Period 3

Question 1

Atomic radii

Answer 1

Decreases across a period

Question 2

Ionic radii

Answer 2

Decreases across the period

Question 3

Melting points of the elements

Answer 3

Increases across the metal elements of the period

Negligible for non-metal elements

Question 4

Simple molecular

Answer 4

No free electrons
No electrical conductivity
Low melting points as only Van der Waals forces to overcome

Question 5

Giant molecular

Answer 5

No free electrons
No electrical conductivity
High melting points as strong covalent bonds

Question 6

Metallic bonding

Answer 6

Free electrons
Electrical conductivity
High melting points as strong electrostatic forces of attraction

Question 7

First ionisation energy

Answer 7

Amount of energy needed to remove electrons

First ionisation energy increase across the period

Question 8

Magnesium oxide used to

Answer 8

Line furnaces

Question 9

Aluminium oxide used to

Answer 9

Make ceramics
Withstands high temperatures and provides electrical insulation
Same as silicon dioxide

Question 10

Sodium plus oxygen

Answer 10

Sodium oxide (Na2O)
Yellow flame
Produces white solid
Basic

Question 11

Magnesium plus oxygen

Answer 11

Magnesium oxide (MgO)
Burns with white flame
Produce white solid
Basic

Question 12

Aluminium plus oxygen

Answer 12

Aluminium oxide (Al2O3)
White flame
Produces white solid
Amphoteric

Question 13

Phosphorus plus oxygen

Answer 13

Phosphorus oxide (P4O10)
White flame
Produces white solid
Acidic

Question 14

Sulfur plus oxygen

Answer 14

Sulfur dioxide (SO2) 
Sulfur trioxide (SO3)
Blue flame
Produces colourless gas
Acidic

Question 15

Sodium plus chlorine

Answer 15

Sodium chloride (NaCl)
Orange flame

Question 16

atomic and ionic radius of period 3 element

Answer 16

• atomic: DECREASES across because nuclear charge increases with no extra shielding
• ionic:
- metals = smaller
- non metals = bigger

Question 17

electrical conductivity of period 3 elements

Answer 17

overall decrease

metals with metallic bonding —> non metals with covalent bonding —> Ar which is monatomic

Question 18

melting point of period 3 elements

Answer 18

general decrease, silicon has highest melting point due to covalent bonds in a giant 3D molecular structure

Question 19

describe the reactions of period 3 elements with oxygen

Answer 19

• reactivity with oxygen generally decreases
• Ar doesn’t react, Cl doesn’t combine with O2 directly
• metals have an oxide layer
• Na is stored under oil to prevent reaction, P is stored under H2O

Question 20

describe the reaction of the period 3 oxides with water

Answer 20

• metal oxides = basic and give metal hydroxide
• non metal oxides = acidic so give an acid
• Al2O3 is amphoteric, SiO2 is neutral so no reaction

Question 21

describe the oxidation number of the oxides

Answer 21

• most elements burn to form oxide containing element in its highest oxidation state
• sulfur is an exception - in SO2 = +4, in SO3 = +6

Question 22

describe the reaction of period 3 elements with chlorine

Answer 22

• reactivity decreases
• Mg = vigorous when heated, Al = vigorous when heated under anhydrous conditions
• Si & P = slow

Question 23

describe the reaction of period 3 chlorides with water

Answer 23

• Na & Mg Cl dissolve in water to form neutral solutions (Mg is slightly acidic)
• PCl5 releases fumes of HCl and phosphoric acid (violent)
• Aluminium chloride releases fumes of HCl