Periodic Properties - Atomic Radius Or Atomic Size

Atomic size refers to the distance between the nucleus of an atom and its outermost shell. It is commonly expressed as atomic radius, measured in picometres (pm).

Atomic Radius: Defined as half the distance between two adjacent atoms of the same element in a molecule.

Types of Atomic Radii:

• Covalent Radius: Measured in nonmetals by forming a single covalent bond.
• Metallic Radius: Measured in metals as half the distance between two metal nuclei.

Measurement Techniques: Determined using X-ray diffraction or spectroscopy methods.

Across a Period (Left to Right):

• Atomic radius decreases due to increasing nuclear charge.
• Electrons are added to the same outermost shell, increasing electrostatic attraction and pulling electrons closer to the nucleus.

Example:

Down a Group (Top to Bottom):

• Atomic radius increases because a new electron shell is added, increasing the distance between the nucleus and the outermost electron.
• Even though nuclear charge increases, the effect of electron shielding causes atoms to become larger.

Example:

• Higher nuclear charge → Stronger attraction → Smaller atomic size.
• More electron shells → Increased shielding → Larger atomic size.