A mineralogy paper I read gives gold a density of 19.3 and hardness in the Mohs scale of 2.5, ie. very soft. Gold is extremely dense, yet can be scratched, dented and deformed easily. How can this be?
My medium is wood. In wood, density correlates very accurately with hardness and strength. Dense woods have more cellulose and lignin and less air within a given volume of material than light woods, and the more solid wood is, the harder it is to scratch, dent, or break it. Gold is about 20 times heavier than the densest woods, yet no harder (I have wood samples that can’t be scratched with a fingernail - that gives a Mohs value of over 2).
This is probably a very stupid question, but physics aren’t my forté. I hope to get a layman’s explanation on this.
Hardness comes from how strongly the atoms in the material are bonded to the rest of the atoms. In gold and mercury, for example, the atoms are loosely bonded even though there are many of them per unit volume and each of them is very heavy. There is no direct correlation between density and the strength of those bonds.
With wood, hardness and strength come from how much cellulose (vs. air) is packed in each unit volume, so there is much more correlation between density and strength.
because you have to look at the structure and how the molecules are bonded as well as the mass. Which of these structures is stronger:
A pile of legos
The same number of legos fastened together to form a brick
An identical brick of legos heated so the bricks are melted together a bit.
All 3 piles are the same, but the the way they are put together makes a vast difference in strength. In much the same way, different molecules will form different structures from a tight crystalline lattice to a jumbled orgy, and they will also form different bonds with each other.