Question

propose explanations for the trends you have described for ionic radii within groups and across periods

Answer 1

There are several explanations for the trends in ionic radii within groups and across periods in the periodic table:

• Within groups: Ionic radii generally increase as you move down a group. This is because the atomic radii of the elements in a group generally increase as you move down the group. This is due to the increasing number of energy levels and valence electrons as you move down the group. As the atomic size increases, the ionic size also increases.

• Across periods: Ionic radii generally decrease as you move from left to right across a period. This is because the atomic size generally decreases as you move from left to right across a period due to the increasing effective nuclear charge (the number of protons in the nucleus) and the decreasing number of energy levels. As the atomic size decreases, the ionic size also decreases.

• Charge: The ionic charge also plays a role in determining the ionic radius. For a given element, the ionic radius will generally be larger for a lower charge and smaller for a higher charge. This is because a higher charge leads to a stronger attractive force between the positive nucleus and the negative electrons, leading to a smaller size.

• Structure: The type of crystal structure can also affect the ionic radius. For example, cations in a cubic crystal structure generally have a smaller ionic radius than those in a hexagonal crystal structure.

Overall, these trends in ionic radii can be explained by the interplay between the atomic size, effective nuclear charge, and the number of valence electrons of the elements.

Answer 2

Ionic radii are a measure of the size of ions, which are atoms or molecules that have gained or lost electrons and therefore have a net electric charge. The ionic radii of elements within a group or a period can show certain trends due to the properties of the elements and the way in which their electron configurations change.

Within a group:

Within a group, ionic radii tend to increase as you go down the group. This is because elements in the same group have the same number of valence electrons (the electrons in the outermost energy level of an atom), but as you go down the group, the number of energy levels (shells) increases. This means that the outermost electrons are farther away from the nucleus, which leads to a larger atomic radius. When an atom loses or gains an electron to become an ion, the ionic radius will be similar to the atomic radius, so the ionic radii of elements within a group will also increase as you go down the group.

Across a period:

Across a period, ionic radii tend to decrease as you go from left to right. This is because elements in the same period have the same number of shells, but as you go from left to right, the number of protons (and therefore the atomic number) increases. This increases the positive charge of the nucleus, which attracts the electrons more strongly. As a result, the electrons are held closer to the nucleus, leading to a smaller atomic radius. When an atom loses or gains an electron to become an ion, the ionic radius will be similar to the atomic radius, so the ionic radii of elements across a period will also decrease as you go from left to right.

It is important to note that these trends are not always absolute and there can be some exceptions due to other factors such as electron shielding and the electron configurations of the elements.