Explain the trend in electronegativities across Period 3
- Electronegativitiy is the ability of an atom to attract a bonding pair of electron
- Electronegativity increases across period
- Proton number increases so increase in nuclear charge
- Same number of electron shells so constant shielding
- Attraction of bond pair to nucleus increases
Using electronegativity, why does Na2O and P4O10 have different melting points
- When there’s a big difference in electronegativity, ionic bonding occurs
- Smaller difference is covalent bond
- Na2O is an ionic lattice
- Strong elec forces of attraction between opp-charged ions
- P4O10 is a simple covalent molecule
- There are weak intermolecular forces between molecules
- melting point Na2O greater than for P4O10
Explain the high mp of SiO2 and why is it insoluble
- Macromolecule
- Many strong covalent bonds to be broken
- lots of energy required to break bond
- Water cannot supply enough energy to break the covalent bonds
Observations when Mg burns in O2 and when the oxide is added to water
- Bright White flame
- White Solid formed
- pH 10
- MgO + H2O → Mg(OH)2
Observations when Na burns in O2 and when the oxide is added to water
- Yellow flame
- White solid formed
- vigorous reaction;
- forms a colourless solution;
- pH of solution formed = 13/14;
- Na2O + H2O → 2NaOH;
Observations when Al burns in O2 and when the oxide is added to water
- Normal flame
- The layer of Al2O3 is insoluble
- No reaction pH 7
Observations when P burns in O2 and when the oxide is added to water
- White flame
- Clouds of white smoke is formed
- vigorous reaction;
- forms a colourless solution;
- pH of solution formed = 0 or 1;
P4O10 + 6H2O →¨ 4H3PO4;
Observations when S burns in O2 and when the oxide is added to water
- Blue flame
- Smelly and choking gas made
- SO2 + H2O → H2SO3 pH (0-2)
Explain why sodium oxide reacts to form an alkaline solution when added to water and state what is observed
- O2– accepts a proton forming OH– ions
- NaOH is formed
- O2– + H2O→ 2OH– (2m)
How can we prove a metal oxide something has ions
- heat until molten
- if molten oxide conducts electricity its ionic
Why does Na2O have a high mp
- Ionic lattice
- Strong electrostatic forces of attraction between ions
- A lot of energy needed to break the ionic forces
Why does SO2 have a low mp?
- Simple Molecular structure
- Weak van der Waals forces between molecules
- Little energy needed to break them
Why does P4O10 have a higher mp than SO2?
- P4O10 bigger molecule (Mr) than SO2
- Both simple molecular
- The van der Waals forces between molecules stronger
Structure of P4O10 and explain the low mp
- simple covalent molecule (2m)
- weak van der Waals forces between molecules
- low energy needed to break van der Waals forces
Write 2 equations to show the amphoteric nature of Al
- Al(OH)3 + OH- → Al(OH)4- (acidic)
- Al(OH)3 + 3H+ + 3H2O → Al(H2O)6 3+ (basic)
e.G
- Al(OH)3 + NaOH ⇒ NaAl(OH)4
- 2Al(OH)3 + 3H2SO4 ⇒ Al2(SO4)3 + 6H2O
Why is Al(OH)3 insoluble
- ΔG is +ve for the reaction
- Sum of the hydration enthalpies is less than that of the covalent bond energies
Explain the pattern of conductivity of Na2O
- Can’t conduct when solid as ions can’t move in a solid state
- When molten or in solution, the ions are free to move
Simple chemical test to show that Na2O is present
- Add water, NaOH forms
- Test pH
- pH should be 13/14
Why is SiO2 classed as an acidic oxide?
Reacts with bases, neutralising them
CaO + SiO2 →CaSiO3
Write ionic equations to show the reaction of Cr(OH)3 with HCl and NaOH
Cr(OH)3 + 3H2O + 3H+ → [Cr(H2O)6] 3+
Cr(OH)3 + 2H2O + OH– → [Cr(OH)6]<span>3-</span>
Why is the mp of Mg greater than Na
- Mg2+ has a greater charge density than Na+
- Attracts sea of electrons more strongly
- Mg has more delocalised electrons per Mg2+ ion
- Metallic bonding stronger
