In 1913, Niels Bohr developed his famous atomic model. In this model, electrons rotate in circular orbits around the nucleus, occupying the lowest possible energy orbit, or the closest possible orbit to the nucleus.
However, the popular idea of an atom is, to a certain extent, a schematic distortion, a model of understanding for laymen... an approach that bears little or no resemblance to reality. Atoms are not as they are drawn in textbooks. In fact, atoms are far from all the same: They differ greatly from each other.
Densities and shapes
As explained Santiago Alvarez in the book Of women, men and molecules, the density of atoms can vary by two orders of magnitude from one element to another, more than the density of the Earth varies from the crust to the core:
If we calculate the densities of the electron cloud and the nucleus separately, in the case of helium we find values of 2×3 10
17and 3.52 x 10-5kg/m3, respectively. That is, the density of the nucleus is about 10twenty-onetimes greater than that of its surrounding electrons. We do not have references in the everyday world to gauge the meaning of these densities. Not even the air in the stratosphere has a density as small as that of the electron cloud. We would have to go up to the thermosphere, about 100 km above the Earth's surface, to find a comparable density. In the case of the core, only a neutron star has such a high density, surpassed only by that of black holes.
Nor are atoms always spherical.. And even less is an atom within a molecule spherical. Even atoms of the same element can differ in a series of attributes:
- Number of neutrons (in different isotopes).
- Number of electrons (in multiple oxidation states).
- Degree of pairing of electrons (in various spin states).
- Variable molecular environment in coordination number and stereochemistry that also affects shape and size.
Thus, we could affirm that the invariant property between the atoms of the same element is its atomic number (number of protons in its nucleus), the property that defines a chemical element, despite the fact that the chemical reactivity and its ability to Bond formation resides in the valence electrons.
Various atoms and molecules as shown in A New System of Chemical Philosophy by John Dalton (1808).
In this way, the writing of Margaret Lucas Cavendish, Duchess of Newcastle, in her book Poems and Fancies (1653):
- Pointed atoms make the Fire subtle, fast and dry,
- The Long ones fly like arrows in the air,
- The Round ones become water, moist,
- The Squares on Earth, with immovable Form;
- Square atoms make up hard Minerals,
- Soft vegetables appropriate round atoms.
However, we need models to understand reality, because reality is not understandable in its entirety:
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The news
The density of different atoms can vary more than the density of the Earth's crust and nucleus
was originally published in
Xataka Science
by
Sergio Parra
.