Classify the following compounds as electrolytes or non-electrolytes. (a) potassium chloride, KCl. (b) hydrogen peroxide, \(\mathrm{H}_{2} \mathrm{O}_{2}\). (c) methane, \(\mathrm{CH}_{4}\) (d) barium nitrate, \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\).

When exploring the nature of chemical substances, understanding the difference between ionic and covalent compounds is fundamental.

Ionic compounds are formed through the electrical attraction between positively charged ions (cations) and negatively charged ions (anions). A classic example is table salt, sodium chloride (NaCl). These compounds typically have high melting and boiling points, are soluble in water, and when dissolved or melted, they conduct electricity. This is due to the movement of ions, which are the carriers of electric charge.

In contrast, covalent compounds involve the sharing of electron pairs between atoms. These shared electrons glue the atoms together into a molecule. Covalent bonds can be found in a variety of substances, ranging from gases like oxygen (O2) and nitrogen (N2), to liquids like water (H2O), and even to some solids like sugar (C12H22O11). Covalent compounds do not conduct electricity in their solid or liquid state because they do not have free-moving charges. When dissolved in water, they may remain as intact molecules if they are nonpolar, or if polar, they may not dissociate into ions, a prerequisite for electrical conductivity.

The concept of electrical conductivity in solutions refers to a solution's ability to allow the flow of electric current. This phenomenon is primarily associated with the presence of ions—charged particles—in the solution.

Electrolytes, such as salts, acids, and bases, when dissolved in solvents like water, disassociate into cations and anions. These ions are able to move freely in the aqueous solution, creating a pathway for electric current to travel. This property makes such solutions good conductors of electricity. Potassium chloride (KCl) and barium nitrate [Ba(NO3)2], for example, fall into this category when they are dissolved in water.

Non-electrolytes, however, either do not dissolve in water or do not produce ions when they do. Substances like sugar, a covalent compound, dissolve well in water but do not break into ions; therefore, a sugar solution does not conduct electricity. Similarly, certain polar molecular compounds, such as hydrogen peroxide (H2O2), can dissolve in water but remain as non-ionized molecules, resulting in a non-conductive solution.

Another important concept in chemistry is molecular polarity, which is determined by the distribution of electric charges across a molecule.

A molecule is considered polar if there is a significant difference in electronegativity between the bonded atoms, which creates a dipole moment. This difference causes a partial positive charge on one end of the molecule and a partial negative charge on the other. Water (H2O) is a classic example of a polar molecule, with the oxygen atom pulling more on the shared electrons than the hydrogen atoms.

In contrast, a molecule is nonpolar if the electrons are shared evenly by the atoms, or if polar bonds are symmetrically arranged, canceling out the dipole moments. Methane (CH4) is an example; the carbon atom is in the center with hydrogen atoms at the corners of a tetrahedron, and the electron sharing is equal, resulting in a nonpolar molecule.

Polarity impacts a molecule's physical properties, interactions with other molecules, and whether it will be miscible (able to mix) with polar or nonpolar substances. Additionally, as seen with hydrogen peroxide, even though it's polar, it does not form ions in solution, demonstrating that molecular polarity alone does not ensure electrolytic behavior.