I tried these examples with my classes this year. They are all mistakes I have seen students make in exams. Some of them are obviously wrong and others are more subtly wrong.
So can you work out what is wrong with the following explanations?
- Calcium has a higher melting point than Barium because there are stronger intermolecular forces between its atoms
- PH3 has covalent bonding because phosphorus has a small electronegativity
- Methane has a low boiling point because it has weak van der waals between its atoms
- Ammonia (NH3) has a trigonal planar shape because it has 3 bond pairs trying to get as far as way as possible from each other
- A metallic bond in an element is the electrostatic force of attraction between its nucleus and its delocalised electrons
- CH4 has a tetrahedral shape as the four hydrogen atoms try to repel as far away from each other as possible
- Water has a higher boiling point than H2S because it can form hydrogen bonds between its O and H atoms
- NaF has a higher melting point than NaBr as fluorine is a smaller atom and so has stronger bonding between its atoms
- CO2 is a gas because it has weak covalent bonds
- CCl4 is a non-polar molecule because there is no electronegativity difference between C and Cl
- NaCl can dissolve in water because it can hydrogen bond with water
- Sodium chloride can conduct electricity when molten because it has free electrons.