French Revolution Timeline May 5, 1789 A meeting of the Estates-General is called by Louis XVI in Versailles to discuss and approve a new tax plan. June 17, 1789 Three Poitevin cures decide to join the Third Estate, leaving the Chambers of the Clergy.
Helium is a chemical element with symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table. Its boiling and melting points are the lowest among all the elements.
The highest occupied electron shell is called the valence shell, and the electrons occupying this shell are called valence electrons. The chemical properties of the elements reflect their electron configurations. For example, helium, neon and argon are exceptionally stable and unreactive monoatomic gases. Helium is unique since its valence shell consists of a single s-orbital.