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+ is what they
tend to form. atoms from group 2 will tend to become 2+. 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 1- anions
these will become 2- these 3- 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 1+ and 1- so one of each will
do nicely. if we use magnesium instead of sodium magnesium is 2+ 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 2+ and two of the 3- 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 monatomic
will have the suffix ide. that makes this sodium chloride. some metals can
have different common charges or oxidation states. copper can be 1+
or 2+ and we represent that with Roman numerals in parentheses
copper I means that it is a 1+ ion and copper II means 2+. if there is
an element with two common oxidation states the lower one bears the suffix ous
and the higher will be ic so a copper one ion is the cuprous ion and copper
two is a cupric ion. for similar polyatomic ions 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(II) sulfate. we can also go from
a name to a formula unit. if we have the name iron(II) phosphate we know that we
have iron atoms that are 2+ and phosphates that are 3-, 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
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