[Music] hi and welcome back to free science lessons by the end of this video you should be able to draw dot and cross diagrams for the formation of ionic compounds okay i'm showing you here the ionic compound sodium chloride and magnesium oxide in this video we're going to look at how ionic compounds such as these form as we've seen sodium chloride is an ionic compound remember that sodium is a metal and chlorine is a non-metal i'm showing you here the electrons in the outer shells of an atom of sodium and an atom of chlorine i'm using dots and crosses but you need to understand that they both show electrons i'm also showing you the electron configuration of these two atoms in both cases the number of protons in the nucleus is the same as the number of electrons so that means that both of these atoms are neutral now the key factor you need to learn is that many atoms react in order to achieve the electron configuration of a noble gas i'm showing you the electron configurations of the noble gases neon and argon as you can see sodium can achieve the same electron configuration as neon by losing one electron and chlorine can achieve the same electron configuration as argon by gaining one electron now one really important idea you need to understand is that in ionic bonding electrons are transferred from the metal to the non-metal so in this case the electron in the outer shell of the sodium atom is transferred to the outer shell of the chlorine atom because the sodium atom has lost an electron it now forms this sodium ion which has a charge of positive one the chlorine atom has gained an electron so it forms the chloride ion with a charge of negative one now there are a couple of points that you need to understand firstly both ions now have the same electron configuration as a noble gas this sodium ion has the same electron configuration as neon and the chloride ion has the same electron configuration as argon secondly the square brackets tell us that the charge is spread over the whole ion these positive and negative ions are now attracted to each other by electrostatic forces of attraction okay i'm showing here the electronic structures of magnesium and of oxygen i'd like you to complete the dot cross diagrams for the ions formed when these react i'd also like you to work out the electron configuration of the ions and state which noble gas has the same electron configuration so pause the video now and try this yourself okay in this case the 202 electrons from the magnesium atom will be transferred to the oxygen atom i'm showing you the dot and cross diagrams of the ions here and as you can see both ions have the same electron configuration as the noble gas neon in the next video we're going to look at how ions form a giant ionic lattice and we're going to use this to explain the physical properties of ionic compounds [Music] you