5.1.1 The Atom
In this section we explore how atoms can become ions by gaining or losing electrons. Think of atoms as tiny batteries that can either give away or take in electrons to balance their charge. ⚛️
Positive Ions (Cations)
When an atom loses one or more electrons, it becomes a positive ion (cation). The loss of negatively charged electrons leaves a net positive charge.
- Example: Sodium (Na) loses one electron to form \$Na^+\$.
- Analogy: Imagine a person (atom) who gives away a friend (electron) – the person feels lighter (positive).
Negative Ions (Anions)
When an atom gains electrons, it becomes a negative ion (anion). The extra electrons give a net negative charge.
- Example: Chlorine (Cl) gains one electron to form \$Cl^-\$.
- Analogy: Think of a person who invites a new friend (electron) – the person feels heavier (negative).
How to Predict Ion Formation
- Look at the element’s position in the Periodic Table.
- Elements in Group 1 (alkali metals) usually lose one electron.
- Elements in Group 17 (halogens) usually gain one electron.
- Transition metals can lose or gain multiple electrons.
Illustrative Table of Common Ions
| Element | Common Ion | Charge |
|---|
| Na | Sodium ion | \$Na^+\$ |
| Cl | Chloride ion | \$Cl^-\$ |
| Ca | Calcium ion | \$Ca^{2+}\$ |
| O | Oxide ion | \$O^{2-}\$ |
Exam Tips
🔍 Key points to remember:
- Identify the element’s group to predict electron loss/gain.
- Remember that losing electrons gives a positive charge (\$+n\$), gaining gives a negative charge (\$-n\$).
- For ions with a charge of 2, the element usually has to lose or gain two electrons (e.g., \$Mg^{2+}\$ or \$O^{2-}\$).
- Use the formula \$Z - N\$ to check if the atom is neutral (where \$Z\$ = atomic number, \$N\$ = number of neutrons).
💡 Practice: Write the ion formed by potassium (K) and fluorine (F) and check the charge.