Electron Arrangement

What is an energy level again?
Energy levels surround the nucleus in layers called shell, similar to the way onion peels surround the core of the onion.  The electrons are located  in these energy levels.  The first energy level can hold only 2 electrons, the second level can hold 8 electrons, and the third level can hold up to 18 electrons.

Do electrons reside in certain energy levels?
Electrons with similar energies are grouped in the same energy levels.  Shells closest to the nucleus contain electrons with the lowest energy.  As the shells move farther from the nucleus, the electrons contain more energy.  Whenever possible, electrons will always occupy the lowest energy level first.  The majority of the time, it is only after the lower energy level is full that the electrons will move to the next level.

What about the Octet Rule?
Earlier, when looking at the periodic table, we said that electrons will be reactive until they have full outer energy levels.  BUT...the Octet Rule states that electrons will be stable when they have 8 electrons in their outer level.  How can this be when only one energy level is full with 8 electrons?
The answer is simple.  Hydrogen and Helium are an exception to the rule because their out level is full with only 2 electrons.  Atoms, such as chlorine, that have 3 energy levels, are still happy when they have only 8 electrons in their outer level.  Remember elements are lazy.  Electrons will occupy the levels with the lowest energy first.  Only after that will they move to the next level.  The third and the fourth energy level overlap in their energy values.  After the third energy levels has 8 electrons, the next 2 will jump to the fourth energy level because it takes less energy for them to do that.  The next set of electrons will then come to fill the rest of the third energy level.  This why elements are happy when they only have 8 electrons.  They are stable with exerting the least amount of energy possible.

Can electrons leave their specific energy levels?
Electrons can absorb energy from heat or light and jump to a higher energy level.  Once here, they are VERY unstable and will quickly drop back to the lower energy level emitting some energy.  We see this happening everyday.  A great example is Neon lights.  With these lights, electrons gain some energy, jump to the next level, then fall back to their original level releasing energy in the form of light. Visible light is also a result of electrons bouncing from one level to the next.  They emit this energy as light in something called the electromagnetic spectrum.

What is the electromagnetic spectrum?
This is a spectrum of all the energy emission from electrons bouncing energy levels.  As humans, we can only see a small portion of this spectrum called visible light, or better know as the rainbow.  The spectrum also includes things such as X-rays, gamma rays, infrared light, radio waves, and even microwaves.  It is easy to see with the types of energies in the electromagnetic spectrum, electrons are vital to human life.

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