Quantum Numbers

Every electron has four quantum numbers:

1. Principle Quantum Number: the same number as the principal energy level.

2. Angular Momentum Quantum Number: determined from the sublevel; 0,1,2,3 for s,p,d,f.

3. Magnetic Quantum Number: runs from -1 to 1.

4. Spin Quantum Number: 1/2 for the first electron in an orbital and -1/2 for the second.

Examples:

Assign quantum numbers for each electron:

*4d3 = (4, 2, 0, 1/2)

*2p1 = (2, 1, -1, 1/2)

*1s1 = (1, 0, 0, 1/2)

Determine the electron for each quantum numbers:

*(3, 2, 0, -1/2) = 3d8

*(2, 1, 1, 1/2) = 2p3

*(4, 3, 0, 1/2) = 4f4

Electronic Structure

There are four levels of organization to describe the location of an electron in any atom:

1. Principal energy level: How far away from the nucleus an electron is (n).

2. Sublevel: There are four different sublevels called s, p, d, and f. They are shown here:

Source of above picture

3. Orbitals: The s sublevel has one spherical orbital. The p sublevel has three dumb-bell shaped orbitals. The d and f sublevels have five and seven orbitals, respectively, and are complexly shaped.

4. Spin: Each orbital can hold two electrons of opposite spin, one upward and the other downward.

There are rules for placing electrons:

1. Aufbau Principle: Electrons enter the lower energy orbitals first.
2. Pauli Exclusion Principle: An orbital can only have two opposite spinning electrons.
3. Hund's Rule: In a sublevel, electrons must enter singly and then pair up.

Here is a website that explains these rules more in-depth: Electron Placing Rules

Spectroscopic Analysis Lab

A few days ago, we completed a super easy lab where we did the spectroscopic analysis of Cr3+ and Co2+. We got to use a really cool and high-tech piece of equipment, called a spectrophotometer. I had never used this before, so it took a couple minutes to get myself acquainted with what each of the buttons/knobs did, but once I did that, the lab was a piece of cake. Using the machine, we tested solutions of both of the elements from a wavelength of 375-625 nanometers. Here is a website that I found to explain how a spectrophotometer works: Spectrophotometer

Here is what the machine that we used looked like:

Flame Test Lab

Around a week ago in chemistry class, we started off this new unit by doing a lab where we burned different solutions and determined the wavelengths of those solutions, based off of what color the flame was. Here is the website that I used to accomplish this: Wavelengths

This lab was very simple to carry out, considering all we had to do was burn each of the solutions, which were pre-prepared for us. However, this lab was definitely one of the more interesting ones that we have done. I had no idea that flames could turn hot pink or bright green! We also looked at some of the flames through cobalt glass, which made it even easier to differentiate between the colors of all of them. Overall, this lab was very interesting and also helpful, because the conclusion made us practice calculating energy, given wavelength, which was actually on our quiz that we just took the other day. Here is a website that I found to explain how to do this calculation: Finding Energy

Here is what the flame looked like when we tested LiNO3:

Molar Mass of an Unknown Acid Lab

Last week in chemistry class, we completed our third and final acids and bases lab to determine the molar mass of an unknown acid. In order to be able to do this lab, we had to write our own procedure. First, we added 100mL of NaOH to our buret and then mixed around .5 grams of KHP with water in a flask. After the KHP was dissolved, we added 3 drops of phenolphthalein to act as our indicator. Then we titrated this using the NaOH in the buret, until the solution turned and stayed pink. Then we recorded how much NaOH was used. After this, we repeated these same steps, but with around .2 grams of the unknown acid in our flask, instead of KHP. In order to get the unknown acid to dissolve in the water, we had to heat/stir the solution at the same time. This was a new experience, because we had never used an automatic stirrer before. Overall, this lab was interesting and a good conclusion to the unit using everything that we had learned.

Here is what the solution looked like on the hot plate as we were heating it:

Water as an Acid or Base

The H+ ion in water is just a proton and they form clusters. The simplest cluster is H3O+, and is called a hydronium ion. Larger clusters can also occur, like H5O2+ or H9O4+. Water is amphoteric because it can be an acid or a base, Water can be an acid because it donates protons, it can also act as a base because it accepts protons to form hydronium ions. Pure water auto-ionizes by the following equation:

For more help with understanding the auto-ionization of water, I found this website: Auto-Ionization

Titrations and Buffers

Titration is a technique that helps determine concentration of an unknown acid or base. The reactions are called neutralization reactions, but don't actually form neutral solutions.

When titrating, the solution in the buret is the titrant and it always has a known concentration.

This solution then is combined with a solution called the analyte, which has an unknown concentration.

To know when the chemical reaction is complete, look for a color change in the analyte due to an indicator that is pH sensitive.

Once the analyte changes color, the endpoint has been reached.

Given all of the volumes and concentrations that we know, we can then calculate the concentration of the unknown.

Percent Acetic Acid in Vinegar Lab

Last week in chemistry class, we completed a three day lab to determine the percent of acetic acid in vinegar. In order to be able to do this lab, we had to memorize the procedure. First, we added 100mL of NaOH to our buret and then mixed around .5 grams of KHP with water in a flask. After the KHP was dissolved, we added 3 drops of phenolphthalein to act as our indicator. Then we titrated this using the NaOH in the buret, until the solution turned and stayed pink. Then we recorded how much NaOH was used. After this, we repeated these same steps, but with vinegar in our flask, instead of all water. This lab was really interesting, and it was a challenge to try and get the solution to turn pink without making it too dark. Here is a website that I found that explains how titrations work: How to Titrate

This is what it looked like when the NaOH reacted and started to form a pink color.

This is what the solution in the flask looked like after we were done titrating and it was staying light pink.

This is what the whole funnel/buret set-up looked like.