I don't know the structure of matter, so I can't give a deeper explanation. I can only simply think that the density should be similar to the number of atoms per unit volume multiplied by the mass of a single atom. The density of various substances is different because the mass of atoms in a substance is different from the average distance between atoms (or the number of atoms per unit volume). For an extreme example, after heavy atoms are gasified, they exist in the form of gas, although they are very heavy. The number of atoms per unit volume is very small compared with solids, and its density is many times smaller than that of solids composed of light atoms.

The calculation of density should be a very complicated problem and the result will not be simple.

I found something that I hope will be useful:

Generally speaking, the crystal density of boron, aluminum, iron and platinum group elements in the middle of the periodic table is the highest, and the crystal density of elements on the left or right side of the periodic table decreases gradually, but there are many exceptions, such as some crystallization methods of fluorine and chlorine atoms improve the density, while some crystallization methods of some elements significantly reduce the density.

Why is this happening? The reason is mainly related to the change of atomic radius of elements and the bonding mode during crystallization.

Because the atomic radius of elements, whether it is * * * valence radius or metal atomic radius, is generally on the leftmost side of the periodic table, the alkali metal element is the highest, and the atomic radius decreases to the right side of the periodic table, so the crystal density of atoms will inevitably decrease from iron, platinum group elements, boron and aluminum elements to the alkali metal elements on the left side of the periodic table.

The reason why the crystal density generally decreases from the platinum group elements of boron, aluminum and iron to the right is mainly because during the crystallization of these elements, the bonding mode between different atoms will change from the tightly packed crystal bonds of metal elements in the first half of the cycle to the loosely packed molecular formula with gaps. When the elements move to the right half of the periodic table, the average spacing between adjacent atoms will be larger when the crystallization process attracts each other to form bonds.

The reason is that the electron configuration number of the outermost layer outside the nucleus of an element increases, so that when an atom crystallizes, the bonding electron orbital of the outer layer which can move eccentrically becomes closer to the electrons of the adjacent inner layer, and it is not easy to attract the bonding attraction site which can form crystal bonds with the adjacent atoms when bonding, which is caused by large deflection (see the author's paper Chemical Bonds of Elements for the specific mechanism).

Therefore, although the mass of substance atoms increases from platinum group elements of boron, aluminum and iron to the right, the density of substance atoms during crystallization decreases with the increase of bonding distance, and the bonding methods are not tightly stacked and the stacking gap is large, so that the crystal density of elements decreases with the shift of the periodic table to the right.

As for carbon atoms, when they crystallize to form diamonds, their density will increase abnormally. The main reason is that when the four outer electrons or all six outer electrons outside the element nucleus are close to each other and crystallize at a very high temperature, the motion orbits may all show strong eccentric motion characteristics, and different electron orbits may penetrate inside and outside, so that the atomic radius will be significantly reduced during the cooling process after crystallization.

However, the density of fluorine, chlorine, arsenic and other elements increases abnormally after crystallization in a certain way, mainly because the combination mode of crystallization is closer than that of adjacent elements, while the crystal density of elements other than nitrogen and arsenic becomes obviously lower because the combination mode between different atoms is looser when crystals condense.

/blog/blogshow.asp？ aid= 10 195