Please answer and explain!
1) How many total valence electrons are on the silicate (SiO3 2-) ion?
2) How many lone pairs are on the entire structure for the correct Lewis structure of carbon dioxide?
3) What is the electron geometry of a molecule with two bonding domains and three pairs of electrons on the central atom?
The Correct Answer and Explanation is :
1) How many total valence electrons are on the silicate (SiO₃²⁻) ion?
The silicate ion, ( \text{SiO}_3^{2-} ), consists of a silicon (Si) atom and three oxygen (O) atoms with a 2- charge. Here’s how to calculate the total number of valence electrons:
- Silicon (Si) is in group 14 of the periodic table, so it has 4 valence electrons.
- Oxygen (O) is in group 16, so each oxygen atom has 6 valence electrons. Since there are 3 oxygen atoms, this gives ( 6 \times 3 = 18 ) valence electrons.
- The 2- charge on the ion means the ion has gained 2 extra electrons.
Total valence electrons:
[
\text{Valence electrons} = 4 (\text{from Si}) + 18 (\text{from O}) + 2 (\text{charge}) = 24 \text{ electrons}
]
Thus, the silicate ion ( \text{SiO}_3^{2-} ) has 24 valence electrons in total.
2) How many lone pairs are on the entire structure for the correct Lewis structure of carbon dioxide (CO₂)?
Carbon dioxide (CO₂) has a central carbon atom double-bonded to two oxygen atoms. Here’s the process to determine the lone pairs:
- Valence electrons in CO₂:
- Carbon (C) is in group 14, so it has 4 valence electrons.
- Each oxygen (O) is in group 16, so each has 6 valence electrons. There are two oxygens, so ( 6 \times 2 = 12 ) valence electrons from oxygen.
Total valence electrons = 4 (from C) + 12 (from O) = 16 valence electrons.
- Drawing the Lewis structure:
- Carbon is the central atom, and each oxygen is double-bonded to carbon. Each double bond uses 4 electrons, 2 for each bond.
- The remaining electrons are placed as lone pairs on the oxygen atoms.
After forming the double bonds, there are 4 electrons left for the oxygen atoms (2 electrons for each lone pair). Thus, each oxygen atom will have 2 lone pairs.
- Counting lone pairs:
- Each oxygen has 2 lone pairs.
- Since there are two oxygens, this gives ( 2 \times 2 = 4 ) lone pairs in total.
Thus, the correct number of lone pairs in the entire structure of CO₂ is 4 lone pairs (2 on each oxygen atom).
3) What is the electron geometry of a molecule with two bonding domains and three pairs of electrons on the central atom?
In a molecule with two bonding domains and three pairs of electrons on the central atom, the total number of electron pairs around the central atom is five (2 bonding + 3 lone pairs). This corresponds to a trigonal bipyramidal electron geometry.
Explanation:
- Electron Geometry:
- The electron geometry is determined by the total number of electron pairs around the central atom, both bonding and lone pairs.
- For 5 electron pairs, the electron geometry is trigonal bipyramidal. In this geometry, the central atom is surrounded by 5 positions: 3 in a plane (equatorial positions) and 2 above and below the plane (axial positions).
- Molecular Shape:
- The bonding domains are the regions where atoms are bonded. In this case, there are 2 bonding domains (from the 2 bonds).
- The lone pairs occupy positions that minimize electron repulsion. Lone pairs preferentially occupy the equatorial positions (the plane) because they experience less repulsion compared to the axial positions.
- Electron Pair Arrangement:
- With 3 lone pairs and 2 bonding domains, the lone pairs will occupy 3 of the 5 positions (preferably the equatorial positions), and the bonding pairs will occupy the remaining 2 positions.
- Although the molecular geometry (the arrangement of atoms) may differ based on the number of lone pairs, the electron geometry remains trigonal bipyramidal due to the total number of electron pairs being 5.
Thus, the electron geometry of the molecule is trigonal bipyramidal.
This geometry results in a less symmetrical molecular shape, such as linear if only 2 atoms are bonded (depending on how the bonding pairs are oriented). The lone pairs cause deviations from the ideal bonding angles.