Chemistry Reference
In-Depth Information
FIGURE 2.3
Electrons rotate around the nucleus like planets around the sun.
most of the chemical transformations. The most common model of the atom is the
classic model imagined by Rutherford-Bohr, also known as the
solar system model
(Figure 2.3). This model is a graphic representation that is similar to the real repre-
sentation of an atom, but it is not identical to the atom; however, it is very useful for
viewing and explaining different chemical phenomena.
From this representation it can be seen that, unlike the solar system where on an
orbit only one planet is rotating, in an atom an
orbital
(orbit) is in fact an electronic
level or electronic layer capable of hosting a certain number of electrons, as repre-
sented in Figure 2.3. Each level has a certain energy and is placed at different mean
(median) distances from the nucleus. Because of the energy that the electronic layers
carry, they are also called
energy levels
.
The electronic structure of the atom is the key to understanding the properties
of the elements, of the compounds that they form their chemical reactions, and the
molecules that they shape.
The electrons, similar to protons, are electrically charged particles. Their
charge is the same size as the protons, but is negative. The number of electrons in
an atom is the same as the number of protons, so that an atom is neutral from an
electric point of view. The mass of an electron is 1836 times smaller than that of
a proton, and this is why in chemical calculations it is usually not considered (it is
neglected).
In his wave mechanics studies, Erwin Schrödinger used mathematics to assess
the probability that an electron will be in some point in the atomic space. The
mathematical relationship that expresses this is similar to the equation used to rep-
resent wave propagation in acoustics. Thus, the motion of the electron, the prob-
ability of finding it in a certain position within the atom, is characterized by a wave
function ψ or orbital that actually indicates the charge density or electronic cloud.
The Heisenberg uncertainty principle shows that it is impossible to know the exact
position of an electron at a certain point in space at a certain moment in time. In line
with this principle, the probability that an electron would find itself at a certain point
in space at a certain moment in time is given by the square of the wave function ψ
2
.
The internal motion of the electron around the nucleus is calculated according to the
Schrödinger equation:
2
µ
∇ψ+ψ=ψ
(2.1)
2
−
VE
