8.2 - Properties of period 3 elements

Question 1

Atomic radius decreases across period 3 because: (2)

Answer 1

• As protons are added across a period, the nuclear charge increases. This results in a stronger electrostatic attraction between the nucleus and the outer electrons, drawing the outer electrons closer to the nucleus.
• The electrons added across a period go into the outer energy level, so provide little additional shielding for inner electrons.

Question 2

Melting and boiling points across period 3 (Argon)

Answer 2

lowest m.p and b.p - atoms don’t form any bonds and contains very weak induced dipole dipole forces
minimal energy required to overcome the force

Question 3

Melting and boiling points across period 3 (Phosphorous, sulfur and chlorine)

Answer 3

Phosphorous, Sulphur and Chlorine;
* simple molecular structures with weak dipole-dipole forces
* IMFs are easily overcome requiring little energy - results in low MP and BP
* sulphur has the highest melting and boiling points as it contains the most electrons between the 3, larger S8 molecules allow stronger induced dipole dipole forces to form between teh molecules
* Chlorine - lowest melting and boiling point - contains the fewest electrons - resulting in weak IMF between Cl2 molecules

Question 4

Melting and boiling points across period 3 (Silicon)

Answer 4

Silicon;
* has a giant covalent structure - each atom is covalently bonded to 4 neighbouring atoms in a tetrahedral arrangement - forms very strong bonds to link all the atoms in a 3D lattice - huge amount of energy is required to break these covalent bonds - results in high MP and BP

Question 5

Melting and boiling points across period 3 (Na, Mg and Al)

Answer 5

for Na, Mg and Al;
* B.P increase due to the strength oif the metallic bond increasing
* the metallic bond strength increases as the ions have a larger charge and the ions have a smaller ionic radius - more delocalised electrons
* results in a stronger electrostatic force of attraction between metal cations and the delocalised electrons which requires increasing amounts of energy to overcome