Tutor profile: Lauren N.

What is the difference between Sn1 and Sn2 reaction?

An Sn1 reaction is two steps - you form a carbocation intermediate, then the nucleophile attacks. Therefore, the stability of the carbocation is key to this reaction proceeding. An Sn2 reaction is one step and depends on the strength of the nucleophile. An Sn1 reaction will occur most commonly with a tertiary alkyl halide; an Sn2 reaction will occur most commonly with a primary alkyl halide. An Sn1 reaction can proceed with a weak nucleophile, but an Sn2 reaction prefers a strong nucleophile.

Explain the different levels of protein structure.

There are four levels of protein structure: primary, secondary, tertiary, quaternary. Understanding these levels are key to understanding how proteins function. Primary structure is the most simple: it is just the order of amino acids that make up the protein. These are held together by peptide bonds. Secondary structure is a pattern of folded structures. There are two main ones: alpha helices and beta sheets. These are held together by hydrogen bonds. Tertiary structure is a 3D pattern of secondary structures. Tertiary structure occurs due to the different R groups in each secondary structure and how they interact. Quatenary structure is many protein subunits to make an even larger overall protein. An example is hemoglobin, which is made up from 4 subunits.

Write out the electron configuration for Calcium.

To write out the electron configuration for Calcium, you will want to know what period and what group Calcium is in. A period is a horizontal row on the periodic table. A group is the vertical row. We know that Calcium is in the 4th period and second group. I would explain to the student that the pattern for electron configuration is 1s --> 1p --> 2s --> 2p --> 2s -- 2p --> 3s --> 3p --> 4s --> 3d --> 4p, etc. I would then explain that the s orbitals are the first two groups and the p orbitals are the last six groups. Then, you just have to count out. We know that Calcium is in the 4th period, second group, so we know its electron configuration is going to end in 4s, but 4s what? Since it's the second group, it will end in 4s2. Thus the ultimate electron configuration for Calcium is 1s21p62s22s63s23p64s2.