Periodicity

• 1st ionisation energy increases across a period because proton number increases but shielding stays similar. Greater attraction between between the nucleus and the outermost electrons means that more energy is required to remove an electron.
• Atomic radius decreases because number of protons increases so the atoms have a greater nuclear charge and attract the electrons more strongly, pulling them closer towards the nucleus.
• Melting point Na->Al increases because charge density increases and number of delocalised electrons increases. Stronger attraction between metal ions and free electrons means more energy is needed to overcome this attraction.
• Silicon has a macro molecular structure similar to diamond. Each silicon atom is bonded to 4 others by strong covalent bonds. These must be broken in order for silicon to melt. This requires a lot of energy so m.p and b.p are high.
• P->S: •Held together by VdW forces.

  •The larger the molecule, the more electrons it contains so stronger VdW.

  •S8 has stronger VdW forces than P4 and Cl2 so more energy is required to overcome them.
• Argon exists as free gaseous atoms so is held together only by VdW forces between atoms.
• Electrical conductivity increases from Na to Al because the number of delocalised electrons per atom increases so more electrons are free to move.
• Na2O acts as a strong base, reacting with acids in a neutralisation reaction.

  Na2O + 2HCl -> 2NaCl + H2O
• MgO is another basic oxide.

  MgO + 2HCl -> MgCl2 + H2O
• Al2O3 is amphoteric, so has reactions with acids and bases.

  Al2O3 + 6HCl -> 2AlCl3 + 3H2O

  Al2O3 + 2NaOH -> 3H2O + 2NaAl(OH)4
• SiO2 acts as an acid to form a colourless solution of sodium silicate

  SiO2 + 2NaOH -> Na2SiO3 + H2O
• P4O10 acts as an acid.

  P4O10 + 6H2O -> 4H3PO4

  4H3PO4 + 12NaOH -> 4Na3PO4 + 12H2O
• SO2 acts as an acid.

  SO2 + NaOH -> NaHSO3

  NaHSO3 + NaOH -> Na2SO3 + H2O
• Mg and P burn with a white flame in oxygen.
• Na burns with an orange flame in oxygen.
• S burns with a pale blue flame in oxygen.
• Na2O and MgO are white solids.
• SiO2 is a black solid.
• What is the trend of melting point across a period in the periodic table?

  - Melting point generally increases from left to right across a period. - This is due to: - Decreasing atomic size - Increasing nuclear charge - Increasing valence electrons - Decreasing metallic character and increasing non-metallic character
• Why is melting point considered a physical property?

  Because it does not involve any chemical changes in the substance.
• How does atomic radius affect melting point?

  A smaller atomic radius leads to stronger bonds, resulting in a higher melting point.
• What is the relationship between electronegativity and melting point?

  Higher electronegativity generally correlates with stronger bonds and higher melting points.
• What is an example of an element with a very high melting point due to strong network covalent bonds?

  Carbon (as diamond)
• What are the exceptions to the trend of melting point across a period?

  1. Noble gases: Have very low melting points due to weak van der Waals forces 2. Group 13 elements: Often have lower melting points than expected (e.g., gallium) 3. Metalloids: Can have irregular trends due to unique bonding properties
• Why do noble gases have low melting points?

  Because they have very weak van der Waals forces due to their full outer electron shells.
• Why is silicon suitable for use in solar panels?

  Because of its high melting point (1,414°C) and strong covalent bonds.