Grp II - melting points

[BlackPenguin]

hi

Do any of you know why the the first four elements melting points in this grp. seem to not follow any pattern. You would expect them to increase going down the group like they do in all other grps.

The melting points are:-

*Mg: 922K
*Ca: 1112K
*Sr: 1042K
*Ba: 998K

Thanks

[Paul Robbins]

Originally Posted by BlackPenguin

hi

Do any of you know why the the first four elements melting points in this grp. seem to not follow any pattern. You would expect them to increase going down the group like they do in all other grps.

The melting points are:-

*Mg: 922K
*Ca: 1112K
*Sr: 1042K
*Ba: 998K

Thanks

Best to include the first member of the group to see any pattern.

Be: 1551K
Mg: 922K
Ca: 1112K
Sr: 1042K
Ba: 998K

The pattern is that melting points fall as you look down the group - except for Magnesium. Why does Mg behave oddly? I've no doubt there's a good explanation and if anyone knows it I'd be happy to hear it.

[crun]

Originally Posted by Paul Robbins

Why does Mg behave oddly? I've no doubt there's a good explanation and if anyone knows it I'd be happy to hear it.

Me too.

[KathChem82]

this is the only answer i can give:

Although in general, the melting point of group II elements are decreasing, the melting point for magnesium is anomalously low. This is because beryllium and magnesium have different metallic structures from the other elements in the group:

Beryllium and Magnesium have a hexagonal closed-packed structure. The top and bottom layers contain six atoms at the corner of the hexagon and a single atom in the center of each hexagon. The middle layer contains three atoms nestled between the atoms of the top and bottom layers, hence, the name close-packed.
Calcium and Strontium have a face-centred cubic structure. The unit cell consists of eight atoms at the corners of a cube and one atom at the center of each of the faces of the cube.
Barium has a body-centred cubic structure. the unit cell consists of eight atoms at the corners of a cube and one atom at the body center of the cube.

[thor3436]

im thinking it has to do w/ the electron configuration i'm going to check the orbitals and see if anything is different . just go to www.ptable.com click on orbitals in the upper right
and point the cursor at magnesium

[thor3436]

theres not much of a difference but from beryllium has [ i hope i say this right .]
a 1s2,2s2 electron shell Mg has
1s2,2s2,2p6,3s2 electron shell im no chemist so i'm sure i'm wrong
[PLEASE TELL ME IF I'M WRONG. ]