Why is ionic radius smaller

You know the rubidium cation is smaller than the rubidium atom because it had to lose an electron to form the ion. At the same time, you know rubidium lost an electron shell when it lost an electron. You know the fluorine anion is larger than the fluorine atom because it gained an electron to form the ion.

Next, look at the periodic table to determine the relative size of the atoms of the elements. A neutral tellurium is smaller than a neutral rubidium atom because atomic radius decreases as you move across a period. But, the tellurium atom is larger than the rubidium cation because it has an additional electron shell. Covalent radius, van der Waals radius, metallic radius, and Bohr radius are more appropriate in some situations. This is because the size of an atom is affected by its chemical bonding behavior.

Similarly, when an electron is added to an atom, forming an anion, the added electron repels other electrons, resulting in an increase in the size of the atom. The ionic radius is not a fixed property of a given ion; rather, it varies with coordination number, spin state, and other parameters.

For our purposes, we are considering the ions to be as close to their ground state as possible. Nevertheless, ionic radius values are sufficiently transferable to allow periodic trends to be recognized.

As with other types of atomic radii, ionic radii increase upon descending a group and decrease going across a period. Note that this only applies if the elements are the same type of ion, either cations or anions.

This article is part of the ChemHelp Tutoring Wiki. Categories : Chemistry ChemHelp. Navigation menu Personal tools Log in. The concept of the ionic radius is further complicated by the shape of atoms and ions. While particles of matter are often depicted as spheres, they aren't always round. Researchers have discovered chalcogen ions are actually ellipsoid in shape. Whichever method you use to describe atomic size , it displays a trend or periodicity in the periodic table.

Periodicity refers to the recurring trends that are seen in the element properties. These trends became apparent to Demitri Mendeleev when he arranged the elements in order of increasing mass. Based on the properties that were displayed by the known elements , Mendeleev was able to predict where there were holes in his table, or elements yet to be discovered.

The modern periodic table is very similar to Mendeleev's table but today, elements are ordered by increasing atomic number , which reflects the number of protons in an atom.

There aren't any undiscovered elements, although new elements can be created that have even higher numbers of protons. Atomic and ionic radius increase as you move down a column group of the periodic table because an electron shell is added to the atoms. Atomic size decreases as you move across a row—or period—of the table because the increased number of protons exerts a stronger pull on the electrons.

Noble gasses are the exception. Although the size of a noble gas atom does increase as you move down the column, these atoms are larger than the preceding atoms in a row.

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