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7. Difference in melting points of phosphorus dichloride (PCl₂) and magnesium chloride (MgCl₂):
- Structure: Phosphorus dichloride is a molecular compound with covalent bonding, existing primarily as discrete molecules held together by weak Van der Waals forces. In contrast, magnesium chloride has a giant ionic lattice structure formed by ionic bonds, where strong electrostatic forces hold the cations and anions together.
- Bonding: The strong ionic bonds in magnesium chloride require much more energy to break (higher melting point) compared to the weaker Van der Waals forces in phosphorus dichloride (lower melting point). Thus, MgCl₂ has a higher melting point than PCl₂.
8. Difference in melting points of oxygen and sulfur:
- Molecular Structure: Oxygen exists as diatomic molecules (O₂) with Van der Waals forces between them. Sulfur, on the other hand, typically forms S₈ molecules (a crown structure) with stronger Van der Waals forces due to a larger molecular size.
- Bonding: The larger size and greater number of atoms in sulfur allow for stronger London dispersion forces. As such, sulfur's melting point is significantly higher than that of oxygen despite both being in group VI.
9. Distinction between covalent bonds and Van der Waals forces in iodine:
- Covalent bonds in iodine (I₂) are the strong bonds formed between the two iodine atoms, resulting from the sharing of a pair of valence electrons. This creates a stable diatomic molecule.
- Van der Waals forces (specifically London dispersion forces) occur between iodine molecules. These are relatively weak intermolecular forces resulting from temporary dipoles due to fluctuations in electron distribution, and they are responsible for the physical state of iodine.
10. Element table analysis: (a) The electronic arrangements based on atomic numbers:
- Element L (Atomic Number 11): 1s² 2s² 2p⁶ 3s¹
- Element M (Atomic Number 13): 1s² 2s² 2p⁶ 3s² 3p¹
- Element Q (Atomic Number 19): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁵
(b) Selection of elements: (i) The most reactive non-metal is element R (Atomic Number 17). (ii) A poor conductor of electricity is element M.
(c) Element R belongs to period 3 of the periodic table.
(d) Element R loses its outermost electron more readily than L due to being a non-metal with higher electronegativity and a tendency to gain electrons instead of losing them. While lithium (L) is a metal that easily loses one electron from its outer shell.
(e) The bonding between elements N (14) and Q (19) can be shown using dots and crosses:
- N: 1s² 2s² 2p⁶ 3s² 3p² (4 valence electrons, use dots)
- Q: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 4p⁴ (7 valence electrons, use crosses)
- When forming a bond, you would show electron sharing accordingly, typically reflecting a covalent bond.
(f) The melting point of element M is higher than that of element L because M has a higher nuclear charge and can form stronger metallic bonds requiring more energy to break.
(g) The reaction between L (likely lithium) and water can be represented by: \[ 2L + 2H₂O → 2L^+ + 2OH^- + H₂ \]
(h) To separate a solid mixture of sulfate of R and lead sulfate, one could use a method such as filtration, where the solubility difference could help in dissolving one and leaving the other as a solid for collection.
11. Electronic arrangements of Y and Z: (a)
- Element Y (Atomic Number 13): 1s² 2s² 2p⁶ 3s² 3p¹
- Element Z (Atomic Number 9): 1s² 2s² 2p⁵
(b) Dot and cross diagram for Y (Al) and Z (F): Y donates its 3rd shell electron and usually forms a positive ion (Al³⁺). F accepts one to form a negative ion (F⁻):
- Y: 3 valence electrons (dots)
- Z: 7 valence electrons (crosses)
- Combine: Show electron transfer with the appropriate representation.
12. Reactivity order and ionic equation: (a) The order of increasing reactivity (most to least): \[ V < S < T < \text{Hydrogen} \]
(b) If both T and V are divalent metals and react to displace V, the ionic equation could be represented as: \[ T^{2+} + V^{2+} → T^{2+} + V^{2+} + \text{other products} \] This could be adjusted to specific ions based on specific properties of T and V.
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