Gold’s fake inertness: protected by bodyguards
▼ Summary
– Gold is one of the few metals that does not oxidize, unlike silver and copper from the same periodic table column.
– Gold lacks the catalytic properties of platinum and was thought to be inert until gold nanoparticles were found to act as catalysts.
– A new explanation suggests gold’s inertness comes from its crystal surfaces, not from the atom itself.
– The traditional reasoning for gold’s inertness is that its partially filled, reactive orbitals are shielded by outer, fully filled orbitals.
– The discovery of catalytic activity in gold nanoparticles revealed that the traditional explanation for gold’s inertness was incomplete.
Gold behaves nothing like its metallic cousins. While silver and copper,both from the same column on the periodic table,form weak oxides over time, gold remains untarnished. You might logically assume it would corrode like silver. And though gold sits next to platinum on the periodic table, it lacks that metal’s well-known catalytic properties. That is, until scientists discovered that gold nanoparticles could act as catalysts, throwing the conventional understanding into question.
Now, two researchers have proposed a fresh explanation for gold’s apparent inertness. According to their work, the metal’s reluctance to react isn’t an inherent property of the atom itself. Instead, it stems from the surfaces that gold crystals form. To understand this shift in thinking, it helps to revisit the traditional explanation for gold’s behavior,and why a supposedly inert material suddenly becomes catalytic when reduced to nanoparticle size.
Atoms and their orbital shells
Every atom consists of a nucleus surrounded by electrons. These electrons arrange themselves in a structured hierarchy, pairing up and filling orbitals from lowest to highest energy. Each orbital requires a specific number of electron pairs. These orbitals are not like neat planetary orbits; they are more like volumes of influence, sometimes spherical but often more complex in shape. The highest-energy orbitals sit farthest from the nucleus, making them the most exposed to the outside world.
An atom’s readiness to react typically depends on whether its highest-energy orbitals are partially filled. But for heavy atoms, the filling order becomes messy. Partially filled orbitals can end up buried closer to the nucleus, shielded from the environment by outer orbitals that are fully occupied with stable electron pairs. This shielding, scientists long believed, is why gold is inert: its unhappy electrons are hidden behind a wall of happy ones.
A catalytic contradiction
The discovery that gold nanoparticles could catalyze reactions revealed that this explanation was incomplete. If the inertness were truly atomic, nanoparticles would behave just like bulk gold. They don’t. That contradiction also turned the lack of catalytic activity on bulk gold surfaces into a puzzle worth solving.
(Source: Ars Technica)
