Consider the following polyatomic ion: AsO2-. – Show the full electron configuration for As. – Draw the most correct Lewis structure for AsO2-. – Briefly explain why your Lewis structure is correct. – If the structure is stabilized by resonance, draw at least one of the possible resonance forms. If it is not stabilized by resonance, briefly explain why. – Consider the following molecule: GeBr2. Indicate the bond angles around the central atom. What is the electronic geometry of this molecule? What is its molecular shape? – Does GeBr2 have a dipole moment? Briefly justify your answer.
The Correct Answer and Explanation is:
. Electron Configuration for As (Arsenic):
The atomic number of Arsenic (As) is 33. Its electron configuration is:
As: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p³
This is the full electron configuration for arsenic. The 4s and 4p orbitals are the valence orbitals for As, and they will play a role in bonding.
2. Lewis Structure for AsO₂⁻:
To draw the Lewis structure for the AsO₂⁻ ion:
- Step 1: Count the total valence electrons.
- As (group 15) has 5 valence electrons.
- O (group 16) has 6 valence electrons, and there are 2 oxygens.
- The negative charge indicates 1 extra electron, adding 1 more electron.
- Total electrons = 5 (As) + 6×2 (O) + 1 (negative charge) = 18 electrons.
- Step 2: Place As as the central atom, and arrange the oxygens around it.
- Step 3: Distribute electrons so that each atom (except hydrogen) follows the octet rule (8 electrons in the valence shell). Oxygen atoms will form single bonds with As and will each have lone pairs.
- Step 4: Place remaining electrons as lone pairs on the oxygens.
- Step 5: Minimize formal charges, ensuring that the most electronegative atoms (Oxygen) carry any negative charge.
The structure will look like this:
mathematicaCopyEdit O
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As - O⁻
Where each oxygen has lone pairs, and arsenic has a lone pair. The charge is on one of the oxygen atoms (denoted by the extra electron).
3. Why is this Lewis structure correct?
This Lewis structure follows the rules of electron counting and minimizes formal charges. The oxygen atoms follow the octet rule, and arsenic has a lone pair, which is common for group 15 elements. Additionally, the extra negative charge is placed on one of the oxygens, as it is more electronegative than arsenic. This minimizes formal charges, which is a key principle when drawing Lewis structures.
4. Resonance in AsO₂⁻:
Yes, the structure is stabilized by resonance. In this case, the negative charge can be delocalized over the two oxygen atoms. This leads to the following resonance structures:
mathematicaCopyEdit O O
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As - O⁻ ↔ As = O
In this case, the negative charge alternates between the two oxygen atoms, making the ion more stable.
5. GeBr₂:
- Bond Angles:
The GeBr₂ molecule has linear geometry because the central atom (Ge) has two bonding pairs of electrons (two Br atoms). According to VSEPR theory, the ideal bond angle for a linear molecule is 180°. - Electronic Geometry:
The electronic geometry of GeBr₂ is linear because the central Ge atom has two electron pairs (bonding pairs). - Molecular Shape:
The molecular shape of GeBr₂ is also linear. There are no lone pairs on the central atom, so the shape is determined by the positions of the two Br atoms. - Dipole Moment:
GeBr₂ does not have a dipole moment. Even though Ge and Br have different electronegativities, the molecule is linear, and the dipoles cancel out because they are in opposite directions. This results in a nonpolar molecule.
Summary:
- AsO₂⁻: The Lewis structure places As in the center with single bonds to two oxygens, one of which carries the negative charge. Resonance helps delocalize the charge.
- GeBr₂: The molecule is linear with bond angles of 180°, and no dipole moment due to the symmetric arrangement of the bonds.
