so let's learn about chapter five today so chapter five talks about atoms molecules and subatomic particles so what is an atom so make sure you know and remember the definition of the word atom an atom is the smallest particle of an element that can exist and still have properties of that element and now remember the definition of an element something that cannot be broken down chemically now atomic theory of matter this is also called as dalton's atomic theory this is the other word for it dalton's atomic so this says that matter is made up of small particles called atoms and there are 118 types of atoms so all matter is made of atoms atoms of the same element are similar and the number of atoms that are arranged the type of combination you have determines the identity of a pure substance example water the formula for water is h2o that means two hydrogen atoms and one oxygen atom is together making the molecule of water now these atoms can rearrange or separate or unite to form new substances which you'll see when we do chemical reactions atoms can participate in an in or result in a chemical change but atoms cannot be destructed so you need to know these for multiple choice questions for the dalton's atomic theory none atom is really small so if you look at that that little dot there the diameter of an atom is 0.15 to 0.1 to 0.5 nanometers remember nanometers is 10 to the power of negative 9. this is 1 2 5 10 billionths of a meter so if the diameter of that dot was one millimeter then you can have 10 million hydrogen atoms form a line across that dot so that tells you an atom is really small what is the definition of the word molecule a group of two or more atoms that is strongly bound to each other so when you have two or more than two atoms that are strongly bound to each other we say it's a molecule an example of that could be o two this is a molecule you have two oxygen atoms that are strongly bound to each other now let's talk about the words in molecules diatomic what does the word die mean die stands for two so when it contains two atoms it's diatomic you need to learn this list these are seven die atomic these are seven diatomic gases in nature hydrogen nitrogen oxygen chlorine chlorine bromine and iodine and you can learn this like this learn the statement horses need oats for clear brown eyes so this will remind you of hydrogen nitrogen oxygen fluorine chlorine bromine and by eyes i mean nothing but iodine okay now what do you mean by triatomic triatomic the word try to remind you of three atoms so triatomic is three atoms example o3 that's ozone polyatomic what does the word poly mean poly means many so when you have many atoms together in a molecule like b4 s8 plus phosphorus and sulfur what do you mean by the word homoatomic homoatomic means all atoms are the same kind so all the ones that you just did now are all homo atomic like in hydrogen molecule both are hydrogen in ozone molecule o3 all are oxygen what's heteroatomic molecule hydroatomic would be when you have two or more different kinds of atoms present an example of a heteroatomic molecule would be water where you have two hydrogens and one oxygen okay so these definitions are important to remember for multiple choice so this is an example of the elements we were talking the molecules we were talking about earlier so if you look at chlorine i'm gonna say chlorine is diatomic because there are two atoms four in phosphorus so i'm going to say it's polyatomic similarly we are going to say sulfur is also polyatomic and all of these are homo atomic elements because they are made up of the same atom now these ones here all of these are heteroatomic why because when you look at them they are not made up of the same atom you can see they are made up of different atoms a and b the first one is diatomic because you have two atoms the next one aba is tri it has three the next one is tetra tetra also stands for four and the last one is also tetra so when we have four atoms together we can also call that as polyatomic or tetraatomic now let's learn about molecular compounds compounds that have heteroatomic molecule that means they have different atoms as a structural unit example sugar table sugar that is sucrose now what is the formula for table sugar so the table sugar formula is c12 h22 oh that means sucrose has 12 carbon atoms 22 hydrogen atoms and 11 oxygen atoms okay this is a molecular compound a molecular compound is made up of only non-metals and if you remember on top hat the other day i showed you a step up ladder and anything on the right of the step-up ladder was a non-metal molecule is a limit of physical subdivision and atom is a limit of a chemical sub division now let's talk about two kinds of atoms are present but one kind of molecule molecules have different properties than that of an atom so if you know water is a molecule it has different properties compared to what the hydrogen atom has and what the oxygen atom has it's made up of these but they all have different properties now what is an ionic compound an ionic compound example is sodium chloride ionic compound is a combination of a metal and a non-metal there are more combinations possible and we will discuss them in chapter seven but for now know that sodium is a metal chlorine is a nonmetal this is an ionic compound now the difference in the molecular and an ionic compound in a molecular compound for example ch4 you can see there's one molecular unit whereas in an ionic compound like nacl you can see there's one formula unit n a plus c l minus that is repeated over and over again in a regular repeated pattern now describing pure substances so pure substance can be broken down as compound or element element is made up of only one kind of atom whereas compounds made up of two or more types of atoms in an element you could have an individual atom example silver copper iron these all the symbols i'm writing homoatomic could be your seven diatomic gases right that's oxygen fluorine and chlorine i've written under compound you could have heteroatomic they could be different and their molecules or ions like example we solve an ionic compound was nacl and a heteroatomic molecule which is made up of two non-metals could be water that's h2 oh so this here again just gives you examples of elements while hydrogen and oxygen compounds water and hydrogen peroxide a mixture is a physical mixture of two harmonic elements or a mixture of even compounds is possible now natural and synthetic compounds these compounds could be naturally or artificially made now let's learn how to read chemical formulas so chemical formulas are made up of symbols the subscripts that are the numbers written lower indicate the number of atoms so if you look at h2o you see a subscript 2 here right that is written lower so h2o is water what is water made up of i'm going to say two atoms of hydrogen and one atom of oxygen are present in one molecule of water so this is how you read this formula okay so let's you try and read the next one pause the video and try and read it this is glucose so if you read this as six atoms of carbon 12 atoms of hydrogen and six atoms of oxygen are present in one molecule of glucose then you read this correctly both of these are molecular compounds because hydrogen oxygen carbon they all are non-metals now let's talk about subatomic particles okay so the subatomic particles will be covered in a different lecture video