Atomic Shapes and Properties
The octahedral layout of the atoms explains the different properties of metals. The elongation of the atom of a metal is in direct correlation to its solidity. For example, Titanium atoms are flatter then the atoms of the other metals, this is why titanium is the most solid metal in our list. Mercury is a liguid metal which leads to the conclusion that the mercury atom is extremely elongated.
The structure of mercury has only little resistance compared to other metals. If we look at the structure, it becomes obvious that it must be flexible and easy to bend, and even to separate. If we take a needle and pierce the structure from above, it will drive through the entire structure without serious resistance. If we drive the needle sideways through the structure, it will slice it easily.
Whole different story with titanium - the horizontally aligned structure made up of flat atoms provides a high resistance to the metal. If we poked the structure with a needle from above, we wouldn't be able to penetrate the structure. If we poked it sideways, we couldn't slice through it due to the much stronger attachment of the atoms.
Iron is less resistant than titanium and more resistant than mercury because the atomic shape of the iron atom is more elongated than that of titanium and less elongated than that of mercury. Although iron is considered a solid metal, it's still relatively flexible and relatively easy to bend. If we tried to penetrate the structure with a sharp item, we would experience resistance, nevertheless, we would be able to drive through the upper layers due to the more elongated shape of the iron atom.
Gold is a relatively flexible metal. It's easy to bend and to scratch. If we take a look at the atomic structure of gold, we can see why gold is a softer and more flexible metal than iron - the atoms of gold are more elongated than those of iron.
Lead is another soft metal and is even more flexible that gold. While the lead atom has about the same atomic mass as gold, the lead atom is more elongated. Looking at the structure of lead, we get a sense why this metal is so easy to bend and to penetrate.