What Is Atomic Radius?
Atomic radius is a measure of the size of an atom. Since an atom's electron cloud does not have a definite boundary, the atomic radius is typically defined as half the distance between the nuclei of two identical atoms that are bonded together. It provides a way to estimate the volume occupied by an atom.
Section 2: Key Periodic Trends
The size of the atomic radius follows predictable patterns on the periodic table. It generally decreases as you move from left to right across a period because the increasing number of protons pulls the electron shells closer to the nucleus. Conversely, the atomic radius increases as you move down a group because new electron shells are added, placing the outermost electrons further from the nucleus.
Section 3: A Practical Example
Consider sodium (Na) and chlorine (Cl), which are in the same period. Sodium has a larger atomic radius than chlorine because chlorine has more protons, creating a stronger pull on its electrons. Now compare sodium (Na) and potassium (K), which are in the same group. Potassium has a larger atomic radius because it has an additional electron shell compared to sodium.
Section 4: Importance of Atomic Radius
Understanding atomic radius is crucial because it directly influences an atom's chemical properties. It affects other key trends like ionization energy, electron affinity, and electronegativity. For instance, smaller atoms tend to hold onto their valence electrons more tightly, requiring more energy to remove them and influencing the types of chemical bonds they can form.