Video instructions and help with filling out and completing How Form 8815 Representation

Instructions and Help about How Form 8815 Representation

Welcome to Lewis diagrams made easy with Ketz book today we're going to learn how to draw Lewis diagrams for atoms and simple molecules but before we begin let's start with the question how many valence electrons does chlorine have in order to answer that question we need to look at the periodic table remember that within any given column all the elements have the same number of valence electrons to get that number all we need to do is count the columns starting from the left skip the transition metals and remember that the only exception to this is helium which has only two valence electrons not eight now find chlorine in the periodic table remember that its symbol is CL C in the seventh column that tells us that it has seven valence electrons knowing the number of valence electrons an element has is critical and in Lewis diagrams we use dots to represent valence electrons so the Lewis diagram of chlorine is the symbol CL with seven dots around it when you draw the dots don't just put them anywhere instead imagine a square around the element symbol the dots should be neatly drawn on the four sides of the square with no more than two dots on any side practice drawing Lewis diagrams with a few elements just to make sure you've got it this is the Lewis diagram of hydrogen which has only one valence electron this is carbon which has four valence electrons and this is oxygen which has six valence electrons where you put the dots it doesn't really matter as long as you neatly draw them along the sides of an imaginary Square and never put more than two dots on one side Lewis diagrams are often used to represent covalent bonding in molecules and ions in covalent bonding atoms share valence electrons in order to get a full octet or do it that is every nonmetal element wants eight valence electrons except for hydrogen which only wants two valence electrons the simplest molecule possible is that of hydrogen h2 a hydrogen atom has one valence electron but it wants to have two so in order to satisfy its desire for another electron two hydrogen atoms will share their electrons with each other and the crazy thing is that in the wonderful world of atoms the shared electrons are counted as owned by both atoms that means that both hydrogen atoms are happy because they both satisfy the octet rule now we normally draw hydrogen and other molecules like this with lines to represent shared electrons and dots only for nonbonding electrons these two diagrams of a hydrogen molecule are equivalent because one line which is a single bond represents two shared electrons in the same way two lines between atoms would be a double bond and would be the sharing of four electrons an example of a molecule with a double bond is oxygen which looks like this notice that in this Lewis diagram both oxygen atoms have eight valence electrons four from the double bond and four from the lone pairs of electrons by the way two dots together are called a lone pair of electrons some molecules contain triple bonds which we write using three lines that represent the sharing of six electrons an example of a molecule with the triple bond is nitrogen which looks like this once again notice that both nitrogen atoms have eight valence electrons six from the triple bond and two from the lone pair of electrons okay how do you actually draw the Lewis diagram of a molecule let's start with water h2o there are five important steps that you need to follow when drawing the Lewis diagram of molecule first count all of the valence electrons in the molecule for water each hydrogen has one electron and we multiply that by two because there are two hydrogens in the molecule the oxygen has six valence electrons add those all up and we have a total of eight valence electrons for the water molecule step two determine the central atom the central atom is the one that all the other atoms will be bonded to it is usually the element that there is only one of in the case of h2o because there are two hydrogen's and only one oxygen we choose oxygen as the central atom and write it in the middle step 3 draw single bonds to the central atom step 4 put all of the remaining valence electrons on atoms as lone pairs for h2o we start with 8 valence electrons we have used 4 electrons for the two single bonds so that leaves 4 more electrons left over we put all four of these remaining electrons on oxygen instead of hydrogen because hydrogen is already happy with 2 valence electrons remember never give hydrogen more than 2 valence electrons everyone else wants 8 valence electrons but hydrogen only once 2 step 5 turn lone pairs into double or triple bonds to give every atom and octet or do it for hydrogen pause the video and see if all the atoms in our h2o are happy because each hydrogen has two electrons and the oxygen has eight electrons everyone is happy and there is no need for double or triple bonds which means that our Lewis diagram of water is now complete alright let's try one more example just to make sure that we've got this draw the Lewis diagram of sulphur trioxide once again the first step is to count all the valence electrons there is one sulphur with six valence electrons and there are three oxygens with six valence electrons each six times three gives us 18 valence electrons for the three oxygens the total would be 6 plus 18 which equals 24 valence electrons step 2 determine the central atom this time solvers the central atom because there is only one sulfur in the molecule we