Half the distance between nuclei of bonded identical atoms; it decreases across a period and increases down a group.
Practise Atomic Structure & Periodicity All Atomic Structure & Periodicity topics
Atomic radius is the size of an atom, usually taken as half the distance between the nuclei of two bonded identical atoms. It decreases across a period because Z_eff rises while the electrons stay in the same shell and are pulled closer. It increases down a group because each step adds a new shell of electrons. Radii can be measured as covalent, metallic or van der Waals values, which differ in definition and magnitude. Noble gases are quoted only as van der Waals radii.
Key ideas: Atomic radius is half the distance between two bonded nuclei (covalent) or nonbonded (van der Waals), typically 30 to 300 pm. It decreases across a period (Z_eff rises) and increases down a group (more shells). Examples: Na 186 pm, Cl 99 pm, Cs 265 pm. Covalent radii are additive: bond length is approximately r_A + r_B.
Common mistakes and connections: Students compare different types of radii, such as a covalent radius of one atom with the van der Waals radius of another. Noble gases show large values because van der Waals radius is used. Another error is predicting increase across a period because of more electrons. It leads to ionic radius, ionization energy and metallic character.
Atomic radius shrinks across period 2 from 152 pm for lithium to 71 pm for fluorine because the nuclear charge grows with the same shell. The interactive lesson shows this as a live animation or chart.
Going from lithium to fluorine across period 2, the atoms become smaller even though each added electron joins the same shell.
Half the distance between nuclei of bonded identical atoms; it decreases across a period and increases down a group.
Atomic Radius is a beginner topic in Atomic Structure & Periodicity. It needs no earlier chemistry lessons and is a good starting point.
Study these earlier topics in Atomic Structure & Periodicity first: d-Block Elements, f-Block Elements, Metals Nonmetals and Metalloids.
The next topics in Atomic Structure & Periodicity are Ionic Radius and Isoelectronic Species.
Yes. The interactive lesson includes a self-check question on Atomic Radius, and the Atomic Structure & Periodicity quiz draws on every topic in this area.
Atomic Radius is topic 83 of 115 in Atomic Structure & Periodicity.