2.1 Periodicity

periodicity

the study of trends across the period table

atomic radius across a period

decreases as nuclear charge increases for the same no. electrons to outer electrons pulled closer due to greater attraction

atomic radius down a group

increases as an electron shell is added, increasing the distance from outer electron to nucleus, so decreasing power of attraction. also, there is increased electron shielding.

ionisation energy across a period

increases due to decreasing atomic radius and increasing nuclear charge, meaning outer electron is held stronger to more energy is required to remove it

ionisation energy down a group

decreases as nuclear attraction between outer electron and nucleus reduces and shielding increasing, so less energy is needed

melting point trend across period 3

• increases Na to Al as more positive ions so more delocalised electrons so higher electrostatic forces

• Si has the highest as its macro molecular with lots of strong covalent bonds

• P, S, Cl simple covalent with weak VdW

  • S₈ > P₄ > Cl₂ > Ar

boiling point trend across period 3

• increases Na to Al as metallic bonding gets stronger

  • Al higher that Si as covalent bonds in Si already broken

atomic radius trend across period 3

decreases as nuclear charge increases but electrons are in the same energy level so attracted more strongly

trend in 1st ionisation energy across period 3

• general increase Na to Ar as nuclear charge increases but the shielding is constant

• decreases Mg to Al as Al’s outer electron is in the more shielded 3p orbital

• decreases P to S as S has an electron pair that has natural repulsion