2.1 Electrons in Atoms

In this lesson we will delve into how electrons are bound and behave in atoms including simple models such as the Bohr atomic model and more advanced ways of thinking and representing electrons in atoms, which we call orbitals.

The Concept of Quantisation

All chemical bonds and reactions require the transfer, sharing and/or movement of electrons. Therefore, we need to know where the electrons are and what they are doing. The theory we use to describe this is quantum mechanicsThe theory used to describe the behaviour of very small particles (atomic and subatomic level). Unlike classical physics which is deterministic, quantum mechanics is a probabilistic theory., which predicts that the energy of an electron in an atom or molecule is restricted to a specific set of values; the energy is said to be quantised.

The concept of quantisation might feel counterintuitive. However, in theory, everything in the universe is quantised. But with increasing mass of an object the gap between the energetic states an object can find itself in becomes smaller and smaller. As such, in everyday life where objects are comparatively heavy, quantisation is not apparent, and traditional mechanics can be used to describe everyday objects and observations. As a rule of thumb everything that is heavier than a single atom can usually be described using traditional mechanics. Hydrogen, as the lightest atom, is a borderline case. Subatomic particles such as protons, electrons and neutrons can no longer accurately be described using traditional mechanics and require quantum mechanics.