Chem Bonding (JC) Flashcards
Explain why MgO has a higher lattice energy than NaCl
Charges of Mg2+ and O2- ions are higher than Na+ and Cl- respectively
Ionic radii of Mg2+ and O2- are smaller than that of Na+ and Cl- respectively.
Hence, electrostatic forces of attraction between Mg2+ and O2- is higher than the elctrostatic forces of attraction between Na+ and Cl-, resulting in higher lattice energy.
Define Lattice Energy
Lattice energy is the energy released when one mole of the solid ionic compound is formed from the constituent gaseous ions under standard conditions.
What is the metallic bond strength affected by?
- Charge and ionic radius: The greater the charge, the smaller the size of the cation, which results in stronger electrostatic forces of attraction for the delocalised valence electron.
- Number of valence electrons: The larger the number of valence electrons, the greater the charge of the resultant metal cation, and the larger the number of delocalised valence electrons contributed to the sea of electrons. This results in stronger electrostatic forces of attraction for the delocalised valence electron by the metal cations,
Why are elements like P and S able to expand their octet structure?
The central P or S atom can accommodate more than 8 electrons in its valence shell due to the presence of vacant, energetically accessible d orbitals.
Why is a sigma bond stronger than a pi bond
Due to the more extensive overlap of orbitals in a sigma bond compared to a pi bond, a sigma bond is stronger compared to a pi bond.
Why is the melting point of Mg higher than that of Na
Mg and Na have giant ionic lattice structure. Mg2+ has a higher charge and a smaller radius compared to Na+. Mg has more valence electrons than Na. More energy is required to overcome the stronger electrostatic forces of attraction between the Mg2+ ions and the sea of delocalised valence electrons than that of the attraction between Na+ ions and the seas of delocalised valence electrons.
Why does CO2 have low melting points ?
A small amount of energy is required to overcome the weak instantaneous dipole induced dipole interactions between the discrete CO2 molecules.
Why does melting points of alkanes increases down the homologous series?
Alkanes have a simple covalent structure and are held by weak instantaneous dipole induced dipole interactions between the discrete molecules. The strength of id-id increases as the number of electrons in the molecules increases, requiring more energy to be overcome.
Why does a straight-chain isomer have a higher boiling point than a branched isomer of the same formula?
The straight-chain isomer has larger surface area to form more extensive instantaneous dipole induced dipole interactions which requires more energy to be overcome.
Why does H2O have a higher boiling point than H2S
More energy is required to overcome the stronger hydrogen bonds between the discrete H2O molecules compared to the weaker permanent dipole induced dipole interactions between he H2S molecule
Why does H2O have a higher boiling point than HF
More energy is required to overcome the more extensive hydrogen bonds between H2O molecules than that of H2F molecules. Each H2O molecules can potentially form more hydrogen bonds with surrounding H2O molecules compared to each HF molecules with its surrounding HF molecules.
Explain why AlCl3 is covalent
Al3+ has a high charge densituy and high polarising power. Cl- has a big and has a large electron cloud, making it more polarisable. Hence, electron density on Cl- ion is more largely shared with the Al3+.
