Density mutha fucka!
this post was submitted on 22 May 2026
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Density. Ultimately everything is made of the same quarks, but there may be more atoms per cubic centimeter in some materials vs others (think water vs steam - water is the same molecules packed much more tightly). And on top of that, some atoms just have more protons and neutrons in them - gold has an atomic mass of ~197, while copper is only ~63. So an atom of gold takes up roughly the same space as an atom of copper at a large enough scale, but has over 3x the mass.
Also, an atom is mostly empty space. So there’s lots of room for an atom to increase its number protons/neutrons without increasing its size.
At that scale what is and isn't "empty space" gets a little hazy.
If you zoom in far enough, there's always some bullshit going on.
Well... Empty empty, I don't think so; think about the whole issue of vacuum energy and the consequent virtual particle-antiparticle pairs, or the mere fact of the existence of quantum fields that permeate everything — like the field responsible for mass itself, the Higgs field.
That's a simplification; a useful one, but a simplification nonetheless.
It seems so simple, but it's pretty damn crazy when you think about it for more than like a second or two.
I’m on ten seconds of thought now and I am FREAKING OUT
You should write a song about it, it would be a great hit.
First, the measurements of volume, weight, and mass are different. This is important.
Volume is the amount of physical space something takes up. It's measured in cubic metres (as well as litres, gallons, etc. for liquids), like the units you have given.
Mass is the inherent property of matter, while weight is the force applied to a mass by the Earth's (or some other large body, like the Moon's) gravity. On Earth, weighing scales measure in Newtons, weight, but do conversion to give you conventional grams and kilograms, units of mass. Mass is the property of matter, while weight is the force produced by gravity.
Density is, in a nutshell, mass per unit of volume. Water is around 1000 kg / m^3, meaning there is 1000 kilograms of mass for every cubic metre of water. Different materials have different densities, and this is because of all sorts of things. The atoms might be very tightly bonded together in a lattice, like in many metals. This is why metals are usually very dense. While they could also be free-floating molecules with very weak attractions. This is why gases are not very dense.
In the case of gold vs copper, the former has much larger nuclei with much more protons, and that probably contributes to an increased amount of attraction in the metallic lattice, making gold denser than copper. This means the gold will be heavier than the same volume of copper.
It's not just about the number of protons though! The configuration of electrons is also very important, arguably more so than proton number. For instance, osmium and iridium are both denser than gold, but they have smaller nuclei. Electron shell shenanigans are everywhere in chemistry!
The why of mass is "just" more material within the same unit area.
What always gets me is how adding one more of the pieces of matter, specifically another proton, changes the very properties of that atom, sometimes dramatically.
A lot of what makes the elements different is the electronic configuration, which is probably more important in chemical interactions compared to proton number.
For instance, chlorine has 7 outer shell electrons and readily accepts an additional electron. This makes chlorine very reactive! In contrast, the next element, argon, is a noble gas that rarely reacts with anything. So much so, it's often used in experiments where chemicals should not be in contact with oxygen. This is because it has a full outer shell, so it doesn't readily react to create compounds. The addition of a proton also means (for a neutral atom) an additional electron, and this can drastically change the properties of an element!
Electron configuration is what mainly governs chemical processes, so differences in the chemical nature of elements is often due to the difference in electrons and their energy levels!
Since the question was already answered quite well, here's this:
What's heavier, a kg of steel or a kg of feathers? (YouTube link)