Period 3

Question 1

Explain the trend in atomic radius and first ionisation energy for period 3

Answer 1

• Decrease in atomic radius; same shielding and increasing nuclear charge
• Increase in ionisation energy; same shielding and increasing nuclear charge

Question 2

Explain the melting point of period 3 in terms of structure and bonding

Answer 2

Increases from Na - Al because charge on the metal ion increases so stronger attraction between metal ions and delocalised electrons, they all also have giant metallic lattice

Si has the highest MP due to its macromolecular structure along with lots of strong covalent bonds

S8>P4>Cl2>Ar
all simple molecular and have VdW which depend on the size of the molecules

Question 3

Describe how does Na and Mg react with water

Answer 3

2Na + 2H2O –> 2NaOH + H2
Vigorous, fizz, pH 13-14

Mg + 2H2O –> Mg(OH)2 + H2
Slow. few bubble produced over a couple days, weak alkali (9-10) due to its being sparingly soluble

Mg + H2O –> MgO + H2
Steam, occurs alot faster due to higher temperature

Question 4

Describe how Na reacts with oxygen

Answer 4

2Na + 1/2 O2 –> Na2O
yellow flame, white solid

Question 5

Describe how Mg reacts with oxygen

Answer 5

2Mg + O2 –> 2MgO
bright white flame and white solid

Question 6

Describe how Al reacts with oxygen

Answer 6

4Al + 3O2 –> 2Al2O3
Powder and heat: white flame
Air: dull and grey(layer of aluminum oxide)

Question 7

Describe how Si reacts with oxygen

Answer 7

Si + O2 –> SiO2
orange flame and pure SiO2 is white solid (will burn in O2 if heated enough)

Question 8

Describe how P reacts with oxygen

Answer 8

P4 + 5O2 –> P4O10
White phosphorous gives white flame and white fumes produced

Question 9

Describe how S reacts with oxygen

Answer 9

S + O2 –> SO2
Pale blue flame, colourless gas, some SO3 produced

Question 10

Describe the trend in melting point of period 3 oxides

Answer 10

Na2O 1548
MgO 3125
Al2O3 2345
SiO2 1883
P4O10 573
SO3 290
SO2 200

The intermolecular bonds in Al2O3 are weaker than the bonds between magnesium oxide. This results in the greater melting point of magnesium oxide in spite of the less covalent character.

Question 11

Describe the reaction for Na2O with water

Answer 11

Na2O + H2O –> 2Na+ + 2OH-
pH 13-14, forms an alkali solution due to it containing O2- ions which react with water to form OH- ions

Question 12

Describe the reaction for MgO with water

Answer 12

MgO + H2O –> Mg(OH)2
sparingly soluble so weakly alkaline pH 9-10

Question 13

Describe the reaction for Al2O3 with water

Answer 13

No reaction, insoluble, pH 7

Question 14

Describe the reaction for SiO2 with water

Answer 14

No reaction, insoluble, pH 7

Question 15

Describe the reaction for P4O10 with water

Answer 15

P4O10 + 6H2O –> 4H3PO4
pH 1-2

Question 16

Describe the reaction for SO2 with water

Answer 16

SO2 + H2O –> H2SO3
pH 2-3

Question 17

Describe the reaction for SO3 with water

Answer 17

SO3 + H2O –> H2SO4
pH 0-1

Question 18

Which are the basic oxides and give an equation?

Answer 18

Na2O + H2SO4 –> Na2SO4 + H2O

MgO + 2HCl –> MgCl2 + H2O

Question 19

Which are the amphoteric oxides and give an equation?

Answer 19

Amphoteric - act as a base or acid

Al2O3 + 6HCl –> 2AlCl3 + 3H2O

Al2O3 + 2NaOH + 3H2O –> 2NaAl(OH)4

Question 20

Which are the acidic oxides and give an equation?

Answer 20

P4O10 + 12NaOH –> 4Na3PO4 + 6H2O
When P4O10 is added to an alkaline solution it reacts with the water present to form H3PO4
(H3PO4 + 3NaOH –> Na3PO4 + 3H2O)

SO2 + 2NaOH –> Na2SO3 + H2O

SiO2 can also neutralise bases:
SiO2 + 2NaOH –> Na2SiO3 + H2O

Question 21

Give an equation for P4O10 reacting with basic oxides

Answer 21

P4O10 + 6Na2O –> 4NA3PO4

P4O10 + 6MgO –> 2Mg3(PO4)2