Question

How is an atomic model useful?

Answer 1

Recall that atoms are one of the basic elementary constituents of matter. In such a case, it is safe to say that atoms define the properties of the matter that they constitute. Atomic models, on the other hand, describe the structure of the atom itself based on theoretical predictions and experimental observations, which are subject to change due to the constantly evolving science. To this end, determine the utility of atomic models and how they were used to build bridges between theory and observations throughout history.

Complete answer:
We know that an atomic model is essentially a scientific theory that describes the intrinsic structure of the basic constituents of matter that we call atoms. An atomic model thus enables us to visualize the arrangement of the constituents of an atom which in turn helps us in predicting the properties of matter that they make up.
There have been a variety of atomic models throughout history before which the currently accepted model was curated, five of which shall be discussed here.
John Dalton’s atomic model proposed that all matter is made up of tiny indivisible particles called atoms. Though matter is made up of such tiny particles, it was not necessarily true that they were indivisible constituents, as evident from the subsequent discoveries of subatomic particles like neutrons, electrons and protons. J.J Thomson’s atomic model suggested that an atom is neutrally charged and consists of negatively charged electrons embedded into a positively charged sphere. His theory was proved wrong by Rutherford’s experiments that suggested that an atom consists of a centrally located positively charged nucleus around which negatively charged electrons orbit. Rutherford’s model could not explain the stability of the atom since electrons in a circular orbit undergo acceleration and eventually lose energy and fall into the nucleus, obliterating the atom. This problem was later solved by Bohr’s atomic model which suggested that electrons move in circular orbits of fixed size and energy with no loss of energy.
Finally, collective efforts of various scientists brought together the electron cloud model of the atom, which is deemed to be the most realistic atomic model till date. This model suggests that all electrons can be perceived as matter waves with a wavelength. The electron paths are not specifically defined like in the previous models but are represented by a probability of their occurrence, meaning that their position cannot be calculated with complete accuracy. These probabilities are described by four quantum numbers that define the characteristics of the electrons and their orbitals.
Thus, the progressive study of atomic models poses an opportunity for us to scrutinize the limitations of various models and understand why certain theories did not corroborate with experimental observations. It then becomes necessary to understand the improvements inculcated into succeeding atomic models, following an understanding that is consistent with contemporary theories and observations. To this end, atomic models are an efficient scientific approach towards understanding all matter and the properties that they entail.

Note:
We mentioned that four quantum numbers describe the electrons and their orbitals in the quantum mechanical model of the atom. It is important to understand what they are.
The principal quantum number$\;(n)$ describes the energy level of the electron in an atom and has positive whole number values (1, 2, 3 ….) indicating the (K, L, M, ….) shells of an atom.
The angular momentum quantum number$\;(l)$ describes the shape of the orbital and indicates subshells or orbitals (s, p, d, f, g) constituting a shell in an atom corresponding to its values ranging from [0, n-1].
The magnetic quantum number $(m_l)$ indicates the number of ways the orbitals can be oriented in space. Its values range from [-l, +l]
The spin quantum number $(m_s)$ describes the electron spin direction in a magnetic field that can be either clockwise or anticlockwise and thus possesses one of two values: $-\dfrac{1}{2}$ or $+\dfrac{1}{2}$. Note that two electrons occupying the same orbital must have opposite spin.