I remember purchasing a leash chain sometime back for my brother’s dog but when he got back, he just abandoned the chain and went for another type that he liked which I also liked. Recently, I went back to the chain, and I saw it had changed color and rusted but this was not the same with my mum’s gold jewelry that has been with her for years even before I was born. So this birth the question, why do some metals still shine even after many years?
When we talk about the shining properties of metals, we are looking at how the metal reflects light. These metals can bounce light due to their smooth, and uniform surfaces which is actually associated to how the electrons of metals behave. Metals are made up of a shared pool of electrons that move freely throughout the structure giving the metals the ability to conduct as well as reflect light.
The electrons in metals are excited when light heats their surfaces and so the energy is released as light that is reflected. While a lot of metals are shining at the beginning, they start to lose their shining properties over time as a result of reacting to environmental factors and compounds like oxygen, sulfur, water, or moisture which leads to corrosion. When these surrounding compounds react with the metal, a dark surface is formed around the metal surface which is what you see in metals like iron that rust, or silver that turns black.
When the metals react with environmental factors, their surfaces change and so dies their chemistry leading tothe gathering of light rather than the reflection of light. So how do some metals stay shining all round? They do so by resisting the chemical changes that come with the reaction to the environmental factors.
These metals are known as Noble metals. They are known for their ability to resist corrosion, which is so because these metals are reluctant when it comes to reacting to other elements. Metals in this category as palladium, Gold, Rhodium, and Platinum. Silver is very low when it comes to the list of noble metals. These metals have extremely low reactivity making it difficult to react to elements in our environment like oxygen, sulfur, and even water. These metals resist oxidation and this is why that gold coin your great-grandparents buried in their backyard didn’t tarnish even after all these years.
Noble metals at the atomic level form surfaces that are dense and smooth. Silver is a noble metal, but it is the least noble of all the metals and so it js much more reactive than the other members of the group and so it tarnishes easily when exposed to sulfur containing content giving silver sulfide as the aftermath reaction which is the dark layer on the surface of the metal. When silver has this dark surface, it doesn’t mean the metal is gone, the dark layer just covers the shine of the metal underneath and with proper polishing, it can be restored.
After learning about this, I could understand why my mum’s gold jewelry remains the same for years while the dog iron chain loses its color quickly. So the next time I see any of the noble metals, I can be sure that they will be truly noble to their name and keep shining forever.
Read More
- https://pmc.ncbi.nlm.nih.gov/articles/PMC7960878/
- https://www.practically.com/studymaterial/blog/docs/class-8th/chemistry/metals-and-non-metals/
- https://www.sciencedirect.com/science/article/abs/pii/B9780128034101000098
- https://www.sciencedirect.com/topics/physics-and-astronomy/noble-metal
- https://sciencenotes.org/noble-metals/
- https://www.intechopen.com/chapters/60006