2.1.4 Trends in Period 3 Elements : Melting Point Flashcards
1
Q
How does melting point change from Na to Al?
A
- Na to Al increases because they are metallically bonded
- With increasing delocalised electrons within the structure
- So greater electrostatic forces of attraction between protons and electrons and so more energy required to overcome them, so a higher melting point
2
Q
How does melting point change from Si to Ar?
A
- Si has highest melting point because it forms covalent bonds, and is a giant covalent structure (4 covalent bonds to neighboring Si atoms)
- Lots of energy required to overcome these strong covalent bonds hence high melting point
- P to Ar
- Simple covalent molecules (P4, S8, Cl2 and Ar)
- Covalent bonds are strong but the forces of attraction between the molecules are weak dipole induced dipole forces
- Hence not much energy required to overcome them, so MP decreases
(S has higher melting point than P because S exists as S8 and P exists as P4 so more van der waals forces)
3
Q
Electrical Conductivity across period 3
A
- Na to Al increases
- More valence electrons donated as delocalised electrons
- So Al has more electrons available to move around and carry a charge
- So Al is a better conductor than Na
- Giant covalent structure of Si has no delocalised electrons so no electrons can freely move around and carry a charge so it is a bad conductor
- The rest do not have delocalised electrons so cannot carry charge so are bad conductors of electricity