* Atoms change their properties when they form molecules: Sodium (Na) is a highly reactive metal, meaning it readily reacts with other substances. Chlorine (Cl) is a toxic gas. However, when they combine to form sodium chloride (NaCl), or table salt, they create a stable, non-toxic compound that we use daily.
* Atoms share or transfer electrons: The reactivity of sodium and chlorine is due to their electron configurations. Sodium has one loosely held electron in its outermost shell, while chlorine has seven. When they combine, sodium *transfers* its electron to chlorine. This creates a sodium ion (Na+) with a positive charge and a chloride ion (Cl-) with a negative charge. These opposite charges attract each other strongly, forming the ionic bond that holds the salt molecule together.
* New substances with different properties are formed: This is the fundamental principle of chemistry. When atoms combine in specific ways, they form entirely new substances with properties distinct from their constituent elements. Table salt is very different from sodium metal or chlorine gas.
In summary: When atoms form molecules, they undergo a fundamental transformation. They change their electronic configurations, resulting in a new substance with unique properties. This process involves either sharing or transferring electrons, leading to the formation of chemical bonds.
