Your Organic Chemistry professor expects that you remember everything you learned in General
Chemistry but I'm guessing you don't. And so in this Leah4sci video we'll do a quick review of
General Chemistry topics that you need for Organic Chemistry. Starting with the Atom.
In the center of your atom you have a Nucleus and in that nucleus you have protons with a
positive charge that I'll show as a plus and we also have neutrons with a neutral or no charge
which together combine to give us the mass of the atom where both the proton and neutron
are each one atomic mass unit. Outside of the nucleus we have electrons which are negative
floating around not randomly but rather in specific shells and orbitals. Electrons have
such a tiny mass compared to a proton. And neutron that for the sake of this discussion, we'll assume
it's approximately zero atomic mass units. Organic Chemistry is based around the element Carbon which
you'll notice has a number 6 for the atomic number telling us that it has 6 protons and a charge of
plus 6 in the nucleus, a mass of approximately 12 amu for 6 protons and 6 neutrons and because
the atom is neutral we assume that electrons equals protons for a total of 6 electrons.
Electron location is not random, instead they exist in specific orbitals which in general
chemistry you learned s, p, d, and f. Luckily in Organic Chemistry we're only looking at the s and
p orbital. Since electrons live in the different shells. Only the outermost or Valence Electrons
are available to interact with other atoms and only those electrons are going to participate
in Organic Chemistry reactions. Those valence electrons are located in the s and p orbitals.
If you're excited to drop the rest, make sure you give this video a thumbs up and let's continue.
No discussion on atoms is complete without a look at the periodic table. Let's review only what you
need to know. This block here is our S block for the s-orbital, here we have our P block,
our d block, and f. The important groups on the periodic table are 1 and 2 for our metals, 3,
4, 5, 6, 7, and 8 for the nonmetals. This also tells us the number of valence electrons
which is how you will know that sodium has 1 valence electron, carbon has 4,
and the halogens have 7. The table also shows you some trends, the two trends to remember
are that electronegativity increases up and towards the right and size increases
down and towards the left. This tells me that Fluorine is more electronegative than Chlorine,
while Iodine is larger than Bromine. While you should get a periodic table on your Orgo exams
I highly recommend memorizing the following ten atoms. Hydrogen, Carbon, Nitrogen, Oxygen,
Phosphorus, Sulfur, and the Halogens, Fluorine, Chlorine, Bromine, Iodine.
Use my active writing approach to memorize it so that you can easily write Hydrogen, Carbon,
Nitrogen, Oxygen, Fluorine, Chlorine, Bromine, Iodine, Sulfur, and Phosphorus. Remembering that
this is 1, 4, 5, 6, 7. Electronegativity up towards the right, and size down to the left.
Atoms have a specific arrangement of electrons and in my electron configuration video linked below
at leah4sci.com/IntroOrgo, I show you a periodic table trick where you can easily
tell the electron configuration for chlorine by doing this. 1s2, 2s2, 2p6, 3s2, 3p5.
Back to the atom. Even though they start with different numbers of valence electrons, they still
want to follow the Octet rule to have a complete shell of 8 electrons. A few notable exceptions
include hydrogen which is okay with just two, boron just three, and larger atoms like Sulfur,
phosphorus, Chlorine, Bromine, can have more than 8 such as 10 or even 12 which I'll show you when
we look at Lewis structure. Bonding is how they achieve that octet. A covalent bond is when atoms
share electrons and we have two types, a polar bond is when they're pretending to share but one
of the atoms is hugging the electrons such as what you'll see between Oxygen and Hydrogen in water.
When Oxygen is hugging the electrons and pulling them towards itself, it becomes slightly more
negative making hydrogen slightly more positive giving us a dipole meaning a partially negative
end on Oxygen and partially positive end on Hydrogen. A nonpolar bond is when the atoms are
sharing the electrons equally such as Methane which has a bond between carbon and hydrogen,
very close in electronegativity and they're each holding the electrons equally. Of course when the
atoms no longer want to share you have an ionic bond which is the attraction of opposite charges.
You'll see this often in Organic Chemistry where a spectator ion like Sodium or Potassium
will be attracted to something negative like an Oxygen in this case Hydroxide. When the positive
and negative attract you get that ionic bond so that this compound is written out as NaOH
pretending to be neutral when in reality it’s Na+ and OH- . Most of the Organic molecules you study
will have covalent bonds and since bound atoms make molecules we have to know how to draw the
molecules. Lewis Structure is when you simply draw the atom, draw the electrons and put bonds between
them. For example, Methane, we have carbon and 4 hydrogens. Each hydrogen has its one valence
electron, carbon had 4 valence electrons and that allows us to form a bond between carbon
and each Hydrogen atom. But Organic Molecules are not flat, they're 3-dimensional and this comes
from understanding how the hybrid orbitals work together. Hybridization is a tricky topic and I
do cover this in detail in the series linked below or on my website, Leah4sci.com/IntroOrgo. But as
an overview, we said that the Organic Molecules have their valence shell in the S and the P
orbital where specifically we have 1 s-orbital and 3 p-orbitals. As you can see here, if every
orbital holds 2 electrons we have one pair of s electrons and 3 pairs of p to give us px,
py, and pz. The Hybridization comes from mixing them together in different quantities and all
you do is count what you see. If I mix 1 s plus 3p giving me s times p times p times p for sp to
the third or sp3. If I mix just 1s and 2p, I get sp2, allowing for double bonds or carbocations.
And if I mix just s and p to get an sp orbital I now have room for a triple bond or 2 double bonds.
In my Hybridization video I teach you that when a molecule has 4 groups around it such as Methane,
you simply count 1, 2, 3, 4, sp1, p2, p3 but this also works for water which has 1, 2, and yes
3, 4 groups around it. If a molecule only has 3 groups around it such as BH3, you count 1, 2, 3,
sp1, p2 or even the Oxygen in Acetone or Propanone has 1, 2, 3. And finally if I look at the carbon,
in carbon dioxide I have 1, 2, 1, 2 for an sp hybrid. If you want to describe the structure,
an sp3 hybrid is a tetrahedron or tetrahedral with a bond angle of approximately 109.5
so that methane molecule we kept drawing flat is better off being drawn like this,
where these two bonds are in the plane of the page, they sit flat on the screen, the dashes
are going back into the page into the screen and this wedge is coming out at you out of the screen.
An sp2 hybrid is trigonal planar or 120 degrees. Such as our acetone molecule,
this is approximately 120 and our sp hybrid is linear with a bond angle of 180 degrees.
As you can see with carbon dioxide where the molecule is drawn on a straight line.
Now that you've refreshed the basics, here's my challenge to you.
If all of this was just a review, test your knowledge using the free practice quiz on my
website linked below at leah4sci.com/IntroOrgo. And if you feel you need a more in-depth review
for any of the topics discussed today, first, give this video a thumbs up, subscribe to my
channel and hit that bell notification icon so you don't miss out on any new videos,
then see my both of my playlists linked below, also on my website at leah4sci.com/IntroOrgo.