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Quantum Mechanics: The Basics "Energy occurs in discrete bundles." By Andrew Woodward, AP Chemistry Student

Quantum Mechanics allows us to understand the structure of the atom through energy levels around the nucleus and predict the locations of the electrons inside the levels. Quantum Mechanics tells that within the energy levels (shells) are subshells and within the subshells are orbitals. This information is categorized into four quantum numbers. The principal quantum nubmer, n, has integer values ranging from 1 to in theory, infinity. As the value of n increases, the amount of energy in that level increases. Shells with large n values are farther away from the nucleus than shells with small n values. The second quantum number, l, has values ranging from 0 to (n-1). The number of l quantum values is equal to the number of different orbitals in the respective energy level. The third energy level (n=3), would have l quatum values of 0, 1, and 2. This means that there are three different types of orbitals in the third energy level (s, p, and d orbitals to be precise). Each orbital can have no more than two electrons. The two electrons in each orbital must have opposite spins (+1/2 or -1/2). This is the fourth quantum number denoted 'ms' and can have values of +1/2 or -1/2.

According to the Uncertainty Principal, it is impossible to know the location and momentum of an electron at the same time. If we know one, we cannot know the other at the same instant.

If light strikes a atom, the electrons in lower energy levels are excited up to higher energy levels and a photon is emitted. The energy of the photon is equal the difference in energy levels (the ground state to the excited state).