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Atoms Are Built Up by Adding Electrons Although the nucleus of an atom is very dense, the electrons around it can take on a variety of positions which can be summarized as an electron configuration. An element's electron configuration can be represented using energy level diagrams, or Aufbau diagrams. The Aufbau principle (from the German Aufbau meaning "building up, construction") describes a model-building method in which an atom is "built up" by progressively adding electrons. As electrons are added, they assume the most stable shells with respect to the nucleus and the electrons already present. Filling in an Aufbau Diagram The order in which orbitals are filled is given by the Madelung rule. The rule is based on the total number of nodes in the atomic orbital, n + ℓ, which is related to the energy. In this context, n represents the principal quantum number and ℓ represents the azimuthal quantum number. The values ℓ = 0, 1, 2, 3 correspo

Copyright: wiredcosmos When you view an atom, the first question you might ask is ‘what kind of atom is it?’ What you are really asking is ‘which element am I looking at?’ You can answer this by counting the number of protons in the atom. The number of protons , neutrons and electrons is the same in a neutral atom- that is, an atom with no charge. So, in a regular Calcium atom, there are 20 protons, 20 neutrons and 20 electrons. The electrons orbit around the nucleus and have a negative charge.  An isotope is a version of the element with a different number of neutrons. When the number of protons differs from the number of electrons, you have an ionic charge. A Calcium atom with 20 protons and 18 electrons has a charge of 2+ because it has 2 extra protons, which have a positive charge. A charged atom is called an ion . When the charge is positive, it is called an cation . If the Calcium gained two more electrons it would have a charge of 2- because it has 2 extra e