professor Dave here, let's name some ionic compounds as we just learned, sometimes atoms steal electrons from one another to become ions. there are many ionic substances, and we should be able to name them. but first, we must understand that ions come together to form compounds in ratios dictated by their charges. positively charged ions, or cations, will bind with negatively charged ions, or anions, to form neutral compounds by whatever combination necessary.
we can know the most common ion an element will form by looking at where it is on the periodic table. if an atom is in group 1 it needs to lose one electron to attain noble gas electron configuration, so 1 plus is what they tend to form. atoms from group 2 will tend to become 2 plus ions.
looking at the other side elements in the group called halogens need to gain one electron to attain noble gas electron configuration, so they will tend to become one minus ions. these will become two minus, these three minus, and so forth. to find out the ratio in which ions will bind, just put them together in a way that the positive and negative charges add up to zero.
sodium and chloride are one plus and one minus so one of each will do nicely. if we use magnesium instead of sodium magnesium is 2 plus, so each magnesium ion will need two chloride ions to make a neutral compound. if we have magnesium and nitrogen we will need three of the two plus and two of the three minus to get plus and minus six.
you just need the lowest common multiple for the two charges and use as many ions of each as you need to get there. when we write out ionic compounds we always list the cation first and then the anion. usually the cation is just referred to by the name of the element but the anion, if it's monoatomic, will have the suffix "-ide".
that makes this sodium chloride. some metals can have different common charges or oxidation states. copper can be 1 plus or 2 plus and we represent that with Roman numerals in parentheses. copper one means that it is a 1 plus ion and copper two means 2 plus.
if there is an element with two common oxidation states the lower one bears the suffix "-us". and the higher will be "-ic". so a copper ion is a cuprous ion and copper is a cupric ion.
for similar polyatomic anions with different numbers of oxygen atoms in them, the one with more bears the suffix "-ate". the one with less bears the suffix "-ite". so this is the nitrate ion and this is the nitrite ion.
if there are more still, we can use the prefixes per and hypo in addition to the suffixes. so this is chlorate. this is chlorite, this is hypochlorite, and this is perchlorate.
these prefixes and suffixes are used as necessary depending on how many variations a particular ion has. there's not very much memorization in chemistry if you understand what's happening, but unfortunately knowing the names and charges of these polyatomic ions is a case where you're just gonna have to memorize a little. these are the most important ones to know by name and their charge.
putting it together, if there's an ionic compound you want to name, just list the cation and anion by name, inserting prefixes and suffixes if necessary, like magnesium chloride. if the cation is a transition metal from the d-block, we need to refer to its oxidation state. here the sulfate is 2- so we know the chromium atom must be 2+, so this is chromium sulfate.
we can also go from a name to a formula unit if we have the name iron phosphate we know that we have iron atoms that are two plus and phosphates that are three minus so we will need three irons and two phosphates to make a neutral compound. the oxidation state of the iron atom is implied by the ratio in the formula unit but it is not implied in the written name that's why we specify with the roman numeral. if we are looking not at ions but at binary covalent compounds which contain only two elements we use a different set of prefixes to say how many atoms of each element there are. we can have carbon monoxide or carbon dioxide or something like tetraphosphorus trisulfide.
these prefixes are not necessary when there is only one possible combination between two elements so it's just magnesium chloride not magnesium dichloride. let's check comprehension Thank you. thanks for watching guys subscribe to my channel for more tutorials and as always feel free to email me professordavexplains at gmail.com