Okay, so we're going to talk about the smallest unit of matter, the atom. And the atom is actually comprised of subatomic particles. Those subatomic particles are found in different regions of the atom, say in the nucleus or in the orbitals around the nucleus.
Those subatomic particles are what's going to define a specific atom, otherwise known as an element. And it's also going to define how... how they come together as compounds and how molecules with multiple different atoms.
So when you're looking at the periodic table, that's what we're going to start with. And we are just looking at one specific atom. And in this case, it's helium. We notice that in the nucleus, the subatomic particles are protons that are positively charged with In the nucleus, there are also neutrons, and those neutrons are neutral. However, around the orbital of the nucleus are electrons, and those are negatively charged.
What these numbers are telling us is the atomic number specifically saying how many protons there are. And in this case, there are two protons, one, two, that are found in the nucleus. But it doesn't give us the exact number of neutrons. And that is because the neutrons can vary within the atoms or within one specific atom.
And so how you find that is you subtract the protons, so our atomic number, from our atomic mass. And that will give us a not whole number. And that is because the number of neutrons can change. and those are due to isotopes, which we'll talk about in a few slides. It's really only the number of neutrons and protons that comprise the atomic mass, and that is because the electron is so minute.
They're measured by a Doulton. You do not need to memorize this, but just so that you're familiar with it when you read it or see it in other texts. So these charges are going to have different properties.
So like charges repel, and that's why the neutrons are there to balance the amount of protons found in the nucleus. And then our negative charge, we're going to see how that's going to interact differently depending on the specific atom. Most atoms are neutral where they have the equal number of protons and electrons. So those, whenever you see an atomic number, you know that's protons, you can assume that there are two electrons also present. Unless we are an ion, and we'll talk about that in a future lecture.
Just to review, protons are positively charged, they're found in the nucleus, and they define what specific atom it is, because those numbers do not change. Protons stay the same. Versus neutrons, there's no charge. They're found in the nucleus. Those can change, and those will be specifically our different isotopes.
And our electrons are negatively charged, found in that orbital, and those are what defines chemical bonding, which we'll be talking about in future lectures. The majority of living organisms are comprised of four basic. atoms.
And those are hydrogen and oxygen, water, right? And then carbon. And that's because carbon is a backbone for all of our macromolecules.
We have nitrogen as well, because nitrogen is comprising our proteins and our nucleic acids. So 96% of the human body is comprised of these atoms alone. That's not to say that the other atoms are not important.
For example, calcium, if you have a deficiency, you can lead to things like osteoporosis. We're going to see phosphorus being involved in ATP, adenosine triphosphate, sulfurs comprising many of our amino acids. These are all essential for signaling in our body.
Furthermore, iodine. If you look at the trace elements, it's important for thyroid function. And manganese, which is my favorite because I wrote my dissertation on it, is really important for antioxidant effects. So looking at the periodic table, you can see that in the first three periods are our big six, right?
So our carbon, our oxygen, our hydrogen, phosphorus, sulfur, nitrogen, they're there. And we're going to focus on these first three rows since they comprise many of our essential atoms that we are concerned with in biology. These trace elements.
as you can see, are also very important in biology. And we will be talking about them throughout the course as well. So we had mentioned isotopes. And isotopes differ in the number of neutrons.
It's the same atom. So for example, carbon-12 has an isotope carbon-14. And that carbon-14 can be used for radio labeling. Carbon-14, this isotopes comes from our sun and can be incorporated specifically in the bonds of carbon during photosynthesis. If an animal then ingests that carbon, it gets incorporated into their body, say into their bone matrix, and a fossil then can look at the amount of carbon-14 that is present.
Give it a date, so say that it's 100 million years old, due to the decay or the half-life of that carbon-14. There are other isotopes that we can use in biology. For example, we can radiolabel glucose and those carbons that are found in glucose.
This will allow us to give a patient or a study subject. Glucose is radio labeled and look at neuronal activity. This is an area of the brain called the hippocampus.
So when doing a memory task, these patients, we can see that they have high levels of glucose used in these neurons doing that memory task. However, the study group or the experimental group are methamphetamine users. And methamphetamine...
causes neuronal death within this region of the brain. So you can see that there's not as much neuronal activity using that glucose for energy because those neurons have died. Another example is isotopes. Of isotopes are iodine, as we mentioned before, are important for thyroid function. So these radiolabeled isotopes can be used to therapeutically innervate and the thyroid when it's dysfunctioned due to the essential need of iodine to the thyroid.
So you can see here in this upper right hand picture of helium that we depict the nucleus having the protons, so the positive charge, whereas the electrons are found in the orbitals around it. So we want to get used to looking at these models, which are called Bohr models. It's very simplified. We're putting our electrons in the orbitals around the nucleus that contains the protons.
And so what these orbitals are, are going to show us where the electrons are likely to be found because electrons don't stay in one place. So our first shell, our first orbital is going to only be able to hold two electrons. Our second shell will hold eight electron pairs, or four pairs, eight electrons total.
And then our third shell will also have eight electrons. This is what's called the octet rule. And that means that those outer shells or those outer orbitals will have eight electrons. So looking at the periodic table again, remember that protons equal the number of electrons.
So now we're looking at electrons. And with hydrogen, we have one in that first shell and two filling that first shell. So we have two electrons filling that first shell.
These electrons on the far right-hand side of the periodic table are what's called noble gases. And they are inert, which means they do not create chemical bonds because all of the electrons are paired. All of these other elements and atoms are able to make chemical bonds.
And that is because they need to fill those outer orbital shells. And there's also a pattern that occurs. So notice we have hydrogen, lithium, sodium. So with hydrogen, we only have one electron. And so that one electron is in that first shell.
With our second period, we have two shells, but still there is only one electron in that outer shell. And in sodium, we have our third shell in the third period, and we only have one. So there's a pattern that emerges where all of the different rows are going to have the same amount of reactivity toward the bond formation.
You can see that again with... oxygen, right? So our first shell is full, one, two, and then we fill them up to eight, and we have two electrons that are unpaired, and that's what we see also with sulfur.
There are two electrons that are unpaired. So with that, that's our first section of material. You should be able to go through that recap and answer some of these questions so that you retain the information.