Unit 2: Section 3 - period 3 elements CDS * Flashcards
period 3 elements and oxides
why is sodium more reactive than magnesium?
it only has to lose 1 electron to form an ion whereas magnesium loses 2.
so it requires less energy
what happens when sodium reacts with water?
it reacts vigorously with cold water, forming a molten ball on the surface, fizzing and producing H2 gas.
sodium hydroxide is produced, creating a strongly alkaline solution
2Na(s) + 2H2O(l) –> 2NaOH(aq) + H2(g)
what happens when magnesium reacts with cold water?
reacts very slowly with cold water. forming weakly alkaline solution and a thin coating of magnesium hydroxide on the surface of the metal.
magnesium hydroxide is not very soluble in water, so few hydroxide ions are produced = weak alkaline
Mg(s) + 2H2O(l) –> Mg(OH)2(aq) +H2(g)
what happens when magnesium reacts with steam?
reacts much faster than with cold water, forming magnesium oxide
Mg(s) +2H2O(g) –> MgO(s) +H2(g)
what happens when period 3 elements react with oxygen?
they form oxides
usually oxidised to their highest oxidation state = the same as their group numbers. except sulfur which forms SO2
what is the reaction between oxygen and sodium?
2Na(s) + 1/2O2(g) –> Na2O(s)
vigorous reaction in air
what is the reaction between oxygen and aluminium?
2Al(s) + 3/2O2(g) –> Al2O3(s)
slow reaction in air
what is the reaction between oxygen and phosphorus(V)?
P4(s) + 5O2(g) –> P4O10(s)
spontaneously combusts in air
what is the reaction between oxygen and magnesium?
Mg(s) + 1/2O2(g) –> MgO(s)
vigorous reaction in air
what is the reaction between oxygen and silicon?
Si(s) + O2(g) –> SiO2(s)
slow reaction in air
what is the reaction between oxygen and sulfur?
S(s) + O2(g) –> SO2(s)
burns steadily in air
what is the bonding of the period 3 oxides?
giant ionic lattice - Na2O, MgO, Al2O3
giant covalent lattice - SiO2
simple covalent molecule - P4O10, SO2
why do the ionic period 3 oxides have high melting points?
they form giant ionic lattices
strong FOA between each ion means lots of energy is required to break the bonds to melt them
why does magnesium oxide have the highest melting point?
MgO has higher melting point than Na2O because Mg forms 2+ ions, so bonds more strongly than the 1+ Na ions in Na2O
why does aluminium oxide have the second highest melting point?
the difference in electronegativity between Al and O is less than that between Mg and O, so don’t attract electrons in metal-oxygen bond as strongly
why does SiO2 have such a high melting point?
it has a giant macromolecular structure
lots of energy needed to break strong covalent bonds between atoms
why do P4O10 and SO2 have such low melting points?
they form simple molecular structures
molecules bound by weak intermolecular forces which take little energy to break
what happens when ionic oxides of Na and Mg dissolve in water?
the O 2- ions accept protons from the water molecules to form hydroxide ions. the solutions are both alkaline, but sodium hydroxide is more soluble in water so forms a more alkaline solution
what happens when simple covalent oxides of phosphorus and sulfur dissolve in water?
they form acidic solutions
all the acids are strong so the pH is 0-2.
they will dissociate in solution, forming hydrogen ions and a negative ion
what happens when the giant covalent structure of silicon dioxide is added to water?
it is insoluble in water.
it will react with bases to form salts so is classed as acidic
what happens when aluminium oxide reacts with water?
it is partially ionic and partially covalent bonded, and insoluble in water
it will react with acids and bases to form salts so is amphoteric
what is the general reaction between acids and bases?
acid + base –> salt + water
what is the acid-base reaction for sodium oxide?
Na2O(s) + 2HCl(aq) –> 2NaCl(aq) + H2O(l)
Na2O(s) + H2SO4(aq) –> Na2SO4(aq) + H2O(l)
what is the acid-base reaction for magnesium oxide?
MgO(s) + H2SO4(aq) –> MgSO4(aq) + H2O(l)
3MgO + 2H3PO4 —-> 3H2O + Mg3(PO4)2
what is the acid-base reaction for silicon dioxide?
SiO2(s) + 2NaOH(aq) –> Na2SiO3(aq) + H2O(l)
it must be hot and concentrated
what is the acid-base reaction for P4O10?
P4O10(s) + 12NaOH(aq) –> 4Na3PO4(aq) + 6H2O(l)
what is the acid-base reaction for sulfur dioxide?
SO2(s) + 2NaOH(aq) –> Na2SO3(aq) + H2O(l)
what is the acid-base reaction for SO3?
SO3(s) + 2NaOH(aq) –> Na2SO4(aq) + H2O(l)
what is the acid-base reaction for aluminium oxide?
with acids
Al2O3(s) + 3H2SO4(aq) –> Al2(SO4)3(aq) + 3H2O(l)
with bases
Al2O3(s) + 2NaOH(aq) –> 3H2O(l) + 2NaAl(OH)4(aq)
