Chapter 6: Period 3

Periodic Table

  • In the Periodic Table, elements are arranged in order of increasing atomic number
  • Elements can be grouped into periods (horizontal rows) and groups (vertical columns).
  • Periodicity is a regularly repeating pattern of atomic, physical, and chemical properties with increasing atomic number
  • ​The Periodic Table can be split into s-, p-, d-, and f- blocks. Which is determined by which orbital the highest energy electron is in.

Period 3

  • Across period 3, the trend in meting point relates to the structure of the elements. The melting point increases from Na to Al as the ionic charge and the number of delocalized electrons increase. Silicon has a giant covalent structure with strong covalent bonds. P4, S8, and Cl2 are all simple molecular covalent substances. From P4 to S8 there are more electrons and stronger London forces. Form S8 to Cl2 to Ar there are fewer electrons and weaker London forces.
  • Across the period, the atomic radius decreases as effective nuclear charge increases and there is no increase in shelving.
  • Across the period, the ionization energy increases as nuclear charge increases.
    • Aluminum is an exception as the 3s electrons shield the 3p electron
    • Sulfur is an exception as an electrons is being removed from an p orbital containing 2 electrons, so there is electron pair repulsion

Properties of Period 3 Elements

  • All of the Period 3 elements can react with oxygen to form oxides to form Na2O, MgO, Al­­2O3, SiO2, P4O10, SO2 and SO3
  • ​Sodium burns with a yellow flame, magnesium burns with a white flame, aluminum with a brilliant white flame and sulfur with a blue flame.

Trends in the reaction of the elements with water

2 Na (s) + 2 H2O (l) → 2 NaOH (aq) + H2 (g)

Mg (s) + H2O (g) → MgO (s) + H2 (g)

Trends in the reaction of the elements Na, Mg, Al, Si, P and S with oxygen

4 Na (s) + O2 (g)→ 2 Na2O (s)

2Mg (s) + O2 (g)→ 2MgO (s)

4Al + 3 O2 (g)→ 2Al2O3(s)

 Si + O2 (g)→ SiO2 (s)

4P + 5 O2 (g)→ P4O10 (s)

S+ O2 (g)→SO2 (g)

Acid base reaction between period 3 oxides and simple acids and bases.

The basic oxides react with acids to make salts

Na2O (s) + 2 HCl (aq) → 2NaCl (aq) + H2O (l)

Na2O (s) + H2SO4 (aq) → Na2SO4 (aq) + H2O (l)

MgO (s) + 2 HCl (aq) →MgCl2 (aq) + H2O (l)

 Na2O (s) + 2H+ (aq) → 2Na+ (aq) + H2O (l)

 MgO (s) + 2 H+ (aq) → Mg2+ (aq) + H2O (l)

  • Sodium and magnesium , electropositive metals, reacts with water to produce the metal oxide and hydrogen
  • Aluminum, a less electropositive metal, reacts initially with water to produce hydrogen but the surface coating of the oxide that is formed stops the reaction
  • Silicon, phosphorus and Sulphur, non-metals, do not react with water
  • Chorine, a halogen, reacts with water to form an acidic solution.