How protons, electrons and neutrons were discovered.

The quantum model of the atom and the electron orbital clouds s,p,d.

This Chemistry lesson is titled Valence Electrons and the Periodic Table and will give a detailed explanation of the topic.

Covering how energy in electrons is related to its position and calculated by quantum energy changes. Also covered is quantum numbers, how they are assigned, and what they mean.

This is the first in a series of video lesson on d-block elements and their compounds. I look at the electronic configurations of the first row and try to explain the trend in their melting points. Minimizing electron repulsion is the most important consideration at play in these atoms and ions, but it is not the only one. This lesson is aimed at High School level and I only attempt to provide a simplified explanation. The following three points are perhaps worth adding: (1) the 4s orbital behaves as the outermost energy orbital - and as a result they nearly always lose a minimum of 2 electrons. (2) in addition to energy levels of orbitals, you need to factor in both their shape and closeness to one another - facilitating electron movements between them. (3) atomic orbitals can mix (hybridize) and at times the actual electronic configuration of the ions may be more complex than shown here.

Scanning electron microscopy (SEM) is a powerful imaging technique which produces a largely magnified image by using electrons and X-rays instead of light. Primary electrons come from the electron gun situated at the top of the microscope. Secondary electrons originate from the specimen as a result of displacement by the primary electrons. Backscattered electrons consist of high-energy electrons originating in the primary electron beam that are reflected or back-scattered out of the specimen. SEM can be coupled with an X-ray spectrometer which is called energy-dispersive X-ray spectroscopy (EDX). At rest, an atom within the specimen contains ground state electrons. The primary electrons from the electron gun excites an electron in an inner shell, prompting its ejection as a secondary electron, resulting in the formation of an electron hole within the atom’s electronic structure. An electron from an outer higher energy shell then fills the lower energy hole, and the excess energy is released in the form of an X-ray photon. Each element of the periodic table emits X-rays at distinctive energies due to distinct elemental electronic structure. Thus, X-ray emission data can be analysed to characterise the elemental composition of the specimen and also perform area mapping.