Formation of Ions: Cations and Anions
- Have you ever wondered how table salt ($NaCl$) dissolves in water and allows electricity to flow?
- The key lies in ions, charged particles formed when atoms gain or lose electrons.
What Are Ions?
Definition
Ion
An ion is an atom or group of atoms that has gained or lost electrons, resulting in a net electrical charge.
Ions are classified into two main types: cations and anions.
Cations: Positive Ions
Definition
Cation
A cation is formed when an atom loses one or more electrons, resulting in a net positive charge.
Metals, which are found on the left side of the periodic table, tend to lose electrons because they have relatively low ionization energies.Example
Sodium (Na) loses one electron to form a sodium ion:
$$ \text{Na} \rightarrow \text{Na}^+ + e^- $$
Anions: Negative Ions
Definition
Anion
An anion is formed when an atom gains one or more electrons, resulting in a net negative charge.
Non-metals, which are found on the right side of the periodic table, tend to gain electrons because they have high electron affinities.Example
Chlorine (Cl) gains one electron to form a chloride ion:
$$ \text{Cl} + e^- \rightarrow \text{Cl}^- $$
Remember that metals form cations by losing electrons, while non-metals form anions by gaining electrons.
Predicting the Charge of Ions
- The charge of an ion can be predicted based on the electron configuration of the atom and its position in the periodic table.
- Atoms tend to lose or gain electrons to achieve a stable noble gas configuration (full outer shell).
Main Group Elements
- Group 1 (Alkali Metals): Lose 1 electron to form $+1$ ions (e.g., $\text{Na}^+$, $\text{K}^+$).
- Group 2 (Alkaline Earth Metals): Lose 2 electrons to form $+2$ ions (e.g., $\text{Mg}^{2+}$, $\text{Ca}^{2+}$).
