this is mr. W and this is a spoken lesson not a song about the chemistry that biology students need to know it's the first in a several part series you're studying biology but you need to understand chemistry because living systems are chemical systems just think of yourself a great example of a living system you take in food food is a chemical substance made it atoms combined into molecules that's chemistry when you've got just that food you take it you break it down into simpler forms some of which gets made into you that's chemistry you'll take other parts of that food you'll combine it with oxygen and you'll make it into molecules that your cells can use to do the work of life that's chemistry too it's all chemistry we're going to start our study of chemistry by looking at atoms atoms are the building blocks of matter they are unimaginably small the radius of a carbon atom one of the most important atom and living things is seventy trillions of a meter almost all the mass of an atom is found in a dense core called the nucleus the nucleus is made up of positively charged particles called protons and other particles called neutrons that have no charge at all orbiting outside of the nucleus way in the distance are negatively charged particles called electrons which have very little mass I've just used the term charge what does that mean what do you need to know you don't need to know very much charge is a fundamental property of certain particles particles like protons have a charged particles like electrons have a charged to and neutrons don't what you need to know as a biology student is that protons have a positive charge electrons have a negative charge that like charges repel and that unlike charges opposite charges attract in this representation of a carbon atom the atom itself is shown as a kind of miniature solar system the nucleus is about where the Sun would be and the electrons are shown kind of like planets orbiting outside the reality of atoms is much more complex and when you take chemistry you learn a much model but you don't need that for now the region where electrons are found has three dates they're called orbitals you can remember the word orbit they're called energy levels and we'll see that's because the amount of energy is corresponding to where they are and they're also simply called shells in an uncharged atom the number of protons and the number of electrons is equal the number of neutrons is usually about the same as the number of protons but it can vary we'll learn about what it means for an atom to have a charge later on in this course and we'll also learn about the importance of variations in the number of neutrons all the atoms that have the same number of protons are considered to be the same element and you've learned about many elements you've learned about oxygen you've learned about iron carbon uranium so on and so forth about 90 elements are found naturally on our planet about a dozen more have been cooked up artificially in laboratories around the world each element has its own one or two-letter chemical symbol and those are usually pretty easy to remember hydrogen symbol is H helium symbol as H II carbon symbol is see nitrogen symbol is n there are some atoms however that have chemical symbols that are not derived from English so for example sodium is na iron is Fe Gold is a you you'll learn this in the course of your studies of biology and chemistry the periodic table takes all of the elements and organizes them based on the number of protons and similarities of chemical properties each element has its own square and within that square you can find the atomic number the atomic number is the number of protons a chemical symbol which we just discussed the name of the element and the atomic weight which is exactly what it sounds like it's the weight of that atom which you get by adding up the protons the electrons and the average number of neutrons which is why it's often not a whole number the most important thing about the periodic table is how its organized here's what biology students need to know the number of protons of each element increases from left to right in each horizontal row for example find the second row in the periodic table which begins with Li for lithium lithium has three protons the next element beryllium with the symbol B e has four protons the next one boron is chemical symbol is B you have to jump across a gap to find it has 5 protons each vertical column represents a family of elements the elements in each family have similar chemical properties because the arrangement of their outermost electrons is similar something you learn about in the next few tutorials in other words lithium and the elements directly below it starting with Na for sodium are in the same family these are all metals that are very reactive which means that they're very quick to interact with other elements to understand biology you only need to be familiar with a small number of elements it's about a dozen and we'll meet them in the next video in this series what I want you to do now is go to my website and I want to implore you not to skip this step the reason why is that to learn you got to interact with the material and this might be a big disappointment but if your thinking is that watching a video is studying that's not exactly right you've got to make predictions you've got to answer questions and I've setup that for you at my website we applied flashcards on multiple choice quizzes and other learning activities so go right now to science music videos dot-com do the activities follow the links and then come back and meet me at the next video thanks you