Molecular Geometry and Orbital Hybridization (5B) - Chem & Physics

1. What counts as one electron domain in VSEPR: a single bond, double bond, or triple bond?

   All count as one electron domain each. In VSEPR, any bond, regardless of being single, double, or triple, is treated as a single electron domain due to shared electron density.

2. What is the electron-domain geometry for a central atom with 6 electron domains?

   Octahedral. Six electron domains minimize repulsion by occupying positions at the vertices of an octahedron around the central atom.

3. Which model is used on the MCAT to predict molecular geometry from electron domains?

   VSEPR (Valence Shell Electron Pair Repulsion) theory. VSEPR theory predicts molecular geometry by minimizing repulsion between electron domains around the central atom.

4. What is the molecular geometry for an AX$_3$E$_2$ species (3 bonds, 2 lone pairs) with 5 electron domains?

   T-shaped. AX$_3$E$_2$ places two lone pairs equatorially in trigonal bipyramidal geometry, leaving a T-shaped arrangement of bonds.

5. What is the molecular geometry for an AX$_2$E$_3$ species (2 bonds, 3 lone pairs) with 5 electron domains?

   Linear. In AX$_2$E$_3$, three equatorial lone pairs in trigonal bipyramidal geometry force the two bonds into axial positions, forming linear geometry.

6. What is the molecular geometry for an AX$_4$E species (4 bonds, 1 lone pair) with 5 electron domains?

   Seesaw. In AX$_4$E, the lone pair prefers an equatorial position in trigonal bipyramidal geometry, resulting in a seesaw shape.

7. What is the molecular geometry for an AX$_2$E$_2$ species (2 bonds, 2 lone pairs) around the central atom?

   Bent (angular). AX$_2$E$_2$ has two lone pairs in tetrahedral positions, bending the two bonds into an angular shape with angle less than $109.5^\circ$.

8. Which hybridization matches 2, 3, and 4 electron domains around a central atom, respectively?

   $sp$, $sp^2$, and $sp^3$. Hybridization corresponds to electron domains: $sp$ for linear (2), $sp^2$ for trigonal planar (3), $sp^3$ for tetrahedral (4).

9. What are the ideal bond angles in an octahedral electron-domain geometry?

   $90^\circ$ and $180^\circ$. Octahedral geometry arranges domains at $90^\circ$ for adjacent and $180^\circ$ for opposite positions to minimize repulsion.

10. What is the electron-domain geometry for a central atom with 5 electron domains?

    Trigonal bipyramidal. Five electron domains arrange with three in a plane and two axial to minimize repulsion, forming a trigonal bipyramid.

11. What is the electron-domain geometry for a central atom with 3 electron domains?

    Trigonal planar. Three electron domains arrange in a plane equidistant from each other to minimize repulsion, forming trigonal planar geometry.

12. What is the molecular geometry for an AX$_5$ species with no lone pairs on the central atom?

    Trigonal bipyramidal. AX$_5$ with five bonding domains and no lone pairs adopts the trigonal bipyramidal electron-domain geometry.

13. What is the ideal bond angle for trigonal planar electron-domain geometry?

    $120^\circ$. Trigonal planar geometry spaces three domains equally in a plane, yielding ideal bond angles of $120^\circ$.

14. What is the molecular geometry for an AX$_4$ species with no lone pairs on the central atom?

    Tetrahedral. AX$_4$ has four bonding domains and no lone pairs, resulting in tetrahedral molecular geometry.

15. What is the molecular geometry for an AX$_3$E species (3 bonds, 1 lone pair) around the central atom?

    Trigonal pyramidal. In AX$_3$E, the lone pair occupies one tetrahedral position, distorting the three bonds into a trigonal pyramidal shape.

16. What is the molecular geometry for an AX$_2$ species with no lone pairs on the central atom?

    Linear. AX$_2$ has two bonding domains and no lone pairs, so molecular geometry matches the linear electron-domain geometry.

17. What is the molecular geometry for an AX$_4$E$_2$ species (4 bonds, 2 lone pairs) with 6 electron domains?

    Square planar. AX$_4$E$_2$ positions two lone pairs trans in octahedral geometry, resulting in square planar arrangement of the four bonds.

18. What are the ideal bond angles in trigonal bipyramidal electron-domain geometry?

    $90^\circ$, $120^\circ$, and $180^\circ$. Trigonal bipyramidal geometry has equatorial angles of $120^\circ$, axial-equatorial at $90^\circ$, and axial-axial at $180^\circ$ for minimal repulsion.

19. What is the electron-domain geometry for a central atom with 4 electron domains?

    Tetrahedral. Four electron domains minimize repulsion by arranging at the vertices of a tetrahedron around the central atom.

20. What is the molecular geometry for an AX$_5$E species (5 bonds, 1 lone pair) with 6 electron domains?

    Square pyramidal. In AX$_5$E, the lone pair occupies one octahedral position, distorting the five bonds into a square pyramidal shape.

21. What is the electron-domain geometry for a central atom with 2 electron domains?

    Linear. With 2 electron domains, repulsion is minimized when they are opposite each other, forming a linear arrangement.

22. What is the ideal bond angle for a linear electron-domain geometry?

    $180^\circ$. In linear geometry, the two domains are positioned at opposite ends, resulting in a $180^\circ$ bond angle to minimize repulsion.

23. What is the molecular geometry for an AX$_3$ species with no lone pairs on the central atom?

    Trigonal planar. AX$_3$ features three bonding domains without lone pairs, aligning with trigonal planar electron-domain geometry.

24. What is the molecular geometry for an AX$_6$ species with no lone pairs on the central atom?

    Octahedral. AX$_6$ with six bonding domains and no lone pairs matches the octahedral electron-domain geometry.

25. What is the ideal bond angle for a tetrahedral electron-domain geometry?

    $109.5^\circ$. Tetrahedral geometry positions four domains to maximize separation, resulting in bond angles of $109.5^\circ$.

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