Answer
The atomic radius of hafnium breaks the general trend of increasing atomic size going down a group due to the lanthanide contraction effect.
Work Step by Step
The atomic radius generally increases going down a group in the periodic table due to the addition of new energy levels or shells. As we move down a group, each successive element has an additional energy level, resulting in an increase in atomic size.
However, in the case of hafnium (Hf), we observe that its atomic radius is unexpectedly smaller than that of zirconium (Zr), which is located above it in the same group. This deviation from the expected trend can be attributed to the phenomenon known as the lanthanide contraction.
The lanthanide contraction refers to the decrease in atomic radii that occurs as we move from the elements in the main group to the elements in the lanthanide series. This contraction is caused by the poor shielding effect of the 4f electrons in the lanthanide series, which leads to a stronger attraction between the positively charged nucleus and the outermost electrons.
In the case of hafnium, it is located immediately after the lanthanide series, specifically after the element lutetium (Lu). As a result, hafnium experiences a significant contraction in its atomic radius due to the influence of the 4f electrons. This contraction compensates for the expected increase in atomic size due to the addition of a new energy level, resulting in a smaller atomic radius compared to zirconium.
Therefore, the atomic radius of hafnium breaks the general trend of increasing atomic size going down a group due to the lanthanide contraction effect.
