Elements of Groups 16, 17 and 18 — Chemistry STD 12 Science — Question

Density :

• The density of group 16 elements increases down the group.
• On moving down the group, the increase in atomic mass is more than the increase in atomic size.
• Down the group the magnitude of van der Waals forces of attraction increases resulting in compact lattice formation of elements.

Therefore the density increases down the group. The density increases in the order $O < S < Se < Te$ Melting and boiling point :

• The melting and boiling points of the elements increase regularly on moving down the group.
• However, the melting and boiling points of polonium are lower than that of tellurium.
• This is because the intermolecular van der Waals forces are weaker in polonium.
• There is also a large difference in the melting and boiling points of oxygen and sulphur as oxygen has a smaller size, while sulphur has a larger size and stronger van der Waals forces.
  
  

  Element	O	S	Se	Te	Po
  Melting point (K)	55	393	47wQbNPTDJp9hMYdvogK2hAUiHsGeiybwaWe36bwtRQ3UTpYV7YuZ8FV5j9nauFCWwcjM6dTzpL5s2N79Rp5unwdMvc8ZKUstyle="width: 42.7227%;">Boiling point (K)	90	718	958	1260	1235