molecular polarity influence intermolecular forces and physical properties?

    Polar molecules experience dipole-dipole forces and have higher boiling points than nonpolar molecules of similar mass, which only have London dispersion forces.

• Students often confuse electron geometry with molecular geometry, forgetting that lone pairs count as electron domains for shape determination but are not included when naming the molecular geometry.
• A common error is assuming that any molecule with polar bonds must be polar overall, overlooking how symmetrical arrangements such as in CO2 or CCl4 cause bond dipoles to cancel.
• Students frequently misassign hybridization by counting only bonding pairs around the central atom instead of all electron domains, including lone pairs, leading to incorrect hybrid orbital labels.

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