Yes, the atomic size of silver (Ag) is remarkably similar, almost equal, to that of gold (Au). This similarity is an interesting exception to the general trend observed in the periodic table, where atomic size typically increases as you move down a group.
Understanding Atomic Size Trends
Generally, within a group of the periodic table, atomic size increases with increasing atomic number. This is because each subsequent element down a group adds a new electron shell, placing valence electrons further from the nucleus, despite an increase in nuclear charge.
However, the case of silver and gold, both in Group 11, presents a unique scenario.
The Reason for Similar Atomic Sizes
The primary reason for the unexpected similarity in the atomic sizes of silver and gold lies in a phenomenon known as the lanthanide contraction.
- Lanthanide Contraction: Gold (Au) is located in the 6th period, and its atomic number (79) means it follows the lanthanide series (elements 58-71). The 4f electrons, which begin to fill in the lanthanide series, are very poor at shielding the outer electrons from the nuclear charge. This ineffective shielding leads to a significantly stronger effective nuclear charge experienced by the valence electrons of elements that follow the lanthanides, including gold. This stronger pull from the nucleus causes the atomic radii of these elements to be much smaller than would otherwise be expected, pulling them closer in size to the elements in the preceding period.
Beyond this fundamental quantum mechanical effect, other factors also contribute to their comparable atomic sizes:
- Similar Crystal Structure: Both silver and gold typically crystallize in a face-centered cubic (FCC) lattice. This means their atoms pack in a very similar arrangement, which influences their metallic radii in a solid state.
- Almost Identical Electropositive Character: Silver and gold exhibit very similar electropositive characters, which indicates their comparable tendencies to lose electrons and form positive ions. This similarity in electronic behavior contributes to their similar metallic bonding characteristics and, consequently, their atomic sizes within the metallic lattice.
Comparative Data
To illustrate the proximity in their atomic sizes, consider the typical metallic radii:
| Element | Atomic Number | Period | Group | Metallic Radius (pm) |
|---|---|---|---|---|
| Silver | 47 | 5 | 11 | ~144 |
| Gold | 79 | 6 | 11 | ~144 |
As the table shows, their metallic radii are virtually identical, reinforcing the assertion that their atomic sizes are almost equal. This phenomenon has significant implications for their chemical and physical properties, leading to many similarities between the two noble metals.
