[Music] just as a cell is the basic structural component of biology the atom is the basic structural component of chemistry and you need to know the subatomic particles that make up the atom and how those pieces play into their properties and how we as scientists categorize them into diagrams we see like with the periodic table all matter that you can see feel and experience is made up of atoms and the cool thing is that no matter which atoms make up these components they are all built the same way just in different amounts the core of every atom can contain two components which are called protons and neutrons they sit at the center of the atom taking up a small very condensed space in the middle called the nucleus we can refer to both the protons and neutrons as nucleons because they will always be found within the nucleus protons are positively charged and neutrons do not carry a charge because the protons carry a positive charge the overall charge of the nucleus of every atom is positive the number of protons and neutrons that an atom has dictates its properties and mass let's first discuss this with a focus on the proton the proton is the single distinguishing factor for identifying which element the atom is on the periodic table because the number of protons informs us of the properties of the atom we call the number of protons the atomic number number when looking at a periodic table every element has their atomic number displayed above the chemical symbol so for example we can see that carbon has an atomic number of six which means it has a total of six protons in its nucleus calcium has an atomic number of 20 meaning we would find 20 protons in the atomic nucleus of every calcium atom this number unlike other subatomic particles cannot be changed and have the atom still retain its same properties if we have a carbon atom with six protons and one of those protons gets removed well we don't have a carbon atom anymore we now have a boron atom because boron has an atomic number of five the neutrons in the nucleus are a bit different neutrons as we stated before do not have a charge and they are not important for distinguishing the characteristic that defines the element so for that reason neutrons can be added or taken away from carbon and we can still classify it as carbon but while they do not impact the identity of the atom they do have an impact on the mass of the atom both protons and neutrons weigh nearly the same amount and without getting too technical we can say that they both have a mass of one atomic mass unit which we abbreviate as AMU I will put the actual values here for reference which you do not need to know and will be given to you in the data booklet and also give you a conversion so you can get a sense of just how small one AMU unit is so knowing that both protons and neutrons contribute to the mass of an atom if we were to add or remove neutrons neutrons it would therefore change the mass and if we were to add or remove protons it would change the mass and also change the element while the nucleons occupy the nucleus of the atom other subatomic particles called electrons occupy the space outside of and around the nucleus electrons carry a negative charge and the electrostatic force between the positively charged protons and the negatively charged electrons generate a force that keeps the electrons close by this complete occupied space of the protons neutrons and electrons defines a single atom just like neutrons electrons are not a defining characteristic of an atom so a carbon atom can lose an electron and it will still be carbon in addition electrons are extremely small which is saying a lot considering we are discussing atoms that are insanely small compared to anything else our senses experience on a daily basis but electrons are so small that we don't even count them when taking the mass of an atom their mass in AMU is around 00 05 which is so small that it does not really make a difference so for that reason we consider the mass of electrons to be negligible to the overall mass of an atom but electrons do carry a charge and they do contribute to the overall charge of an atom we will talk more about this in future videos but the idea is that if an atom gains or loses electrons they can either gain or lose negative charges which balance out with the positively charged protons in the nucleus and lead to many things like bonding all atoms are built on the same building blocks of protons neutrons and electrons and to notate the information of how many of these components are within a specific atom chemist use the nuclear symbol notation let's break down the pieces the large text in the middle is the chemical symbol of the element that is defined by one or more letters each element that we know of has its own chemical symbol carbon for example has a chemical symbol of C to the left of the symbol letter in the subscript position is the atomic number weall that the atomic number for an atom represents presents how many protons it has and this number is unique and tied to each element specifically carbon has six protons so its atomic number will be written here as six the superscript on the left side of the symbol represents the mass number of the element the mass number constitutes the mass of the atom which we said before only takes into account the protons and neutrons because the mass of electrons is negligible if carbon has six protons and six neutrons it would then have a mass number of 12 the last part the notation is a superscript to the right side of the chemical symbol which notes the charge of the atom but not every atom has a charge meaning that have an overall net charge of zero and in that case this part is left blank you can determine the overall charge of an atom by subtracting the number of electrons from the number of protons so in our example here with carbon we have six protons minus 6 electrons which would give us an overall charge of zero that we do not write but in a hypothetical situation if a carbon atom were to gain an electron we would do six protons minus 7 electrons which would give it an overall charge of minus1 this type of notation allows us to determine the values of some numbers if we know the others for example if we have a Cobalt atom that has a mass number of 59 AMU how many neutrons does it have take a second and pause the video to see if you can figure it out we know from the periodic table that Cobalt has an atomic number of 27 meaning it has 27 protons with a mass number of 59 we can subtract 27 protons from the total mass of 59 to get a total number of neutrons in the atom which is 32 be prepared to answer questions like this on the IB exam so what we have learned so far about atoms if you change the number of protons you change the element and the mass if you change the electron you change the charge and if you change the number of of neutrons you change only the mass so atoms of specific elements can have different masses based on how many neutrons they have in the nucleus which does not impact the element properties besides mass or the charge different versions of atoms of the same element that have different numbers of neutrons are called Isotopes this results in different atoms of the same element having a different mass number take carbon again as an example if this carbon atom has six protons and six neutrons it would have a relative mass number of 12 but if if another carbon atom had six protons and seven neutrons it would have a relative mass number of 13 these are two different isotopes of carbon and the proper notation to write these Isotopes out is using a hyphen followed by the mass number so this would be carbon 12 and this would be carbon 13 same protons same electrons different neutrons the reality is that many atoms have different isotopes that exist on our planet knowing this and putting together a diagram like the periodic table that has mass number information on it it which isotope should be used do we say that carbon has a mass of 12 or 13 on the periodic table because both Isotopes exist well the answer is we actually use all of the Isotopes of a particular element but we do it in a way that takes into account the relative abundance of each isotope found on the planet on Earth around 98.89% of carbon we find is carbon 12 with around 1.19% of the carbon being carbon 13 another unstable and Radioactive isotope of carbon exists which is carbon 14 but this takes up less than 0.00001% of all carbon atoms on the periodic table you will see the relative atomic mass of all isotopes with their Natural Abundance taken into account we calculate the relative atomic mass by multiplying each abundance percentage by their mass number adding those together and then dividing by 100 so for carbon we can take 12 * 98.89% we leave out the unstable and negligible Isotopes like carbon 14 and divide that by 100 to get a rounded answer of 12.011 and if we take a look at the periodic table that is what we have for the atomic mass of carbon you can also use this information to work backwards to find out what the relative abundance of each isotope is if you were to have the atomic mass but this only works when an element has two known stable isotopes take the element Boron which has two stable isotopes in boron 10 and Boron 11 given that the relative atomic mass of boron is 10.81 what are the abundance percentages of these two isotopes we can take the same equation and add in some unknowns to solve for so we know that the mass number of boron 10 multiplied by its abundance plus the mass number of boron 11 multiplied by its abundance and then divided 100 is equal to a mass of 10.81 we can replace our unknown for the abundance percentage of boron 10 with a variable X and because this represents a percentage of two numbers we can say that the abundance percentage of Boron 11 would be 100 minus the value of the abundance percentage of boron 10 which we said was X so we can substitute that with 100 - x we expand the bracket to get 10 x + 1,100 - 11x we resolve the X terms to get 1,00 - x we then solve for x by undoing the division with multiplication subtracting the 1,100 to move it to the other side and then resolving the negative to get a value of x = 19% which is one method to solve it so our relative abundance for Boron 10 is 19% leaving the relative abundance of boron 11 at 81% again you can expect to see questions like this on the IB [Music] exam [Music]