Atomic Radius
Definition and meaning of Atomic Radius in chemistry.
Atomic radius is the distance from the nucleus of an atom to its outermost electrons. It is typically measured in picometers (pm) and represents half the distance between the nuclei of two bonded atoms in a covalent bond.
In more detail
Atomic radius is a fundamental property that reveals how large an atom is and how its electrons are distributed. The size of an atom varies predictably across the periodic table: atoms increase in size down a group due to additional electron shells at greater distances from the nucleus, and decrease across a period from left to right due to increased nuclear charge pulling electrons closer. Understanding atomic radius is crucial for predicting chemical behavior, electronegativity, and ionization energy. Smaller, more compact atoms tend to be more electronegative and exhibit different reactivity patterns than larger atoms.
Key facts
| Measurement Unit | Picometers (pm); 1 pm = 10^-12 meters |
|---|---|
| Periodic Trend - Groups | Increases moving down (additional electron shells) |
| Periodic Trend - Periods | Decreases moving left to right (stronger nuclear attraction) |
| Field | General Chemistry |
Sodium (Na) has an atomic radius of approximately 166 pm, while the smaller chlorine (Cl) atom has a radius of about 102 pm, demonstrating the decreasing trend across the periodic table.
Frequently asked questions
How is atomic radius determined?
Atomic radius is calculated from X-ray crystallography data by measuring the internuclear distance between bonded atoms and dividing by two.
Why do atoms get smaller across a period?
Although electrons are added across a period, the nuclear charge increases faster, pulling the electron cloud closer to the nucleus and making the atom more compact.