Back To CourseCollege Physics: Help & Review
25 chapters | 266 lessons
Damien has a master's degree in physics and has taught physics lab to college students.
What do you think is the most important building material? Is it wood, steel, bricks, concrete, or something else? If you ask me, it's something a lot more basic than any of those materials: atoms. Atoms are the building blocks of our universe. Everything you can see and touch is made of them.
Atoms are categorized into different types called elements. Each element is defined by the number of protons in that atom. We call this the atomic number, which can be seen on the periodic table.
A neutral atom has the same number of electrons as it does protons. These electrons are what let atoms work as building blocks for everything in the universe. Neither you, I, nor any object or person you can think of in your everyday life would exist without electrons. Since electrons are so important, we'll delve deeper into learning how they are structured in an atom.
In order to see how the electrons are structured around an atom's nucleus we use something called an electron configuration. Let's dive straight in, and learn about electron configurations by looking at an example element.
In this electron configuration we have a bunch of letters and numbers raised to different powers. Each letter and number pair represents a group of electron orbitals in the atom. An orbital tells us the approximate positions in which electrons surround the nucleus. The numbers in superscript represent the number of electrons in each orbital group. The total number of electrons each group can have is determined by the letter; s can have 2 electrons, p can have 6, d can have 10, and f can have 14.
So, how do we go about filling out an electron configuration ourselves? The orbital groups are filled out in order according to Madelung's rule, which can best be visualized by a chart.
Let's try using this chart to fill out an example electron configuration for a selenium (Se) atom. Selenium has an atomic number of 34, and therefore has 34 electrons to fit into their proper orbital groups. To write out selenium's electron configuration you just follow the arrows starting at the top, and work your way down the electron configuration chart. Following these instructions we find that selenium has the following electron configuration.
We've seen how to write out electron configurations, but so far we've been glossing over what those numbers and letters in the configurations mean. We call these numbers and letters quantum numbers, and they tell us about different properties of electrons and their orbitals. There are a total of four quantum numbers. Let's go over each of them.
The first quantum number is the principal quantum number (n). This is the number we see in each number and letter orbital group pair in an electron configuration. The principal quantum number tells us two things. First, it tells us the electron's energy level, which we often refer to as its shell. Second, it tells us the orbital's size. Principal quantum numbers are represented as integers with a smallest possible value of 1.
n = 1, 2, 3, ...
Here n = 1 is the lowest energy level of an electron, also known as the ground state. Then n = 2, n = 3, and so on are excited states with higher energies. Also, as n increases so does the orbital's size.
The angular momentum quantum number (l) is the letter that follows the principal quantum number in an atom's electron configuration. We consider them sub-shells of the electron energy level shells. These letters represent the various shapes that the orbitals take.
We can find an orbital's shape if we know the value for l, which always starts at a value of 0 and goes to a maximum of n - 1.
Let's look at the example of n = 3. This means l will consist of integers from 0 to n - 1.
n - 1 = 3 -1 = 2
l = 0, 1, 2
Every value of l corresponds to a different orbital shape. Here we have l = 0 which corresponds to the s orbital shape, l = 1 corresponds to the p orbital shape, and l = 2 the d orbital shape.
Our final two quantum numbers aren't represented visually in the electron configuration. The first of these two is the magnetic quantum number (ml). This tells the orientation of an orbital around the nucleus. The number of orbital orientations depends on the electron's angular momentum quantum number. Specifically, the values for ml are integers in the range -l to +l.
For example, if we had a p orbital whose l value is 1, this would give us ml = -1, 0, 1. So there are three differently orientated p orbitals around the nucleus.
Finally, the last quantum number is called the spin quantum number (ms). Electron spin is not the traditional sort of spin you think of, such as a wheel spinning. Instead it is an intrinsic value of an electron. Electrons can either have spin up, ms = +1/2, or they can have spin down, ms = -1/2.
Spin is important because it allows the electrons to uphold the Pauli exclusion principal, which tells us that no electrons in an atom can have the same values for all four quantum numbers (n, l,ml, ms). A single orbital generally consists of two electrons with the same values for n, l, and ml. However, these two electrons will uphold the Pauli exclusion principal because they always have opposite values for spin.
Atoms consist of a nucleus surrounded by an electron cloud. The electrons fill out this cloud in a specific structure. We call this the atom's electron configuration, which consists of a series of orbitals that tell us the approximate positions of electrons around the nucleus. Each orbital group is written as a number and letter pair raised to a power. That power is the number of electrons in that orbital group. We can fill out the electron configuration for an atom by following Madelung's rule.
The number and letter pairs in an electron configuration represent two of the electron's four quantum numbers. These quantum numbers tell us more information about the properties of electrons and their orbitals.
The principal quantum number (n) tells us an electron's energy level and its size. The angular momentum quantum number (l) lets us know the shape of an electron's orbital. The magnetic quantum number (ml) gives us the orientation of the orbital around the nucleus. Finally, the spin quantum number (ms) is an intrinsic electron value. Paired electrons in an orbital always have opposite spins.
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Back To CourseCollege Physics: Help & Review
25 chapters | 266 lessons