Atomic radius trends follow some easy patterns on the periodic table. Let’s break it down simply:

1. Across a Period (Left to Right):

   • The atomic radius gets smaller.
   • This happens because the positive charge in the nucleus pulls the electrons closer.
   • For example:
     • Lithium (Li) has a radius of 152 picometers (pm).
     • Neon (Ne) has a radius of 38 picometers (pm).

2. Down a Group (Top to Bottom):

   • The atomic radius gets bigger.
   • This is because new electron shells are added, which makes the radius increase more than the pull from the nucleus.
   • For example:
     • Lithium (Li) again has a radius of 152 picometers (pm).
     • Cesium (Cs) has a much larger radius of 262 picometers (pm).

3. General Trends:

   • The elements in Group 1, known as alkali metals, have the largest atomic radii.
   • The elements in Group 18, called noble gases, have the smallest atomic radii in their groups.

These are the main ideas about atomic radii and how they change on the periodic table!