Explaining trends in reactivity
The reactivity of Group 1 elements increases going down the group. This is because on going down the group:
- The atoms get larger. The atomic radii increase with atomic number down the group. Each succeeding element has its electron in one more shell than the previous element.
- The outer electron gets further away from the influence of the nucleus. Therefore, the attractive force between the nucleus and the electron gets weaker and so the electron is more easily given up.
| Lithium (Li) | Sodium (Na) | Potassium (K) |
|---|---|---|
 |
 |
 |
| 2.1 | 2.8.1 | 2.8.8.1 |
| Potassium is more reactive than lithium although they both need to lose only one electron to have full outer shells. This is because the outer electron of potassium atom is further from the positive attractions of the nucleus compared to the outer electron of lithium. Therefore, it is easier for potassium to lose its outer electron. | ||