Please note that “geometry” refers to the molecular or ionic geometry. A. What is the electron-pair geometry for Se in SeOF2? Fill in the blank 1 There are lone pair(s) around the central atom, so the geometry of SeOF2 is fill in the blank 3 . B. What is the electron-pair geometry for Xe in XeO4? Fill in the blank 4 There are lone pair(s) around the central atom, so the geometry of XeO4 is fill in the blank 6 .
The Correct Answer and Explanation is:
A.
Electron-pair geometry for Se in SeOF₂: Trigonal bipyramidal
There is 1 lone pair around the central atom, so the geometry of SeOF₂ is see-saw.
B.
Electron-pair geometry for Xe in XeO₄: Tetrahedral
There are 0 lone pairs around the central atom, so the geometry of XeO₄ is tetrahedral.
Explanation
In molecular geometry, the shape of a molecule is determined by the arrangement of electron pairs around the central atom. This includes both bonding electron pairs (shared between atoms) and lone pairs (non-bonding pairs localized on the central atom). The Valence Shell Electron Pair Repulsion (VSEPR) theory helps predict molecular geometry by minimizing repulsions between electron pairs.
A. SeOF₂ (Selenium oxyfluoride):
Selenium (Se) is the central atom. It is bonded to one oxygen atom and two fluorine atoms, making three bonding pairs. Selenium also has one lone pair. That adds up to four regions of electron density. However, because oxygen typically forms a double bond, the total number of electron domains is five: three bonding domains (one O, two F) and one lone pair. According to VSEPR theory, five electron domains give a trigonal bipyramidal electron-pair geometry. The presence of one lone pair distorts this geometry, resulting in a see-saw molecular geometry. Lone pairs occupy equatorial positions to minimize repulsion, pushing the bonded atoms into the see-saw shape.
B. XeO₄ (Xenon tetroxide):
Xenon (Xe) is the central atom bonded to four oxygen atoms. Each oxygen forms a double bond with xenon, making four bonding pairs. Xenon does not have any lone pairs in this molecule. Four electron regions with no lone pairs result in a tetrahedral electron-pair geometry. Since there are no lone pairs to distort the shape, the molecular geometry is also tetrahedral. This is somewhat unusual for a noble gas like xenon, but it is possible due to the involvement of d-orbitals and the ability of xenon to expand its octet.
In conclusion, the shape of a molecule is determined by both the number of electron domains and the presence of lone pairs. These factors lead to different molecular geometries, even when the number of bonding atoms is the same.
