Fix the mistake: Chemical Changes and Ions

Ions and Electrolytes

Some substances conduct electricity when dissolved in water, while others do not. This difference is determined by whether ions are produced.

Basic Knowledge

An atom consists of a nucleus (protons and neutrons) at its center and electrons moving around it. Normally, the number of protons and electrons is equal, so the atom is electrically neutral. However, when it loses or gains electrons, it becomes an electrically charged particle called an ion. When an atom loses electrons, it becomes a cation (+); when it gains electrons, it becomes an anion (−).
The process in which a substance dissolves in water and separates into ions is called ionization. A substance that ionizes is called an electrolyte, while one that does not ionize is called a nonelectrolyte. Sodium chloride, hydrogen chloride, and sodium hydroxide are representative electrolytes; sugar and ethanol are representative nonelectrolytes.

Important Terms
Ion (an electrically charged atom or group of atoms)
Cation (becomes positively charged by losing electrons. Na+, Ca2+)
Anion (becomes negatively charged by gaining electrons. Cl-, OH-)
Ionization (the process in which an electrolyte dissolves in water and separates into ions)
Electrolyte (a substance that ionizes in water and conducts electricity. NaCl, HCl)
Nonelectrolyte (does not produce ions even when dissolved in water. Sugar and ethanol)

Further Study

The ionization of sodium chloride is represented as NaCl → Na+ + Cl-. The ionization of hydrogen chloride is HCl → H+ + Cl-. Electricity flows because freely moving ions are present in the aqueous solution.
In contrast, sugar (sucrose) remains in molecular form when dissolved in water and does not become ions. Therefore, sugar water conducts very little electricity. An ionic formula shows the charge in the upper right of the element symbol (examples: Mg2+, S2-). Important polyatomic ions include OH- (hydroxide ion) and SO42- (sulfate ion).

Key Points
  • Ion = an electrically charged particle. Cation(+)・anion(−)
  • Loses electrons → cation; gains electrons → anion
  • Ionization = dissolving in water and separating into ions
  • Electrolyte → aqueous solution conducts electricity
  • Nonelectrolyte → aqueous solution does not conduct electricity (sugar・ethanol)
  • Representative polyatomic ions: OH-, SO42-, NO3-, NH4+

Points to Note

① Distinguish between an electrolyte and a nonelectrolyte by determining whether it separates into ions. ② Ionization (separating into ions) and dissolution (dissolving in water) are different phenomena. Sugar dissolves but does not ionize. ③ The number showing the charge in an ionic formula is called the “valency” and is equal to the number of electrons exchanged.

Practice

  1. Write the ionization equation for sodium chloride when it dissolves in water.
  2. Explain the difference between electrolytes and nonelectrolytes, giving one example of each.
  3. When an atom becomes a cation, does it lose or gain electrons?

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