Chemistry – The Periodic Table - Group I properties | e-Consult

As you move down Group I (Lithium, Sodium, Potassium), there are clear trends in the physical properties of these metals.

• Melting Point: The melting point decreases as you go down the group. Lithium has the highest melting point (180°C), while potassium has the lowest (60°C). This is because the metallic bonding becomes weaker with increasing atomic size. Larger atoms have a greater distance between their valence electrons and the nucleus, resulting in weaker attraction and therefore lower melting points.
• Density: The density increases as you move down the group. Lithium is the least dense (0.53 g/cm³), and potassium is the most dense (0.89 g/cm³). This is also related to the increasing atomic size. While the number of protons and neutrons increases, the volume increases more significantly, leading to a higher density.
• Reactivity: The reactivity increases down the group. Lithium is relatively unreactive, sodium is reactive, and potassium is the most reactive. This is because the outermost electron is further from the nucleus in larger atoms, making it easier to remove and form a positive ion. The ease of losing an electron increases down the group, leading to greater reactivity with water and other substances.