hi guys in today's video we're going to take a look at what is an atom atomic structure subatomic particles mass number and atomic mass looking at an example of an element an exam style question and finally a summary so what is an atom well an atom is the fundamental piece of matter everything is made of atoms apart from energy so what i mean by that is that you're made from atoms the food you eat is made from atoms our galaxy is made from atoms our atom is the basic unit it's the smallest particle of a chemical element many models of the atom have been proposed over the years we have thompson's plum pudding model which shows a central positive sphere studded with negative electrons we have rutherford's model which proposed there was a central nucleus and we have bohr's model we'll take a closer look at a model similar to that proposed by boar so here we have that model we're going to look at the structure of the atom at the center of the atom we have our nucleus this is tiny and dense it's really intense because it contains almost all of the mass of our atom now our nucleus is composed of two things it's composed of our protons and are neutrons which are collectively known as nucleons as they are found in the nucleus orbiting our central nucleus we have electrons these orbit the nucleus in shells now they're really tiny and don't contribute much to the mass of our atom so let's take a closer look at these three subatomic particles are protons neutrons and electrons so as i mentioned there are three subatomic particles we're going to have a look at our protons and our neutrons which live if you like in the nucleus and our electrons which orbit that central nucleus we're going to look at the relative masses and the relative charges of our protons neutrons and electrons so first of all let's look at the relative charge our proton carries a positive charge i like to remember as p for positive our neutron carries a neutral charge n for neutral and our electrons carry a negative charge now if we take a look at the relative masses both our protons and our neutrons have a relative mass of 1.0 now we did mention that our electrons are tiny they have a relative mass of one over two thousand so you can see how small they really are now it's important to note that in neutral atoms the numbers of protons and electrons are equal and what that means is that the positive charge of the protons is equal to the negative charge of the electrons this allows for the atom to be overall neutral and carry no charge so it's not an ion so let's go ahead and have a look at how the number of protons neutrons and electrons are represented in a periodic table well the way this is done is through mass and atomic number you'll recognize this representation of an element with its mass anatomic number from your periodic tables and we're going to take a closer look at what each part of this representation means and is telling us so our x here stands for element this could be any element in the periodic table a is our mass number now this is the number of nucleons so that's protons and neutrons z is our atomic number this is just the number of protons so let's have a look at an example i've chosen the element aluminium here completely at random so let's take a closer look at aluminium and its mass and atomic number here we have aluminium with its mass number of 27 and its atomic number of 13. now as you can see this representation is slightly different to the general representation that we looked at some periodic tables would give the atomic number on the top and some on the bottom it's just important for you to recognize that the mass number which is the number of protons and neutrons will be the bigger number compared to the atomic number which is just the number of protons so here we can see we have our aluminium aluminium has a mass number of 27 so we know that the number of protons and neutrons is 27. its atomic number which is just the number of protons is 13. using these figures and our knowledge of subatomic particles we can calculate how many protons neutrons and electrons there are in an atom of our element aluminium so we know the number of protons is 13. we know our aluminium does not carry a charge it's neutral and therefore the number of protons will equal the number of electrons meaning there are also 13 electrons now we know the number of protons and neutrons is 27 and the number of protons alone is 13. so the difference between these two numbers will be the number of neutrons so 27 minus 13 gives us 14 neutrons so we have 13 protons 14 neutrons and 13 electrons question number one asks us how many electrons there are in an atom of the following element and we can see we have sodium we can see that we have a mass number of 23 and an atomic number of 11. so what does this tell us well we know that our mass number of 23 is the number of protons and neutrons in an atom of our element we know that our atomic number of 11 is equal to the number of protons so there are 11 protons we know that the number of protons equals the number of electrons therefore we will have 11 electrons and we can see that the answer will be b moving on to question two chromium has a mass number of 52. explain why vanadium comes before chromium on the periodic table well importantly we know that the order of the periodic table depends on the atomic number so if we go ahead and have a look at a periodic table we can see we have vanadium and chromium here we can see that vanadium has an atomic number of 23 and chromium an atomic number of 24 and this is why vanadium appears before chromium on the periodic table so let's go ahead and fill in the answer just as we've discussed so we've answered this question by explaining that the order of the periodic table depends on the atomic number vanadium has an atomic number of 23 and chromium of 24. this question is worth two marks the first comes from explaining that the order of the periodic table depends on the atomic number and the second for giving the atomic numbers of vanadium and chromium so let's move on to our third and final question for each of the following atoms complete the table to give the number of subatomic particles in each and you can see we have calcium and we have platinum so if we take a look at calcium to begin with we can see that we have a mass number of 40 and an atomic number of 20. now we know that our atomic number is the number of protons so we can go ahead and fill in that we have 20 protons we also know the number of protons is equal to the number of electrons so we also have 20 electrons now if we take a look at the bigger number our mass number now we know that the mass number is equal to the number of protons and neutrons so if we have a mass number of 40 and we know that we have 20 protons we can take that away to find out that we have 20 neutrons now if we look at platinum and do exactly the same thing our atomic number is 78 we know we have 78 protons and therefore 78 electrons our mass number is 195 so to work out the number of neutrons we have we can take away the number of protons that's minus 78 to give us 117 neutrons this question holds three marks one for the correct number of protons one for the correct number of neutrons in each and one for the correct number of electrons each and you can see if we break down the question going through methodically the atomic number number of protons and electrons and then looking at the mass number and how we can calculate the number of neutrons a question like this involving a few calculations is really quite straightforward hey guys i hope you're enjoying the video if you're looking for an amazing a-level chemistry resource join me today in my series of engaging bite size video tutorials just click the snap revise smiley face and together let's make a level chemistry a walk in the park