AS/A-Level Chemistry- Periodicity applications

Let's see some questions to consolidate your knowledge on A-Level Chemistry periodicity!

1. Explain why Cl has a greater electronegativity than Na

• Cl has a greater number of protons, greater nuclear charge than Na
• Cl has a smaller size, greater charge density than Na
• Cl has similar shielding to Na
• Cl attracts the bonding pair of electrons to the nucleus more

2. Explain why Mg has a higher boiling point than Na

• Mg²⁺ion has a greater charge, greater charge density than Na⁺ion
• Stronger electrostatic forces of attraction between positively-charged Mg²⁺ions and the negatively-charged sea of delocalised electrons, stronger metallic bonding between positively-charged Mg²⁺ions and the negatively-charged sea of delocalised electrons
• More energy required to break the stronger metallic bonding 

3. State the equations and observations for the reactions of Na, Mg, Al, Si, P and S with oxygen

• 4Na + O₂ ⇨ Na₂O
• Vigorous exothermic reaction, yellow flame, white solid
• 2Mg + O₂ ⇨  2MgO
• Vigorous exothermic reaction, white flame, white solid powder
• 4Al + 3O₂ ⇨ 2Al₂O₃
• White flame, white solid powder
• Si + O₂ ⇨SiO₂
• White flame, white solid powder
• 4P + 5O₂ ⇨ P₄O₁₀
• Vigorous exothermic reaction, white flame, white solid powder
• S + O₂ ⇨ SO₂
• Blue flame, colourless gas, choking gas fumes

4. Explain why MgO has a higher melting point and boiling point than MgCl₂ and Li₂O has a higher melting point and boiling point than Na₂O

• O^_2-has a greater charge density than Cl^- ion
• there are stronger electrostatic forces of attraction between oppositely-charged ions, O^2-and Mg²⁺ions, stronger ionic bonds between oppositely-charged ions, O^2- and Mg²⁺ions
• Li⁺ ion is smaller than the Na⁺ ion
• there are stronger electrostatic forces of attraction between oppositely-charged ions, Li⁺ and O^2-ions, stronger ionic bonds between oppositely-charged ions, Li⁺and O^2- ions

5. State the link between electronegativity and the type of bonding and explain whether Na₂O or P₄O₁₀ has a higher melting point in terms of the types of bonding and structures

• P₄O₁₀: Small difference in electronegativity, more covalent character, less ionic character
• Na₂O: Big difference in electronegativity, more ionic character, less covalent character
• Na₂O has ionic bonding and a giant ionic lattice structure
• strong electrostatic forces of attraction and strong ionic bonds between oppositely-charge ions between oppositely-charged ions, Na⁺and O^2-ions
• P₄O₁₀has covalent bonding between P and O atoms and a simple molecular structure
• Weak van der Waals forces between molecules
• Therefore Na₂O has a greater melting point than P₄O₁₀

6. Explain why Al₂O₃is not soluble in water

• Ionic bonding with additional covalent character
• Al³⁺ ion has a small size, can get close to the O^2-ion
• Al³⁺ ion has a high charge density
• Al³⁺ ion has high electronegativity
• Al³⁺ ion polarises the O^2- ion, distorts the O^2- ion electron cloud

7. Explain how Na₂O reacts with water to form an alkaline solution and suggest why Na₂O should not be added in excess for neutralisation of a lake whereas MgO can be added in excess for neutralisation of a lake

• O^2- ion reacts with water, accepts a proton
• Forms OH^- ions, produces NaOH
• Excess NaOH would make the lake alkaline, kill wildlife
• MgO is sparingly soluble, would make the lake weakly alkaline

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Drafted by Eunice Wong (Chemistry)

References: 

https://gph.is/g/E1651mr