Sodium (Na):
* Reactivity: Sodium is a highly reactive alkali metal. It readily loses its outermost electron to form a positively charged ion (Na+).
* Reaction with Water: When sodium comes into contact with water, a vigorous reaction occurs. The sodium atom donates its electron to a water molecule, forming a sodium ion (Na+) and a hydroxide ion (OH-). This reaction releases a significant amount of energy, often causing the sodium to melt and even ignite.
* Formation of Sodium Hydroxide: The sodium ions and hydroxide ions react further to form sodium hydroxide (NaOH), which is soluble in water. This dissolves the sodium completely.
Copper (Cu):
* Lower Reactivity: Copper is a transition metal and is less reactive than sodium. It holds onto its electrons more tightly.
* No Significant Reaction: While copper can react with certain acids (like nitric acid), it doesn't react readily with water. The reaction with water is not energetically favorable enough to overcome the strong metallic bonding in copper.
* Oxidation: Copper does oxidize (react with oxygen) in the presence of air and moisture, forming a green patina (copper oxide). This patina acts as a protective layer, preventing further oxidation.
In summary: Sodium dissolves in water because of its high reactivity and its tendency to form ions that readily dissolve in water. Copper, being less reactive, doesn't undergo a significant reaction with water, and its oxidation in air forms a protective layer that prevents further reaction.
