Why is that the elements in the fourth group in the periodic table have high boiling point?

Answer 1

4th group elements have 4 valence electrons.So they have the ability to form 4 covalent bonds with other atoms in a tetrahedral manner .In this way they form a lattice where each atom is surrounded by 4 similar atoms.therefore a large amount of energy is needed to break all these covalent bonds .Therefore 4th group elements have high melting points and boiling points

Answer 2

Solids, whether pure elements or in general, are crystals made up of ions or molecules, or in rare cases like diamond a single compound of covalent bonds. The thermal stability of a crystal depends on the electrostatic (electrical charge, dipol or quadrupol) property of the constituents and their orientation, as well as their ability to retain constituents placed on the surface to the liquid. Electrostatic forces depend on the charge (or partial charge in case of dipols) and the inverse squared distance of the charges. Quadrupol forces aka Van der Waals forces depend on the inverse sixth potency of the charge.

Usually crystals made up of molecules break up into single molecules when melting. In the liquid these molecules still interact with each other, until at boiling point these interactions aren't strong enough to retain the molecules in the liquid. Crystals made up of ions create ionic melts held together by electrostatic attraction. This isn't found for pure elements, though. Metals are similar in the liquid and solid state, with ionized atoms surrounded by a dislocated electron cloud. Covalently bonded crystals don't melt, but may transform into different compounds.

Note that most elements have several different solid states.

Elemental carbon can be found as monomer or low-count polymer fragments in the gaseous phase, no liquid phase (except Buckminster Fullerenes) that I know of and several very different solid phases: graphite (thermodynamically most stable form), diamond, and Buckminster Fullerenes and variations thereof which don't really behave like a solid.

Several gaseous elements have no known solids at normal pressure. Iodine has no liquid phase at normal pressure.

In a very general sense, the stronger the attractive forces between the elemental constituents, the more stable the solid/liquid phase. Covalently bonded elements tend to have higher melting points than metals, which in turn tend to have higher melting points than elements occurring in distinct molecules. Quite often the solid and even liquid phases include a change of atomic structure and nature of the bonds. Even in the gaseous phase, sometimes pairing of neutrally charged molecules may occur