Lesson 7: The Quantum Model of the Atom and Electron Configuration

The Quantum Model of the Atom and Electron Configuration

How a rat saved the world... Or something like that.

​Light and Electrons

​So, we have seen that light behaves as both a wave and a particle. Electrons have strange behavior of only existing within particular orbits around the nucleus of an atom. They also can be diffracted, or bent, like a wave can. So, could electrons have a dual wave-particle nature as well?

​Where are electrons?

​Well, we know that electrons exist in the electron cloud around the nucleus of the atom, but where are they in that cloud? According to physicist Werner Heisenberg, since electrons are located using photons (which have the same energy as an electron), electrons are knocked off of their course. This led to his proposal of the Heisenberg Uncertainty Principle which states that it is impossible to determine the location and velocity of any particle simultaneously since measuring one changes the other.

​Schrodinger Waves and Quantum Theory

​Schrodinger's Wave Equation discussed in the second video paved the way for modern quantum theory which describes the wave properties of electrons and other very small particles in mathematical terms.

Multiple Choice

True or False:

Electrons behave as a wave, not a particle.

• True

• False

​Electron Orbitals and Quantum Numbers

​This change in our understanding of electrons also changed the way we understood electrons to exist around the nucleus of the atom. Since we must predict where an electron will be found, scientists describe electrons as existing in orbitals and they describe these orbitals using quantum numbers.

​Principle Quantum Number

​The principle quantum number, expressed by n, indicates the main energy level of the electron. As n increases, the electron's energy and distance from the nucleus increases. So, an electron with a principle quantum number of n = 1 is occupies an orbital closer to the nucleus than the electron whose principle quantum number is n = 3.

​Angular Momentum Quantum Number

The angular momentum quantum number, denoted by l, indicates the shape of the orbital. These are sometimes called sublevels. Except for n = 1, there exists multiple shapes of orbitals. The number of orbital shapes possible is equal to n with the value of l being equal to

n - 1. So, for n = 3, there are 3 possible shapes: l = 0, 1, or 2.

​Angular Momentum Quantum Number

Orbitals can have up to 4 different values. For each of these values, chemists use letters to name the orbitals. They are:

​

• ​0 = s

• ​1 = p

• ​2 = d

• ​3 = f

​The shapes that correspond to the values of l

Multiple Choice

Which letter correctly corresponds to the type of orbital shown in the image?

• s

• p

• d

• f

​Magnetic Quantum Number

The magnetic quantum number describes the orientation of the orbital and is symbolized by m. The value of m can range from l to -l including integers and zero. So, for

l = 3, m can equal from -2 to 2, or, -2, -1, 0, 1, or 2 depending on which orientation of the orbital is being referenced.

Spin Quantum Number

Each orientation of each orbital can hold two electrons. These electrons are said to have opposite spin values. The spin quantum number can have the value 1/2 or -1/2. If one electron in the -1 orientation of the p orbital has a spin of 1/2, then the other electron in that same orientation of the same orbital has the spin -1/2.

​Quantum Numbers and Electrons

​The table to the right is useful for remembering how many electrons can go in each orientation of each orbital, how many electrons fit into each orbital, and how many electrons fit into each energy level.

Multiple Select

The spin quantum number can only have which two values?

• 1/2

• -1/2

• 2

• -2

Multiple Select

If n = 2, which values of l are possible?

• 0

• 1

• 2

• 3

Multiple Choice

Which orbital letter corresponds to l = 3?

• s

• p

• d

• f

Multiple Choice

How many orientations are there for all d orbitals?

• 1

• 3

• 5

• 7