The Current Atomic Theory
We many times imagine the atom in our minds as either the 2-dimensional picture we
were often shown in textbooks, or perhaps the 3-dimensional one similar to a gif. that has the
nucleus with a bunch of tightly packed spheroids, and more spheroid electrons dancing
around the nucleus in neatly organized and evenly distributed orbits. This is the Bohr atomic
model which was developed in 1913 by Neils Bohr (scientists really know how to get
creative in naming things).
The Bohr atomic model is based on the pattern of the solar system - the Sun in the
centre and the planets occupying only their orbits which stayed the same orbiting the sun,
which is why it is also known as the planetary model. Each of those orbits has an energy
associated with it and energy is either absorbed or released when one of the spherical
electrons goes to a higher or lower orbit. He figured this out by calculating the energy and
frequency of light produced or absorbed by using the difference between the two orbital
energies that the electron jumped between.
The orbits of the Bohr atomic model are circular and because a circle can be defined
using only it's radius it is only one-dimensional and even our solar system is a bit more
complicated than that. Even electrons don't behave themselves like the neat little balls we like
to imagine them as, they behave in many ways like waves and are thus 3-dimensional. This
image that we have works great when learning about chemical bonding but does not account
for the behaviour or distribution of electrons in more complex atoms, we need a 3dimensional model for that.
Erwin Schrödinger, the guy who successfully made a cat both exist and not exist at
the same time, figured out that electrons behaved like waves and not like balls. He used two
equations, the one for the behaviour of waves and the de Broglie (it's not pasta) equation to
make a mathematical model to show or rather describe the probability of the electron
distribution in an atom.
Schrödinger's model is much more realistic and true and was built on the knowledge
and application of Bohr's model and now we have a way to determine if there is the
probability of an electron wave at a particular time in a particular place.
Sources:
Development of Current Atomic Theory
https://chemed.chem.purdue.edu/genchem/topicreview/bp/ch6/bohr.php#bvsreal