Final answer:
The atomic radius trends in the periodic table can be explained by two main factors: the group trend and the periodic trend.
Step-by-step explanation:
The atomic radius trends we see in the periodic table can be explained by two main factors:
- Group Trend: As you go down a group (or column) of the periodic table, the atomic radii increase. This is because the valence electron shell is getting larger and there is a larger principal quantum number, so the valence shell lies physically farther away from the nucleus.
- Periodic Trend: As you go across a period (or row) of the periodic table, the atomic radii generally decrease. This is because, within a period, protons are added to the nucleus as electrons are being added to the same principal energy level, leading to increased nuclear charge and a stronger force of attraction between the nucleus and electrons. This pulls the electrons closer to the nucleus, reducing the size of the atom.
Overall, the atomic radius trends in the periodic table reflect the balance between the increasing positive nuclear charge and the increasing number of occupied principal energy levels.