Group 1 metals are called the alkali metals. They are the first vertical line in the periodic table and include the elements lithium, sodium, potassium, rubidium, and cesium (hydrogen is not really included here). The melting points of these metals decrease as the atomic number increases, or as you go from top to bottom. This is due to the fact that the atomic radius or size increases as you go down the group as well. The larger the atomic radius is, the further away the valence electrons are located from the nucleus of the atom. And the further away the valence electrons are from the nucleus, the easier they are to disrupt and therefore to change the phase from a solid to a liquid. This means that less energy is required to melt the metal, so the melting point decreases.
Group I metals are also called the alkali metals. These group of metals is composed of Lithium (L), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs), and Francium* (Fr). Generally, the boiling point of the alkali metals goes down as you go down the group.
Metal Melting point (in Kelvin) Boiling point (in Kelvin)
Li 454 1615
Na 371 1156
K 337 1032
Rb 312 961
Cs 302 944
Fr* 900 950
*due to nuclear issues, the chemistry of Francium is not yet fully understood.