Hello students. This is going to be our first lecture on the chemical level of organization. At first, we're going to be looking at atomic structure. So, what is an atom? An atom is the smallest unit of matter. And so, remember the chemical level of organization is u is um made up of atoms. And this is what makes up all of life. And so all our cells are made up of molecules. And the molecules are made up of atoms. And understanding this will help us understand how these atoms are put together. And how the atoms put together and interact with each other determines how our molecules interact with each other and how the different molecules will work within the cell and work within the body physiologically and this will help us understand physiology. So putting all of this together is very important for us to understand the physiology of living things. And so the chemical level of organization while it is part of living things is also part of non-living things and does determine the structure and function of our organisms. And so very important in what we are going to be learning in this class. And so remember matter is anything that takes up space and um has mass. And you took a chemistry class and studied this already. So, this should be review for you. Um, keep in mind that if it's been a while since you've had your chemistry class, if you need help with this, reach out to me, come see me in office hours, give me a text, send me an email, meet with me so we can go over the things that you're you're struggling with so that we can get you caught up if it's if it's been a little while because this is very important for the rest of the class and we'll be using this every day in this class. So an atom an atom is the smallest unit of matter. It it has its own property. So when we talk about elements each element um has its own type of atom and the atoms are determined by the the particular subatomic particle specifically the number of protons. So each atom has a specific number of protons and that number of protons determines the type of element. So we'll in our next lecture we're going to talk about the periodic table and the and the different elements that are in the periodic table and that will be determined by the number of protons which is one of the subatomic particles in the particular atoms. Today we're going to look at the structure of the atom and the subatomic particles that make up the atom. So we have three types of subatomic subatomic particles that we are going to talk about and these are going to be the protons which have a positive charge. Their mass is approximately one atomic mass unit. So mass of one and they reside in the nucleus. Okay. So positively charged reside in the nucleus. Neutrons again same approximate mass about one and so they contribute to the mass of the atom like the protons and they also reside in the nucleus. So in the nucleus we have protons and neutrons together both contributing to the mass of the atom um little bit larger than the protons the neutrons are but no charge. So protons and neutrons in the nucleus and these contribute to the mass. Outside of the nucleus are our third atomic particle, the electrons. And these have very little mass. Really, really tiny. Look at this. This is four decimal places over. Very very small. Okay, really really small are the electrons. They are negatively charged. Okay. So, um, they reside outside the nucleus and they're going to surround the nucleus in levels, so to speak, and we'll talk about that in just a second, but they will go around the nucleus, orbit the nucleus to some degree, and they have a negative charge and very little mass. So they do not contribute to the overall mass to any large degree. So when we look at the atomic structure, we will find the neutrons and the protons in the nucleus here and the electrons surrounding this. So when when atoms are drawn, you usually will see the electrons out here and the protons and neutrons will be drawn in the center here. Sometimes they're drawn in the electron cloud model where you don't see the electrons here, but they will be orbiting in this cloud. And this is drawn in a 2D, but appreciate that they're they're surrounding the the nucleus in all directions, not just in in a two-dimensional way. And same thing here the electrons will be surrounding and orbiting not just in two dimensions but in all three and coming at you versus and around in all directions there. And so atoms do have a neutral charge meaning the number of protons equals the number of neutrons. So atoms unless otherwise stated are neutral. So that's important to understand. The number of protons will equal the number of neutrons and that makes them neutral. They're the the charges cancel out and there's no charge to the neutrons so they do not contribute to any charge and the neutron numbers can vary. Where do the electrons reside? They reside outside the nucleus and they reside in what we call shells. So different level levels away from the nucleus that will be the shells and they'll orbit in that level that distance away from anywhere in that space away from that that nucleus. And the first shell the shell closest to the nucleus is very small and so can only hold about two electrons. So once it holds two, it's very full and that's the maximum number it can hold. And the second shell is a little bit further away. It's further out and it can hold about eight. So it's full at about eight. The third shell being further out has more space and can hold up to 18 electrons, but is very happy and satisfied as long as it has eight. And pretty much any shell after that would be full or happy or satisfied with eight electrons. So the shells exist at levels away from the nucleus and they have a certain number of electrons that will fit in those shells. And to be satis to be full or satisfied, the first shell can carry two. the second shell can carry eight and any shell after that um is satisfied with eight. And so we call this our duet rule and our octet rule is that the first shell um can carry f is full with two and the second and thirds are full or happy with eight. Okay, note that the third shell can have more than eight, but it is satisfied with eight. Okay, and any shell after that as well. And so these are some examples of different elements. So if you note here, hydrogen has one proton and one electron and there's only one. So this first shell is not full and it has one electron. Helium has two protons and two electrons. And so this first shell is actually full with two electrons. And see here you've got carbon. It has six protons and six electrons. The first shell fills up with two. And there's four left for the second shell. Is that last is that second shell full? No. Remember the second shell can carry how many? Eight. Correct. So if if it can carry eight and there's only four in it, how many more does it need to be satisfied or full? It needs four more. Good. So this is super important in understanding the atomic in understanding the reactivity of these atoms is that they will react until they are full. So atoms want to have a full shell. So they will be reactive until they they are satisfied or until they have a full outer shell. And so carbon will react until it gets a full shell. So it will either get rid of four, which is very hard to do, or gain four electrons or share four electrons, which is more likely, with somebody else. And that way it will fill this outer shell. Another example here would be um neon. And you look here, it's got you can my head's kind of in the way, but um it's got eight in the outer shell and two here in the first shell. And that would be it has an atomic number of 10 and 10 electrons, 10 protons, 10 electrons. And it is full. So it is satisfied. So these are two elements that are the atoms are satisfied with two in the first shell and eight in the second shell and they are non-reactive because they are satisfied. So we'll talk about that throughout this course. We're going to really focus on this in our first lab in the first week. So pay attention to this. It's very important. It will determine the number of bonds that an atom forms. So understanding the number of electrons in the outer shell is very important. So, our next lecture is going to be on elements and the periodic table. And we'll really look at how these are arranged and their reactivity a little bit more. I hope to see you there.