... electron cloud. For the electronic configuration of an atom, it is imagined that the particular atomic nucleus is surrounded by empty orbital into which the electrons are occupied in order of increasing orbital energy, starting with its orbital. However, the relative energies of orbitals often change from one atom to another, and even from one atom to its ions due to the complex interaction. In other words, each atom or ion has a unique set of orbital occupied by electrons. The energy of all orbitals decreases as the charge on the nucleus increases. Besides , all orbitals in the same quantum shell have the same energy in the case of the hydrogen atom, but not in the case of a multi- electron atoms . And the main difference between the elements from neon and calcium, and those heavier than calcium, is that in the former case the 4s orbital is ...

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