Period 3 Elements and Oxides
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Explain why sodium is more reactive than magnesium
Sodium is in group 1 and magnesium is in group 2. When they react, Na loses 1 electron to form 1+ ion, whereas Mg loses 2 electrons to form 2+ ions. Na is more reactive than Mg as it takes less energy to lose one electron than to lose two. Therefore, more energy is needed for magnesium to react
Describe sodium reacting with cold water Product pH
Reacts vigorously with cold water, forming a molten ball on the surface, fizzing and producing H2 gas. This produces sodium hydroxide, which is a strongly alkaline solution. pH 12-14
Describe magnesium reacting with cold water Product and pH Why is the solution weakly alkaline?
Reacts very slowly with cold water. Forms a weak alkaline solution (pH 9-10) and a thin coating of magnesium hydroxide forms on the surface of the metal. Because magnesium hydroxide is not very soluble in water, so relatively few hydroxide ions are produced
Reaction of magnesium with steam
Mg reacts much faster with steam (ie when there’s more energy) to form magnesium oxide
Period 3 elements and reactivity with oxygen Describe
Most react readily with oxygen. Usually oxidised to their highest oxidation states- same as their group numbers
General Equation for Period 3 Elements reacting with oxygen
Element + Oxygen –> Oxide
Equations for reaction of following period 3 elements with oxygen: Sodium Magnesium Aluminium Silicon Phosphorous Sulfur
2Na + 1/2O2 –> Na2O. Mg + 1/2O2 –> MgO. 2Al + 1 1/2O2 –> Al2O3. Si + O2 –> SiO2. P4 + 5O2 –> P4O10. S + O2 –> SO2
Reaction of Sulfur Dioxide with Oxygen
Forms SO3. Vanadium catalyst needed
Reactivity with air of Period 3 Elements: Na Mg Al Si P S
Vigorous Vigorous Slow Slow Spontaneously combusts Burn steadily
Effect of bonding and structure on the melting point of Na2O , MgO and Al2O3
Metal oxides. High melting points as they form giant ionic lattices. Strong forces of attraction between each ion means it takes a lot of heat energy to break the bonds and melt them
Effect of bonding and structure on the melting point of MgO
Higher melting point than Na2O because Mg forms 2+ ions, so bonds more strongly than 1+ Na ions in Na2O
Effect of bonding and structure on the melting point of Al2O3
Lower melting point due to difference in electronegativity between Al and O isn’t as large as between Mg and O. Means that oxygen ions in Al2O3 don’t attract the electrons in the metal-oxygen bonds as strongly as in MgO. This makes bonds in Al2O3 partially covalent
Effect of bonding and structure on the melting point of SiO2
Higher melting point than the other non-metal oxides. Due to its macromolecular structure. Strong covalent bonds between atoms need to be broken, and this requires a lot of energy
Effect of bonding and structure on the melting point of P4O10 and SO2
Relatively low melting points because they form simple molecular structures. The molecules are bond by weak intermolecular forces (dipole-dipole and van der Waals) which take little energy to break
Describe ionic oxides
Alkaline
Describe covalent oxides
Acidic
Equations for the following oxides forming acids when reacted with water: P4O10 SO2 SO3
P4O10 + 6H2O –> 4H3PO4 SO2 + H2O –> H2SO3 SO3 + H2O –> H2SO4
Solubility of Silicon Dioxide Exception
Macromolecular structure makes it insoluble in water. Will react with bases to form salts so is classed as acidic
Solubility of Aluminium Oxide Classed as and why?
Insoluble in water (as it’s partially ionic and partially covalently bonded). Amphoteric as it will react with acids and bases to form salts
Equation for Neutralisation
Acid + Base –> Salt + Water
Equations of Basic Oxides neutralising acids: Na2O MgO
Na2O + 2HCl –> 2NaCl + H2O. MgO + H2SO4 –> MgSO4 + H2O
Equations of acidic oxides neutralising bases: SiO2 P4O10 SO2 SO3
SiO2 + 2NaOH –> Na2SiO3 + H2O. P4O10 + 12NaOH –> 4Na3PO4 + 6H2O. SO2 + 2NaOH –> Na2SO3 + H2O. SO3 + 2NaOH –> Na2SO4 + H2O
Equations for amphoteric oxides neutralising acids and bases (Al2O3)
Acid: Al2O3 + 3H2SO4 –> Al2(SO4)2 + 3H2O. Base: Al2O3 + 2NaOH + 3H2O –> 2NaAl(OH)4