Ions and Ionic Bonds

Atoms become ions when they lose or gain electrons. Losing electrons makes a positive ion (cation). Gaining electrons makes a negative ion (anion). Atoms change electrons, not protons.

Forming Ions

• Metals (e.g. Group I) lose electrons to form cations, aiming for a full outer shell.
• Non-metals (e.g. Group VII) gain electrons to form anions, also reaching a full outer shell.

Example with sodium and chlorine:

$$\text{Na} \rightarrow \text{Na}^+ + e^-$$ $$\text{Cl} + e^- \rightarrow \text{Cl}^-$$

Now $\text{Na}^+$ and $\text{Cl}^-$ attract.

What is an Ionic Bond?

An ionic bond is a strong electrostatic attraction between oppositely charged ions. It usually forms between a metal cation and a non-metal anion (for example, sodium and chlorine).

Dot-and-cross diagrams show electrons. The transferred electron is drawn as a different symbol (a “cross”) now on the non-metal’s outer shell.

Giant Ionic Lattice

Ionic compounds form a giant lattice: a regular 3D arrangement of alternating positive and negative ions. Imagine a 3D checkerboard where each opposite piece attracts in all directions.

Properties and Explanations

• High melting/boiling points: strong attractions throughout the lattice need much energy to break.
• Electrical conductivity: poor when solid (ions fixed); good when molten or in aqueous solution (ions are free to move and carry charge).

Getting Formulas from Ion Charges

• Balance charges so the overall compound is neutral.
• $\text{Mg}^{2+}$ with $\text{O}^{2-}$ gives MgO; $\text{Ca}^{2+}$ with $\text{Cl}^-$ gives CaCl$_2$.