Question

How did quantum mechanics change our understanding of atoms?

Answer 1

Hint : Quantum mechanics, science dealing with the behavior of matter and light on the atomic and subatomic scale. It attempts to describe and account for the properties of molecules and atoms and their constituents like electrons, protons, neutrons, and other particles such as quark and gluons.

Complete Step by step explanation:
Step 1: classical Bohr’s model for atoms was having a problem that it treated electrons as particles that existed in precisely-defined orbits. De Broglie described that the behavior of electrons within atoms could be explained by treating them mathematically as matter waves. It was also concluded that there are only certain allowable states or energies that an electron in an atom can have is similar to a standing wave.
Step 2: We can think of electrons as standing matter waves that have certain allowed energies. Schrödinger formulated a model of the atom that assumed the electrons could be treated at matter waves. Also, Heisenberg’s uncertainty principle says that we can only determine the position or energy of the particles at once.
Step 3: with the help of quantum mechanics we could understand the orbitals better like their shape, probability density, etc. the shape of orbitals, s-orbital, has a spherical shape, p orbital has dumbbell shape, d orbital has dual dumbbell shape, and f orbital has a triple dumbbell shape in an atom. The electrons are supposed to be present in these orbitals in the form of a cloud. The probability density tells us how probably an electron is present at a particular position at a particular moment.
Step 4: we could understand the spin of an electron in a particular orbit, which can be clockwise or anticlockwise. And are represented by $ + \dfrac{1}{2}$ and $ - \dfrac{1}{2}$ for a clockwise and anti-clockwise spin.

Note: the theory of quantum mechanics doesn’t say whether an electron is a particle or wave. It depends on the observer how the electron is observed. In an experiment the electron can show particle-like properties on the other hand the same electron can show wave-like properties.