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
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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)

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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
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