in this video we're going to focus on the atom its structure what it's made up of and things like that so let's begin let's focus on carbon if you look at the periodic table carbon has an atomic number of six it has six protons and six electrons the protons and the neutrons are found at the center or the nucleus of the atom surrounded in nucleus you have different energy levels in the first energy level carbon has two electrons that's the greatest number of electrons you can have in the first shell in the second shell or second energy level carbon has four electrons so as you can see the electrons are outside of the nucleus they're orbiting the nucleus electrons carry negative charges protons they have positive charges neutrons are neutral so carbon has a total of six electrons the two electrons on the inside are known as core electrons and the electrons in the last or the outermost energy level are known as the veence electrons so carbon has four veence electrons if you look where carbon is located on a periodic table it's found in group 4 A which is the same as group 14 elements in group 4 A typically have four veence electrons alkali metals which are found in group 1 A contain one veence electron alkali earth metals group 2 A contains two veence electrons the halogens which are in group 7 A contain seven veence electrons so you can find the number of veence electrons based on which group the element is located in consider the symbol H h stands for helium in the periodic table you're going to see something that looks like this there's a number on top and there's a number on the bottom and the smaller of these two numbers represents the atomic number and the larger of these two numbers is the average atomic mass which you can also use it as the mass number the number of protons is equal to the atomic number it's always like that so because helium has an atomic number of two it has two protons the number of neutrons is equal to the mass number minus the atomic number and the number of electrons is equal to the atomic number minus the charge so an atom which is electrically neutral which doesn't have a charge atoms have equal number of protons and electrons but ions they differ in their number of electrons and protons ions have unequal amounts of protons and electrons now an isotope of helium can be written this way sometimes you might see it like this the top number represents the mass number the mass number is usually the larger of the two the atomic number is the smaller one so if you see it this way just know that the mass number is on top but if it's written on a periodic table the top number is usually the atomic number whichever one is lower is the atomic number the higher one is the mass number so don't get confused about that helium which we said has two protons it also has two neutrons and as a neutral atom it has two electrons so if we draw the atomic structure of helium it has two protons which I'm going to represent it with a positive charge and two neutrons the neutrons are neutral but protons have a positive charge and surrounding the helium nucleus you have two electrons now opposite charges attract opposite charges they feel a force of attraction that pulls them together and like charges they repel so these two charges they feel a force that pushes them away from each other known as the electric force so now what about the two protons within the nucleus of an atom they feel an electric force that pulls them apart but yet they remain intact therefore there must be another force that keeps them intact the force that holds the nucleus together is known as the strong nuclear force and so that's why the protons they don't repel each other now a common question that you might see in chemistry is you need to be able to determine the number of protons neutrons and electrons inside an atom or an ion so let's say if you have the aluminum atom which has a mass of 27 and the atomic number of three and also the aluminum ion which has a charge of plus three go ahead and determine the number of protons neutrons and electrons in these two particles so the atomic number is the number of protons so both the atom and the ion has 13 protons the number of protons identifies the element now what about the number of neutrons the neutron number is the difference between the mass number and the atomic number so 27 - 13 is 14 so both the atom and the ion they have the same number of neutrons now what about the electrons the electrons is the atomic number minus the charge so this is going to be 13 minus 0 so therefore an aluminum atom has 13 electrons an aluminum ion is going to be 13 minus 3 which is 10 so the aluminum plus 3 cation contains 10 electrons positively charged ions are known as cations negatively charged ions are known as annions now if you add the 13 protons and the 13 electrons you get a net charge of zero so atoms are neutral but for the ion if you add the 13 protons with the 10 electrons which has a negative charge 13 + -10 is pos3 which is the net charge of the ion try these two phosphorus 31 and also the phosphide ion calculate the number of protons neutrons and electrons so the atomic number is 15 therefore both of these have 15 protons to find the neutron number it's going to be 31 - 15 which is 16 so both the atom and the ion has 16 neutrons but they're going to differ in the number of electrons the electron number we said was the atomic number minus the charge so 15 minus 0 is 15 so therefore the phosphorus atom contains 15 electrons now the phosphide ion is going to be 15 minusg -3 whenever you have two negative numbers or two negative signs next to each other the negatives they will cancel and turn into a positive number so it's really 15 + 3 therefore an ion with a negative charge has more electrons than protons so we have 15 protons which has a charge of 15 and 18 electrons which has a net charge of8 15 - 18 gives you a net charge of -3 so whenever you have a positively charged ion it tells you that that ion has more protons than electrons if you have a negatively charged ion that ion has more