Periodicity/ Period 3 elements

Question 1

Describe and explain the trends in atomic radius across Period 3 in terms of structure and bonding. [5]

Answer 1

Decreases across the period [1]
Positive charge of nucleus increases as number of protons increase [1]
increased attraction between nucleus and electrons [1]
no real increase in electron shielding [1]
as electrons added to same outer shell [1]

Question 2

Describe and explain the trends in first ionisation energy across Period 3 in terms of structure and bonding. [4]

Answer 2

Increases across the period [1]
Positive charge of nucleus increases as number of protons increase [1]
Increased attraction between nucleus and electrons [1]
No real increase in electron shielding [1]
As electrons added to same outer shell [1]
Harder to remove the electron [1]

Question 3

Explain the trends in melting points of the elements across Period 3 in terms of structure and bonding. [6]

Answer 3

Metallic bonding (Na, Mg, Al) increase melting point across period [1]
Increased positive charge and delocalised electrons [1]
Macromolecule Si very high melting point [1] 
strong covalent bonds [1]
Molecules and atoms (P, S, Cl, Ar) low melting points [1] weak van der Waals forces [1]

Question 4

Explain why aluminium and sulfur do not follow the overall trend in ionisation energy across Period 3. [4]

Answer 4

Aluminium outer electron 3p/ more distant [1]
additional electron shielding [1]
lower first ionisation energy, easier to remove electron [1]
Sulfur electron being removed is one of a pair [1], electron repulsion, easier to remove electron [1]

Question 5

Explain why the oxides of the Period 3 elements sodium and phosphorus have different
melting points. In your answer you should discuss the structure of and bonding in
these oxides, and the link between electronegativity and the type of bonding.

Answer 5

• big different in electronegativity, smaller difference covalent (1)
  Na2O (sodium oxide):
• metal bonding
• forms ionic lattice (1)
• strong forces of attraction between ions (1)

P4O10 (phosphorus(V) oxide)

• covalent molecular (1)
• weak IM forces between molecules(1)

melting point Na2O greater than P4O10 (1)

Question 6

Predict whether the melting point of lithium oxide is higher than, the same as, or lower
than the melting point of sodium oxide and explain your prediction

Answer 6

• higher (1)
• Li+ smaller than Na+ (1)
• attracts O2- ions more strongly (1)

Question 7

Suggest one reason why a thin layer of aluminium oxide protects aluminium from
corrosion in moist air (1)

Answer 7

• insoluble in water (1)

Question 8

Phosphorus(V) oxide has a lower melting point than sodium oxide. State the structure of and bonding in phosphorus(V) oxide

Answer 8

• simple molecular (1)

- covalent bonds between P and O

Question 9

Write an equation for the reaction between Na2O and P4O10

State the general type of reaction illustrated by this example

Answer 9

Equation: 6Na2O + P4O10 4Na3PO4

Reaction type: Acid-Base