Question

Explain why aluminium in the periodic table has a higher melting point than sodium?

Answer 1

Increasing strength of metallic bonds.

Explanation:

In Period 3 of the Periodic Table, the 3s and 3p orbitals are filled with electrons. Atomic number increases across period 3.

Electron configurations of Period 3 elements:

Na [Ne] 3s1
Mg [Ne] 3s2
Al [Ne] 3s2 3px1
Si [Ne] 3s2 3px1 3py1
P [Ne] 3s2 3px1 3py1 3pz1
S [Ne] 3s2 3px2 3py1 3pz1
Cl [Ne] 3s2 3px2 3py2 3pz1
Ar [Ne] 3s2 3px2 3py2 3pz2

Reasons for varying melting points across period 3( from left to right):

• Higher atomic number (proton number)- Al has more protons than Na, nuclei of Al is more positively charged

• Atomic radius decreases-the delocalised electrons are closer to the positive nuclei, stronger electrostatic attractions between positive nuclei and delocalised electrons

• Number of electrons of each atom increases- Number of protons= Number of electrons, therefore Al also has more delocalised electrons than Na

• Higher number of both positive protons and delocalised electrons in Al-stronger electrostatic attractive forces within the atoms

The stronger the attractive forces within atoms, the more difficult it is to break those intramolecular forces (metallic bonds in this case), therefore the melting point is higher.