electrons than protons now let's focus on carbon what are isotopes let's consider the carbon 12 isotope and the carbon 13 isotope isotopes are composed of the same element so carbon 12 and carbon 13 these are isotopes of each other but chemically they behave the same way their chemical reactivity is exactly the same however their nuclear properties are different because the nucleus of carbon 13 is different than that of carbon 12 both of these atoms contain six protons and the number of protons or the atomic number identifies the element so any substance with six protons is going to behave as a carbon atom now the number of neutrons is a difference between the mass number and the atomic number so carbon 12 has six neutrons but carbon 13 has seven neutrons because 13 - 6 is seven now as an atom they both contain six electrons so now let's analyze carbon 12 and carbon 13 which are isotopes of each other so as you can see isotopes are composed of the same element in this case carbon now because they're made up of the same element they have the same atomic number in this case six and they also have the same number of protons so that's the similarities between isotopes isotopes differ in two things they differ in the mass number and in the number of neutrons so make sure you remember these facts so isotopes have the same number of protons same atomic number and it's composed of the same element isotopes differ in the neutron number and in the mass number now if we check out the symbol for carbon and if you look at the periodic table you'll see a six above it and below it 12.01 this number is not exactly 12 why is that why is it 12.01 and not 12 this number is really called the average atomic mass why is it called the average atomic mass and not simply the atomic mass keep in mind carbon has multiple isotopes the predominant isotope is carbon 12 but you also have carbon 13 and a very very tiny amount of carbon 14 but mostly carbon 12 and carbon 13 approximately 99% of carbon atoms in a sample is carbon 12 and the other 1% is carbon 13 the amount of carbon 14 is insignificant so we're not going to worry about it here so what this means is that if you have 100 carbon atoms 99 of those carbon atoms is going to be carbon 12 which means they have six protons six neutrons now out of those 100 atoms at least one out of those 100 carbon atoms is going to be carbon 13 where it has six protons seven neutrons it turns out that this mass number is an a weighted average of these two isotopes and the way to calculate a weighted average in this particular instance you need to multiply the mass by the respective percentage and add it up you got to find the sum so the average atomic mass is going to be the mass of carbon 12 times its percentage in the form of a decimal 99% is.99 as a decimal you simply take a 99 and divide it by 100 or you can move the decimal 2 units to the left so it's going to be 12 *.99 + 13 * 1% which is 01 12 *.99 is about 11.88 and 13 * 01 is3 when you add these two numbers you're going to get the average atomic mass of 12.01 so that's how you can calculate the average atomic mass of an element you have to take the weighted average of all the isotopes that are found in nature and make sure you multiply by their relative percent abundance try this example boron has two principal isotopes B10 and B11 approximately 80 81% is B11 and 19% is B10 using this information calculate the average atomic mass of an atom of boron so the average is going to be the mass of the B10 isotope which is 10 multiplied by the percentage as a decimal 19% is 19 and isotope B1 has a mass of 11 and a relative percent abundance of 81 as a decimal so 10 *.19 that's about 1.9 and 11 *81 that's uh 8.91 so if you add these two numbers you're going to get the average atomic mass of an atom of boron which is 10.81 now sometimes you may have to work this problem backwards sometimes you may want to calculate the relative percent abundance of each isotope consider chlorine chlorine has two main isotopes chlorine 35 and chlorine 37 if you look at the periodic table the average atomic mass of chlorine is 35.45 now knowing that do we have more of the CL35 isotope or the CL37 isotope which one is more predominant in nature because the average is closer to 35 than this 37 that tells us that chlorine 35 is more abundant in nature than chlorine 37 so how can we calculate the percentage for each now if you remember in the example of carbon 99% was carbon 12 1% was carbon 13 but these two numbers have to add up to 100 99% is 0.99 1% is 01 so let's say if 0.99 was x that means that 1 - x is 01 1 -.99 is 01 so to find the percentage you need to use x and 1 - x solving so let me illustrate let's say if we want to find the relative percent for CL35 it's going to be 35 * X for the other isotope it's simply 1 - X so we just got to solve for X so we have 35x here we're going to distribute the 37 37 * 1 is 37 and 37 *x is - 37x so at this point let's combine like terms 35x - 37x is -2x so what should we do next at this point we need to get x by itself so we got to move the 37 to the other side so let's subtract both sides by 37 so these two will cancel on the right side we have -2x on the left side 35.45 - 37 is -1.55 i'm not sure what just happened there so now let's divide both sides by -2 so 1.55 / -2 is equal to x so x is.775 keep in mind x was associated with cl35 775 is 77.5% keep in mind uh to go back from a decimal to a percent you need to multiply by 100 or move the decimal point 2 units to the right now 1us 775 is 225 which is 22.5% so that's the relative percent of chlorine 37 so if we have a thousand chlorine atoms in this sample how many of those atoms would be chlorine 35 and how many is chlorine 37 so out of a,000 atoms 7750 I mean 775 excuse me would represent chlorine 35 the other 225 would represent Cl37 so out of a thousand atoms 775 of those atoms is the chlorine 35 isotope the other 225 is the chlorine 37 isotope so that is it for this video that's all I got hopefully you found this video to be educational so thanks for watching and have a great day