Atomic radius what is it

Moving down a group, the number of energy shells also increases with the increase of protons and electrons. Thus the atomic radius also increases down the group in periodic table. As in the transition metals the electrons are added in the inner shell, the nucleus attracts the increasing electrons towards it more and thus the radius decreased. Definition of atomic radius The atomic radius is the size of the atom, typically measured by the distance from the nucleus of the atom to the electron clouds around the nucleus.

Ways to measure the atomic radius According to the Heisenberg uncertainty principle, it is not possible to measure the momentum and the position of the electron simultaneously. Covalent radius Covalent radius is the radius calculated when an atom is bonded covalently with another atom of same element. Metallic radius The metallic radius is the radius calculated between two metal atoms bonded together in metal cluster.

Ionic radius Ionic radius is the radius calculated when an atom is bonded with another atom in a molecule by transferring electrons to make ionic bond. Here the radius of two ions are not equal and few other things need to be discussed before we calculate the ionic radius: The atoms of different element, they must differ in electrons and protons, sometimes number of orbitals and so on.

Again the atomic radius is different because of their ionic status of the atom. The atom can be cation or anion by losing or gaining electron.

When an atom loses electron sometime it has less orbital than before. However the nucleus attract the rest of the electrons more tightly towards the nucleus. The ionic radius is thus reduced than atomic radius. In the same way the anions can have lesser radius that the radius of its original neutral atom. When a covalent bond is present between two atoms, the covalent radius can be determined. When two atoms of the same element are covalently bonded, the radius of each atom will be half the distance between the two nuclei because they equally attract the electrons.

The distance between two nuclei will give the diameter of an atom, but you want the radius which is half the diameter. Covalent radii will increase in the same pattern as atomic radii.

The reason for this trend is that the bigger the radii, the further the distance between the two nuclei. The covalent radius depicted below in Figure 1 will be the same for both atoms because they are of the same element as shown by X.

The ionic radius is the radius of an atom forming ionic bond or an ion. The radius of each atom in an ionic bond will be different than that in a covalent bond. This is an important concept. The reason for the variability in radius is due to the fact that the atoms in an ionic bond are of greatly different size.

One of the atoms is a cation, which is smaller in size, and the other atom is an anion which is a lot larger in size. So in order to account for this difference, one most get the total distance between the two nuclei and divide the distance according to atomic size. The bigger the atomic size, the larger radius it will have. If we were able to determine the atomic radius of an atom from experimentation, say Se, which had an atomic radius of pm, then we could determine the atomic radius of any other atom bonded to Se by subtracting the size of the atomic radius of Se from the total distance between the two nuclei.

So, if we had the compound CaSe, which had a total distance of pm between the nucleus of the Ca atom and Se atom, then the atomic radius of the Ca atom will be pm total distance - pm distance of Se , or pm. This process can be applied to other examples of ionic radius.

Cations have smaller ionic radii than their neutral atoms. In contrast, anions have bigger ionic radii than their corresponding neutral atoms. Figure 3 below depicts this process. An anion , on the other hand, will be bigger in size than that of the atom it was made from because of a gain of an electron.

We can get more squirrels into that same space than we can people for the same reason. Knowing the sizes of objects we are dealing with can be important in deciding how much space is needed.

The size of atoms is important when trying to explain the behavior of atoms or compounds. One of the ways we can express the size of atoms is with the atomic radius. This data helps us understand why some molecules fit together and why other molecules have parts that get too crowded under certain conditions. The size of an atom is defined by the edge of its orbital. However, orbital boundaries are fuzzy and in fact are variable under different conditions.

In order to standardize the measurement of atomic radii, the distance between the nuclei of two identical atoms bonded together is measured. The atomic radius is defined as one-half the distance between the nuclei of identical atoms that are bonded together. Figure 1. The atomic radius r of an atom can be defined as one half the distance d between two nuclei in a diatomic molecule.

Atomic radii have been measured for elements. As an example, the internuclear distance between the two hydrogen atoms in an H 2 molecule is measured to be 74 pm. Figure 2. Atomic radii of the representative elements measured in picometers. The atomic radius of atoms generally decreases from left to right across a period.