now just like living organisms are made up of lots of tiny cells everything whether it's living non-living or even a cell itself is made up of lots of tiny particles which we call atoms in fact they're so tiny that a single cell probably contains more than 100 trillion of them and in today's video we're going to explore just what these atoms are and what they're made of the first thing to know is that each atom is made up of multiple smaller particles and its basic structure is a central nucleus surrounded by electrons which orbit around the nucleus in rings that we call shells although we've only shown one electron orbiting here in reality all of the electrons would be moving all the time the nucleus itself is made up of two different types of particles protons and neutrons which are packed together in a tight ball now the most important thing to remember here is the structure of the atom that we've just been through and also the relative mass and charge of each of the particles the protons and the neutrons have the same mass so we say that they both have a relative mass of one electrons meanwhile are comparatively tiny and have a mass 2,000 times smaller which is often written as just very small or sometimes even zero charge is a bit different though protons are positive and have a 1 plus charge and you can remember this as both proton and positive begin with a P neutrons have no charge so we say they're neutral and this is even easier to remember because the words neutron and neutral both start exactly the same way lastly electrons have a negative charge which is the same size as the positive charge of the proton so minus one it can be easy to get all of these mixed up but the best way to remember it is that we have positive protons and neutral neutrons and then we know that the electrons are the only one left so they must be the negative ones and remember that both of the particles in the nucleus have a relative mass of one but the electrons on the outside are much tinier the size of an atom depends on which element it is and we'll see what elements are in the next video but basically they are the different types of atoms in general we can say that atoms have a radius of around 0.1 nanome most of an atom is actually empty space because we measure from the nucleus all the way to the outer electrons orbit it's kind of like the solar system you have one big thing in the middle and lots of smaller things orbiting it but between these things is mostly empty space now although it looks pretty big in this picture the nucleus is actually really tiny if we compared its width to the width of the atom itself the nucleus is 10,000 times smaller although the electrons are actually even smaller and if we were to draw them to scale they'd be too small to see in this atom that we've drawn we have three protons in the nucleus and three electrons orbiting it because the number of protons and electrons is equal the positive and negative charges balance out and so overall the atom is neutral atoms can lose or gain electrons though in which case the charges would no longer balance and the overall atom would become charged when this happens we stop calling it an atom and instead call it an ion for example if we gave our atom an extra electron we'd still have three protons but four electrons and so the charges would no longer balance and it would now be a negative ion because there's more negative electrons than positive protons we'd call this a 1us negative ion because it only has one extra electron while if our ion had another extra electron it would then have two extra electrons overall and be a 2 minus negative ion on the other hand if an atom loses electrons then there'd be more positive protons than negative electrons so we'd get a positive ion and in this case we have three positive protons but only two negative electrons so our ion would have a 1 plus charge now we take a look at it in detail in another video but this here is the periodic table and each box in the table represents a different type of atom which we call an element so this box here represents the element oxygen and this one is the element lithium we call these boxes nuclear symbols and they tell us a whole bunch of information about the element to see exactly what they tell us let's take a look at the nuclear symbols of oxygen and lithium the first thing to notice is the elemental symbol which is the one or two letter symbol that represents that element so O represents oxygen and L I represents lithium then in the bottom left corner we have the atomic number which tells us how many protons the atoms of that element have so all oxygen atoms have eight protons and all lithium atoms have three protons and this is actually really important as it's the number of protons in an atom that determines which element that atom is lastly in the top left we have the mass number which tells us the total number of neutrons and protons in that atom so if we wanted to find out how many neutrons oxygen has we would do the mass number minus the atomic number which in this case would be 16 minus 8 so it has eight neutrons the number of neutrons an atom has isn't always the same as the number of protons though for example lithium has a mass number of seven so to find the number of neutrons lithium has we would do 7 minus 3 which equals 4 so lithium has four neutrons even though it only has three protons as we said at the beginning of the video the number of protons and electrons in an atom is always the same so the atomic number also tells us how many electrons the atom has which means oxygen would have eight electrons and lithium would have three if you haven't heard yet you can find all of our videos on our website cognito.org you'll also find questions flashcards exam style questions and pass papers and we track all of your progress so that you always know what to study next so sign up for free by clicking here or browse our playlist here 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