Sodium chloride (\(\text{NaCl}\)), commonly known as table salt, is electrically neutral as a whole, meaning it carries no net positive or negative charge. This neutrality is a fundamental rule of stable chemical compounds. However, \(\text{NaCl}\) is entirely composed of highly charged particles, and its identity is defined by the powerful attraction between these opposite electrical components, which only reveals its separated charges when dissolved in a liquid.
The Charges of Sodium and Chloride Ions
The electrically neutral nature of the solid compound is built upon two distinct, charged particles called ions. These ions are created when neutral sodium and chlorine atoms interact, driven by a tendency to achieve a stable electron configuration. Sodium (\(\text{Na}\)) starts with one electron in its outermost shell, which it readily gives up. By losing this single negatively charged electron, the sodium atom is left with one more proton than electrons, resulting in a net charge of \(+1\). This positively charged particle is termed a cation and is written as \(\text{Na}^+\).
The electron released by the sodium atom is immediately accepted by a chlorine (\(\text{Cl}\)) atom. Chlorine naturally has seven electrons in its outermost shell and requires only one more to complete a stable shell. By gaining this extra electron, the chlorine atom possesses one more negative charge than positive charges, giving it a net charge of \(-1\). This negatively charged particle is known as an anion, designated as \(\text{Cl}^-\). The formation of these oppositely charged ions defines the nature of sodium chloride.
The Overall Neutrality of Sodium Chloride
The solid compound is definitively neutral. The strong electrostatic attraction between the positive \(\text{Na}^+\) cation and the negative \(\text{Cl}^-\) anion forms an ionic bond. When these ions combine, the \(+1\) charge from the sodium perfectly cancels out the \(-1\) charge from the chloride, resulting in a net charge of zero. This precise charge balance explains why the compound itself does not carry a charge.
In its solid form, sodium chloride exists as a vast, ordered network called a crystal lattice, not as individual \(\text{NaCl}\) molecules. This structure is a rigid, repeating, three-dimensional arrangement where every \(\text{Na}^+\) ion is surrounded by six \(\text{Cl}^-\) ions, and every \(\text{Cl}^-\) ion is surrounded by six \(\text{Na}^+\) ions. Within this structure, the total count of positive charges is always equal to the total count of negative charges. Therefore, any sample of solid salt exhibits complete electrical neutrality.
How \(\text{NaCl}\) Becomes an Electrolyte in Water
The charged nature of the constituent ions becomes apparent when sodium chloride is dissolved in water. \(\text{NaCl}\) is classified as a strong electrolyte because it completely separates into its ions when placed in an aqueous solution. Water molecules are polar, meaning they have a slight negative charge near the oxygen atom and a slight positive charge near the hydrogen atoms.
When salt is added to water, the negative ends of the water molecules surround and pull apart the positive \(\text{Na}^+\) ions. Simultaneously, the positive ends of the water molecules pull away the negative \(\text{Cl}^-\) ions. This process, known as dissociation, releases the ions into the solution, allowing them to move freely. Since the solution now contains mobile charged particles, it gains the ability to conduct an electric current, which is the defining characteristic of an electrolyte solution. If an external current is applied, the positive \(\text{Na}^+\) ions migrate toward the negative electrode, and the negative \(\text{Cl}^-\) ions move toward the positive electrode.