Thinking about the periodicity of the period 3 elements, explain the structure of the Sodium and Phosphorus Oxides and the acid-base behaviour of the Oxide solutions.

Electronegativity increases across a period because the atomic radius decreases (i.e. the valence electrons are closer to the nucleus and experience a higher attraction). This is because there are more protons in the nucleus (higher positive charge) whilst screening by inner electrons remains relatively constant. Na2O has an ionic lattice structure because there is a big electronegativity difference between Na and O so O attracts the shared electrons more strongly. P4O10 has a covalent molecular structure because there is a much smaller electronegativity difference between P and O so neither attracts the shared more strongly.In solution Na2O --> 2Na+ + O2-. O2- is a strong oxidising agent and reacts with H2O to form OH-, a strong base. In full, Na2O +H2O --> 2NaOH. P4O10 + 6H2O --> 4H3PO4, this is a weak acid but some H+ is liberated.