Period 3 and their oxides Flashcards
State the observations with sodium + water and write the equation
- fizzing, melts to form a ball and floats
- 2Na +2H2O → 2NaOH +H2
State the observations with Magnesium + cold water and write the equation
- very slow, small bubbles of gas after a few days
- forms a weak alkaline solution
- Mg + 2H2O → Mg(OH)2 +H2
Explain why sodium is more reactive than magnesium
- ∵ it takes less energy to lose 1 electron than to lose 2
- ∴ more energy (usually heat) is needed for magnesium to react
State the observations with Magnesium + steam and write the equation
- bright light
- Mg + H2O → MgO + H2
Why is magnesium hydroxide not produced in Magnesium + steam
because Mg(OH)2 decomposes at high temperature
State the observations with chlorine + cold water and write the equation?
- forms a pale green solution (pale green is due to the presence of chlorine)
- equilibrium is established
- Cl2 + H2O = HCl + HCLO
State the observations with chlorine + cold water in the presence of SUNLIGHT and write the equation.
- a colourless gas is formed and the pale green colour fades
Cl2 + 2H2O → 4HCL +O2
Describe the trend across period 3 in the reaction with oxygen
- metal oxides are formed
- all the metals are oxidised to their greatest oxidation state which is the same as their group number
- Na and Mg are both ionic lattices
- Aluminium is ionic but has some covalent character
- Si is macro-molecular and P, S are all molecular
Why is there a degree of covalent bonding with aluminium oxide?
aluminium ion is very small and positively charged and can distort the oxygen’s electron cloud.
State the observations with Sodium + oxygen and write the equation
- 4Na + O2 → 2Na2O
- yellow flame and yellow solid
State the observations with Magnesium + oxygen and write the equation
- 2Mg + O2 → 2MgO
- bright white light and crumbly whitle solid formed
State the observations with Aluminium + oxygen and write the equation
- Bright white light and white flaky powder
- 4Al + 3O2 → 2Al2O3
State the observations with Silicon + oxygen and write the equation
- Si + O2 → SiO2
- reaction gives off light
State the observations with Phosphorus + oxygen and write the equation
- bright white light and white solid
- P4 + 5O2 (g) → P4O10
State the observations with Sulfur + oxygen and write the equation
- blue flame and smelly gas
- S+ O2 → SO2
Describe the trend in melting point of the period 3 oxides and describe how their bonding and structure affects this
- Na2 O, MgO and Al2O3 are metal oxides. They have high melting points because they form giant ionic lattices = strong forces of attraction between oppositely charged ions - a lot of heat energy to break the bonds
- MgO has a higher melting point than Na2O because Mg forms 2+ ions, so bonds more strongly than the 1+ Na ions in Na2O.
- Al2O3 has a lower melting point than you might expect because the highly charged Al3+ ions distort the oxygen’s electron cloud making the bonds partially covalent.
- SiO, has a higher melting point than the other non-metal oxides because it has a giant macromolecular structure = the strong covalent bonds between atoms need to be broken
- P4O10 and SO2 have relatively low melting points because they form simple molecular structures. The molecules are bound by weak intermolecular forces (dipole-dipole and van der Waals), which take little energy to break.
How does sodium oxide and magnesium oxide react with water? Write the equations
- both of these oxides are basic as the oxide ions react with water and accept a proton to from hydroxide ions (O2 - +H2O -> 2OH-)
- Sodium reacts to give a strongly alkaline solution
- Magnesium reacts to give a somewhat alkaline solution
What are the insoluble oxides formed in period 3. Why are they insoluble?
aluminium oxide = very high lattice enthalpy
silicon dioxide = giant covalent so strong covalent bonds would have to be broken
What are the oxides in period 3 that act as acids in the reaction with water? Explain the chemistry behind this and write the equations
phosphorus pentoxide, sulfur dioxide and sulfur trioxide
H2O molecules attack d+ P/S atoms, leading to the release of H+ from the water molecules
What are the conditions for silicon dioxide + alkali? Write the equation
hot concentrated NaOH
Write the equations for how basic oxides neutralise acids
Write the equation for how P4O neutralise base
Write the equations for how S^4+ and S^6+ neutralise bases
Explain why sodium oxide forms an alkaline solution when it reacts with water.
- Sodium oxide contains $O^{2–}$ ions
- These $O^{2–}$ ions react with water forming OH– ions
Explain why sodium oxide forms a solution with a higher pH than the solution formed from magnesium oxide
Magnesium oxide is less soluble than sodium oxide,
- the reaction of magnesium oxide with water will only partially dissociate into its ions, a less alkaline solution than with sodium oxide is formed.
What is the aluminium oxide reaction with acid and bases?
Suggest why silicon dioxide is described as an acidic oxide even though it is
insoluble in water.
SiO2 reacts with bases / NaOH / CaO / CaCO3
