1
Q
What is the trend in atomic radius across Period 3?
A
- Decrease in radius from Na to
- Nuclear charge increases, shielding stays relatively constant
- Greater attraction from nucleus to valence electrons
2
Q
What is the trend in ionic radius across Period 3?
A
- Decrease in radius from Na to Si (cations) due to increase in positive nuclear charge yet same electron configuration
- Jump from Si to P due increase in shielding as switch from cation to anion
- Decrease in radius from Si to Cl (anions) due to increase in nuclear charge
3
Q
What is the trend in melting point across Period 3?
A
- Na to Al increase due to increase in cation charge, greater ESFA to delocalised e-
- Al anomaly due to electron in 3s2 orbital, partial shielding causes weaker attraction
- Si has highest MP due to strong bonds in giant covalent structure, requires a lot of energy to break
- P4, S8, Cl2 all simple covalent molecules, only experience London forces, MP ∝ number of e-
- Ar has lowest MP as single atoms, only very weak London forces to overcome
4
Q
What is the trend in electrical conductivity across Period 3?
A
- Na to Al increase due to increase in number of delocalised electrons free to carry charge
- Silicon is a semiconductor
- The rest are insulators due to lack of delocalised electrons
5
Q
What is the trend in ionisation energy across Period 3?
A
- General increase due to increase in number of protons, constant shielding, stronger ESFA
- Mg to Al drop as ionising from a higher energy orbital
- P to S drop as electron pairing creates repulsion
