Unit 2: Section 3 - period 3 elements CDS *

Question 1

why is sodium more reactive than magnesium?

Answer 1

it only has to lose 1 electron to form an ion whereas magnesium loses 2.
so it requires less energy

Question 2

what happens when sodium reacts with water?

Answer 2

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)

Question 3

what happens when magnesium reacts with cold water?

Answer 3

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)

Question 4

what happens when magnesium reacts with steam?

Answer 4

reacts much faster than with cold water, forming magnesium oxide
Mg(s) +2H2O(g) –> MgO(s) +H2(g)

Question 5

what happens when period 3 elements react with oxygen?

Answer 5

they form oxides

usually oxidised to their highest oxidation state = the same as their group numbers. except sulfur which forms SO2

Question 6

what is the reaction between oxygen and sodium?

Answer 6

2Na(s) + 1/2O2(g) –> Na2O(s)

vigorous reaction in air

Question 7

what is the reaction between oxygen and aluminium?

Answer 7

2Al(s) + 3/2O2(g) –> Al2O3(s)

slow reaction in air

Question 8

what is the reaction between oxygen and phosphorus(V)?

Answer 8

P4(s) + 5O2(g) –> P4O10(s)

spontaneously combusts in air

Question 9

what is the reaction between oxygen and magnesium?

Answer 9

Mg(s) + 1/2O2(g) –> MgO(s)

vigorous reaction in air

Question 10

what is the reaction between oxygen and silicon?

Answer 10

Si(s) + O2(g) –> SiO2(s)

slow reaction in air

Question 11

what is the reaction between oxygen and sulfur?

Answer 11

S(s) + O2(g) –> SO2(s)

burns steadily in air

Question 12

what is the bonding of the period 3 oxides?

Answer 12

giant ionic lattice - Na2O, MgO, Al2O3
giant covalent lattice - SiO2
simple covalent molecule - P4O10, SO2

Question 13

why do the ionic period 3 oxides have high melting points?

Answer 13

they form giant ionic lattices

strong FOA between each ion means lots of energy is required to break the bonds to melt them

Question 14

why does magnesium oxide have the highest melting point?

Answer 14

MgO has higher melting point than Na2O because Mg forms 2+ ions, so bonds more strongly than the 1+ Na ions in Na2O

Question 15

why does aluminium oxide have the second highest melting point?

Answer 15

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

Question 16

why does SiO2 have such a high melting point?

Answer 16

it has a giant macromolecular structure

lots of energy needed to break strong covalent bonds between atoms

Question 17

why do P4O10 and SO2 have such low melting points?

Answer 17

they form simple molecular structures

molecules bound by weak intermolecular forces which take little energy to break

Question 18

what happens when ionic oxides of Na and Mg dissolve in water?

Answer 18

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

Question 19

what happens when simple covalent oxides of phosphorus and sulfur dissolve in water?

Answer 19

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

Question 20

what happens when the giant covalent structure of silicon dioxide is added to water?

Answer 20

it is insoluble in water.

it will react with bases to form salts so is classed as acidic

Question 21

what happens when aluminium oxide reacts with water?

Answer 21

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

Question 22

what is the general reaction between acids and bases?

Answer 22

acid + base –> salt + water

Question 23

what is the acid-base reaction for sodium oxide?

Answer 23

Na2O(s) + 2HCl(aq) –> 2NaCl(aq) + H2O(l)

Na2O(s) + H2SO4(aq) –> Na2SO4(aq) + H2O(l)

Question 24

what is the acid-base reaction for magnesium oxide?

Answer 24

MgO(s) + H2SO4(aq) –> MgSO4(aq) + H2O(l)

3MgO + 2H3PO4 —-> 3H2O + Mg3(PO4)2

Question 25

what is the acid-base reaction for silicon dioxide?

Answer 25

SiO2(s) + 2NaOH(aq) –> Na2SiO3(aq) + H2O(l)

it must be hot and concentrated

Question 26

what is the acid-base reaction for P4O10?

Answer 26

P4O10(s) + 12NaOH(aq) –> 4Na3PO4(aq) + 6H2O(l)

Question 27

what is the acid-base reaction for sulfur dioxide?

Answer 27

SO2(s) + 2NaOH(aq) –> Na2SO3(aq) + H2O(l)

Question 28

what is the acid-base reaction for SO3?

Answer 28

SO3(s) + 2NaOH(aq) –> Na2SO4(aq) + H2O(l)

Question 29

what is the acid-base reaction for aluminium oxide?

Answer 29

with acids
Al2O3(s) + 3H2SO4(aq) –> Al2(SO4)3(aq) + 3H2O(l)
with bases
Al2O3(s) + 2NaOH(aq) –> 3H2O(l) + 2NaAl(OH)4(aq)