Atomic radius

Atomic radius refers to the size of an atom, which is typically measured in terms of the distance from the nucleus of the atom to its outermost electron shell. The atomic radius is not a fixed value, but varies depending on the atom's state and chemical environment.

Definition

The atomic radius is defined as half the distance between the nuclei of two atoms of the same element that are bonded together. This is known as the covalent radius. Another way to define the atomic radius is the van der Waals radius, which is the half the distance between the closest approach of two non-bonded atoms of the same element.

Factors affecting atomic radius

Several factors can affect the size of an atom's radius. These include:

• Atomic number: The number of protons in an atom's nucleus can affect its size. As the atomic number increases, the atomic radius generally decreases. This is because the increased number of protons creates a stronger attraction to the electrons, pulling them closer to the nucleus.

• Electron configuration: The arrangement of electrons in an atom's electron shells can also affect its size. Atoms with more filled electron shells generally have larger atomic radii.

• Ionization energy: The energy required to remove an electron from an atom can affect its size. Atoms with higher ionization energies generally have smaller atomic radii.

Trends in atomic radius

In the periodic table, there are observable trends in atomic radius. Moving from left to right across a period, the atomic radius generally decreases. This is due to the increase in the number of protons, which pulls the electrons closer to the nucleus. Moving down a group, the atomic radius generally increases. This is due to the addition of electron shells as you move down the group.

Measurement

The atomic radius is typically measured in picometers (pm) or angstroms (Å). One picometer is equal to one trillionth of a meter, and one angstrom is equal to one ten-billionth of a meter.

See also

• Ionic radius
• Covalent radius
• Van der Waals radius
• Periodic trends