VSEPR Theory Quiz

A molecule with two bond pairs and no lone pairs adopts a linear shape according to VSEPR theory. This is because the bond pairs arrange themselves as far apart as possible to minimize repulsion, resulting in a 180-degree angle between them. The linear configuration is the most energetically favorable arrangement for two bonding electron pairs around a central atom, allowing for maximal spatial separation and minimal repulsive interaction.

VSEPR theory, or Valence Shell Electron Pair Repulsion theory, explains the three-dimensional shape of molecules. It states that electron pairs around a central atom will arrange themselves as far apart as possible to minimize repulsion between them. This spatial arrangement of electron pairs, both bonding and non-bonding (lone pairs), determines the overall geometry of the molecule, influencing molecular properties and reactivity.

A molecule with three bond pairs and no lone pairs exhibits a trigonal planar geometry. In this arrangement, electron pairs are spaced evenly around the central atom in a plane, creating 120-degree angles between each bond. This configuration allows for the electron pairs to be as far apart as possible, reducing repulsion and stabilizing the molecule.

According to VSEPR theory, the molecular shape of a molecule is determined by the arrangements of electron pairs around the central atom. These electron pairs include both bonding pairs, which form bonds between atoms, and lone pairs, which are unbonded. The theory posits that electron pairs will position themselves as far apart as possible to minimize repulsion, thus dictating the molecule’s overall geometry.

A water molecule (H₂O) is predicted by VSEPR theory to have a bent shape. This is due to its two hydrogen atoms and two lone pairs on the oxygen atom. The lone pairs are located closer to each other and to the oxygen nucleus, resulting in greater repulsion compared to the hydrogen-oxygen bonds. This repulsion between the lone pairs forces the molecule into a bent shape, rather than a linear or tetrahedral one, with an approximate bond angle of 104.5 degrees.

In VSEPR theory, lone pairs of electrons tend to repel each other more strongly than bonding pairs due to their closer proximity to the nucleus and lack of bonding constraint. This increased repulsion influences molecular geometry by pushing bonding electron pairs closer together, often resulting in adjustments to the ideal bond angles and causing deviations from expected molecular shapes. This behavior is crucial for understanding the three-dimensional structure of molecules.

In a tetrahedral molecular geometry, the bond angles are about 109.5 degrees. This shape is formed when four electron groups surround a central atom, arranging themselves to maximize distance between each pair due to repulsion. The tetrahedral geometry ensures that each bond angle is identical and the arrangement is symmetric, minimizing the potential for electron pair repulsion across all adjacent pairs.

A trigonal bipyramidal shape involves five electron groups around the central atom, consistent with VSEPR theory which dictates that such an arrangement minimizes repulsion among electron pairs. In this geometry, three equatorial positions form a 120-degree angle with each other, while two axial positions align perpendicularly at 90 degrees to the equatorial plane. This configuration allows for effective spatial separation of electron pairs.

A molecule with two bond pairs and two lone pairs typically exhibits a bent shape. In this configuration, the lone pairs occupy positions that force the bonded atoms to come closer, resulting in a bent structure. The repulsion between the larger, more repulsive lone pairs pushes the bonding pairs together, decreasing the bond angle below the typical 109.5 degrees seen in a tetrahedral arrangement to approximately 104.5 degrees.

For a molecule with four bond pairs and one lone pair, the seesaw shape is formed. VSEPR theory dictates that lone pairs occupy more space than bonding pairs, distorting a trigonal bipyramidal arrangement into a seesaw geometry. This allows for the lone pair to exert repulsive forces asymmetrically, affecting the angles and positions of the bonding pairs to create a seesaw configuration, which balances the repulsion between electron pairs optimally.