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Energy Levels and Angular Momentum
Electrons orbit the nucleus at different distances from the nucleus much like the planets orbit the sun in the solar system. Each orbit corresponds to a different energy level and can accommodate a certain maximum number of electrons. The electrons hate energy, so they want the least of it as possible. Because the inner most orbit has the lowest energy and the next has more,the electrons first fill the inner most orbit called the first orbit. The energy level symbol is n. n takes values 1, 2, 3 etc.
The energy of the electron also depends on the angular momentum. The angular momentum symbol is l. The maximum value l can have for any particular n level is n-1. So for a particular value of n, l assume values from 0 to n -1.
l orbitals are labeled as the letters s,p,d. They can each hold a maximum number of electrons.
The angular momentum has different possible orientations labeled by m. For a particular value of l, m takes the values -l to l in steps of 1. For example if l = 2, m = -2, -1, 0, 1, 2
Each value of m accommodates at most two electrons, one of each spin type. The two types of spins are the up spin and the down spin.
For example let’s look at the distribution of electrons in the carbon atom.
By adding all the electrons that can fit in all the m orbitals for a particular n level we get the maximum number of electrons in the particular n level, which is equal to n*n*2. Like in the second level we have n = 2. We see that 2*2*2 is equal to eight therefore the second level can hold a maximum of electrons which is eight.