 Hey everybody, Dr. O here and this video we're going to talk about atoms. So I like to call atoms the basic unit of matter, right? The entire physical world which is made up of matter is made up of these atoms and then these atoms form together to form every chemical that we have. How these atoms behave determine which chemical reactions occur and which chemicals we have in our physical living world. So I already called it the basic unit of matter but the textbook definition of an atom would be the smallest quantity of an element that retains the unique properties of that element. So here we see helium and atom of helium is the smallest amount of helium that can exist. So that's how you would define what an atom is. Now atoms as you can see here are made of subatomic particles and the three that we talk about are protons, neutrons and electrons. So protons are positively charged and in the nucleus in the center of the atom in the core. Electrons are negatively charged and they're going to be in a cloud on the outside of the nucleus and neutrons are neutral and they're also in the nucleus. So remember P for P protons positive and for N neutrons are neutral meaning they don't have a charge and then electrons are the negatively charged subatomic particles. As far as weight go protons and neutrons make up the mass of an atom. So if you look at the mass number of an atom it's going to be the number of protons plus the number of neutrons. Electrons are so tiny it takes about 2000 electrons to equal the weight of one of the protons or neutrons so they're not they're not counted in the weight. I already mentioned the protons and neutrons are stay there in the nucleus the electrons they were around the outside of the nucleus and they they spin or were around it at nearly the speed of light in what's called an electron cloud. So the key thing I will say and I'll say this in several videos the key thing I want you to know about atoms is what happens if you change any of these three ingredients. So an electrically neutral atom most atoms are going to have the same number of protons neutrons and electrons. If you change the number of electrons you will have given this this atom a positive or negative charge and now it's an ion I'll cover that in a separate video. If you change the number of neutrons in this you now have an isotope of this element I'll cover that in a separate video and if you change the number of protons you now have a new element. You cannot change the number of protons the number of protons determines the atomic number of an atom which determines where it sits on the periodic table. So I'll cover that with a periodic table. All right so we are looking at what's called the planetary model. I usually call this the Bohr's model where you see the protons and neutrons in the nucleus and the electrons worrying around the outside but they don't follow this beautiful path. They're not like rings around the outside of a planet. They are whipping around the nucleus in a very erratic manner. We can only predict basically the vicinity that they're in not exactly where they are. So this isn't this is a great model a simplest model to draw but atoms look more like this. This would be the electron cloud model which means that the electrons in this elemental helium here this atom of helium are going to be worrying somewhere around the nucleus inside this cloud. Now the nucleus is going to have a positive charge because that's where your positive protons are. The electrons have a negative charge and just like a magnet right the opposites attract. So the positive nucleus is keeping these negative electrons from leaving from traveling too far away unless something pulls them away as we'll as we'll see with chemical reactions later. All right I think that's all the the basics that you need to know about the structure of an atom. We will talk about isotopes and the periodic table and all that and videos coming up. So I hope this helps. Have a wonderful day. Be blessed.