Is there regular decrease in atomic radii of 3d series?

Question

The following fragment of the table of atomic radii from CrystalMaker — Elements, Atomic Radii and the Periodic Table shows a regular decrease in the atomic radius of 3d series:

Table of Atomic Radii

The following table contains some of the atomic radius data used by CrystalMaker. This is a brief summary of a far more extensive body of work — please see the notes at the end of this page for more information. $$ \begin{array}{ccc} \hline \text{Atomic} & \text{Element} & \text{Atomic} \\ \text{Number} & \text{Symbol} & \text{Radius [Å]} \\ \hline \vdots & \vdots & \vdots \\ 21 & \ce{Sc} & 1.84 \\ 22 & \ce{Ti} & 1.76 \\ 23 & \ce{V} & 1.71 \\ 24 & \ce{Cr} & 1.66 \\ 25 & \ce{Mn} & 1.61 \\ 26 & \ce{Fe} & 1.56 \\ 27 & \ce{Co} & 1.52 \\ 28 & \ce{Ni} & 1.49 \\ 29 & \ce{Cu} & 1.45 \\ 30 & \ce{Zn} & 1.42 \\ \vdots & \vdots & \vdots \\ \hline \end{array} $$

Notes

1. Atomic Radii: values are calculated from:
   E Clementi, D L Raimondi, W P Reinhardt (1963) J Chem Phys. 38:2686.

While comparing atomic radii, two factors are important:

1. Decrease in size due to increase in effective nuclear charge.
2. Increase in size due to increase in shielding effect.

I was surprised to find a regular decrease in the atomic radius of 3d series elements on this site because that would mean that effective nuclear charge is dominating in case of each element more than shielding factor. On some posts like Variation in atomic sizes in the transition elements I have found that from Ni to Zn there is a regular increase in size.

Are the values shown on this site wrong? If yes, what are the correct values?

If not, why shielding wouldn't be as effective as increase in nuclear charge?

Answer 1

Periodic Table Website confirms these atomic radii. So why does the atomic radius decrease? The nucleus of the atom gains protons moving from left to right, which increases the positive charge of the nucleus which attracts electrons. Although electrons are also added as the elements move from left to right across a period, these electrons reside in the same energy shell and therefore do not offer increased shielding.

Source: Periodic Trends

Answer 2

According to Work Out Chemistry ‘A’ Level^[1], there should be some mistake in the data.

In $\mathrm{3d}$ series, radius of $\ce{Zn}$ is greater than that of $\ce{Cu}$. The thing that brings difference in atomic size is effective nuclear charge. When the increase in nuclear charge and shielding is different, atomic radius changes.

• When increase in nuclear charge is greater than increase in shielding, atomic radius decreases. This is the case form $\ce{Sc}$ to $\ce{Mn}$.

• When increase in nuclear charge is equal to increase in shielding, atomic radius remains almost constant. This is the case for $\ce{Fe}$, $\ce{Co}$ and $\ce{Ni}$.

• When increase in nuclear charge is less than increase in shielding, atomic radius increases. This is the case for $\ce{Cu}$ and $\ce{Zn}$.

Figure 23.1 The Metallic Radii of the First-, Second-, and Third-Row Transition Metals

Reference:

[1]: Burgess, D. A. The D-Block Elements. In Work Out Chemistry ‘A’ Level; Macmillan Education UK: London, 1987; pp 150–157.