In: Chemistry
1. Which, if any, of the molecules in Exercise 1 had resonance structures? How many resonance structures did each molecule have? 2. Both chlorine and fluorine are represented by a green modeling piece that has 4 holes. Is using the same piece for two different atoms acceptable? Why or why not? 3. List all of the possible geometric structures of a molecule that contains two atoms. 4. Explain why only the lone pairs on the central atom are taken into consideration when predicting molecular shape. What molecules from the lab activity are exceptions to this? Molecule 1: CCl4 Molecule 2: H2 Molecule 3: H2O Molecule 4: CO2 Molecule 5: O2 Molecule 6: H2O2 Molecule 7: CH4 Molecule 8: C2H4 Molecule 9: CH2O Molecule 10: CH3OH Molecule 11: CH3NH2 Molecule 12: NF3 Molecule 13: NH3 Molecule 14: [NH4]+ Molecule 15: [NO2]- Molecule 16: SO2 Molecule 17: OF2 Molecule 18: H2S Molecule 19: SF6 Molecule 20: ICl5
Answer 1
Molecules which show resonance are CO2, NO2- and SO2. Their resonating structures are as below:
Molecule 4: CO2 Molecule 15 NO2 o. O: Molecule 16: SO2
Answer 2
Both can be shown by same color as both Cl and F are halogens and have similar chemical properties.
Both have four electron pairs around them when they form bonds of ions.
Answer 3
A molecule containing two atoms can only have linear geometry.
Answer 4
Lone pairs of central atom are considered because these lone pairs when present, repel another lone pairs as well as bond pairs. According to VSEPR theory, lone pair - lone pair repulsions are severe than lone pair -bond pair repulsions. For example, the geometry of CO2 is linear but that of H2O is bent because of two lone pairs present in oxygen atom of H2O. To provide more space to lone pair, the bond pairs in water come closer and have bent shape.
There are no exceptions to geometry but to bond angle. If the atom other than central atom has lone pairs and is more electronegative than central atom, affects the bond angle of the molecule.
The bond angle is greater in such cases. For example, H2O and OF2, the electronegativity of F is highest. So, to prevent the repulsions between bond pairs and lone pairs of two F atoms in OF2, bond angle is larger.
Another exception is NH3 and NF3.