General Chemistry Review
By James Ashenhurst
From Gen Chem to Organic Chem, Part 14: Wrapup
Last updated: March 21st, 2019
So what are the key concepts from General Chemistry that you need to apply to Organic Chemistry, going in? This past summer, I saw people asking this question on places like Yahoo Answers and SDN all the time. So I decided to do something about it. It was embarrassing how much 1st year chemistry I’d completely forgotten, but putting something like this together was helpful to solidify it again. If you really want to learn something, try teaching it – that goes for anything, by the way.
Anyway, from the perspective of someone going into Organic Chemistry, these are the key lessons I’d take away from General Chemistry:
- atoms are built up from protons, neutrons, and electrons, and the energies of electrons are quantized – they ascend not gradually (like a ramp) but in discrete levels (like stairs)
- electrostatic attraction and repulsion is the fundamental force that underlies all of chemistry, from the octet rule, the formation of chemical bonds, and even in determining periodic trends in properties like ionization energies and electronegativity
- there is a driving force for atoms to satisfy the octet rule, and Lewis structures are the tool we use to visualize the number of electrons surrounding each atom in a molecule.
- chemical bonding ranges across a scale from ionic character (where there is vastly unequal sharing of electrons) to covalent character (in which electrons are shared equally)
- there are important chemical behaviors called acidity and basicity and two important definitions of each – in the Brønsted definition, an acid is a species that donates a proton (H+) and a base accepts a proton; in the broader Lewis definition, an acid accepts an electron pair and a base donates an electron pair.
- thermodynamics is the study of the exchange of energy between atoms/molecules and their environment; using standard tables, we can use Hess’ law to calculate the enthalpy (heat) change for a reaction, or if tables are unavailable, approximate it by making calculations based on the energies of the bonds broken and formed. The measure of whether a reaction is favorable is the Gibbs energy, ΔG – which takes entropy into account – and as temperature is increased, the entropy factor will begin to favor processes that lead to an increase in entropy, like gas formation and fragmentation reactions.
- the rate of a chemical reaction depends on 1)temperature, and 2) the concentrations of the reactants in the slowest step of the mechanism (the rate-determining step). By studying reaction rates we can gain insight into reaction mechanisms, as well as determine the activation energy of a process.
- reactions which proceed with no net change in the concentration of reactants or products are in equilibrium. We can use the equilibrium constant to figure out the ΔG for a process using the van’t Hoff equation. Small differences in ΔG can lead to huge differences in the direction of the equilibria! We can also use Le Chatelier’s principle to manipulate chemical equilibria to drive it in the direction we desire.
Here’s a list of all the posts:
Even though I’m the world’s worst graphic designer, I could probably put these together as a PDF if enough people are interested. Hope it’s useful!