If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:7:41

Video transcript

so let's talk a little bit about groups of the periodic table now in a very simple way to think about groups is that they just are the columns of the periodic table and a standard convention is to number them this is the first column so that's Group one second column third group fourth fifth sixth seventh eighth nine 10 11 12 13 14 15 16 17 and 18 and I know some of you all might be thinking what about these F block elements over here if we were to properly do the periodic table we would shift all of these they're everything from the D block and P block all right words and make room for these F block elements but the convention is is that we don't number them but what's interesting why do we go through the trouble about calling one of these columns but calling these columns a group well this is what's interesting about the periodic table is that all of the elements in a column for the most part and there's tons of exceptions but for the most part the elements in the column have very very very similar properties and that's because the elements in a column or the elements in a group tend to have the same number of electrons in their outermost shell they tend to have the same number of valence electrons and valence electrons and electrons in the outermost shell they tend to coincide although there's a slightly different variation the valence electrons these are the react the electrons that are going to react while the which tend to be the outermost shell electrons but there are there are exceptions to that and actually there's actually a lot of interesting exceptions that happen in the transition metals in the d-block but we're not going to go into those details let's just think a little bit about some of the the groups that you will hear about and and why they react in very similar ways so if we go at Group 1 group 1 and hydrogen is a little bit of a of a strange character because hydrogen isn't trying to get to eight valence electrons hydrogen in that first shell just wants to get to two valence electrons like helium has and so hydrogen is is kind of it's it's not it's not it doesn't share as much in common with everything else in Group one as you might expect for say all of the things in in group 2 group 1 if you put hydrogen aside these are referred to as the alkali metals and hydrogen is not considered an alkali metal so these right over here are the alkali alkali metals now why do all of these have very similar reactions why do they have very similar properties well to think about that you have to think about their electron configurations so for example the electron configuration for lithium is going to be the same as the electron configuration of the of helium of helium and then you're going to go to your second shell 2s 1 it has 1 valence electron it has 1 electron in its outer in its outermost shell what about sodium well sodium is going to have the same electron configuration as neon and then it's going to go 3 s 1 so once again it has one valence electron one electron in its outermost shell so all of these elements in orange right over here they have one valence electron and they're trying to get to the octet rule this kind of stable nirvana for 4 atoms and so you could imagine is that they're very reactive and when they react they tend to lose this electron in their outermost shell and that is the case these alkali metals are very very reactive and actually they have very similar properties they're shiny and soft and actually they're because they're so reactive it's hard to find them where they haven't reacted with other things well let's keep looking at the other groups well if we move one over to the right this group to right over here these are called the alkaline earth metals alkaline alkaline earth metals and once again they have very similar they have very similar properties and that's because they have two valence electrons two electrons in their outermost shell and also for them not as quite as reactive as the alkali metals but let me write this alkaline earth metals but for them it's easier to lose two electrons than to try to gain six to get to eight and so these tend to also be reasonably reactive and they react by losing those two outer electrons now something hat interesting happens as you go to the d-block and we studied this when we looked at electron configurations but if you look at the electron configuration for say scandium right over here the electron let me do it in magenta the electron configuration for scandium so scandium scan diems electron configuration is going to be the same as argon it's going to be argon the Aufbau principle would tell us that the electron configuration we would have the 4s - just like calcium but by the Aufbau principle we would also have one electron in 3d so it would be argon then 3d one for s2 and to get things in the right order for our shells let me put the 3d one before the 4s - and so when people think about the Aufbau principle they imagine all of these d-block elements as somehow filling the d-block now as we know in other videos that's not exactly true but when you're conceptualizing the electron configuration it might be useful then you come over here and you start filling the p-block so for example if you look at the electron configuration for let's say carbon carbon is going to have the same electron configuration as helium as helium and then you're going to fill your s block to s 2 and then to p1 - so - p2 so how many valence electrons does it have well in its second shell its outermost shell has two plus two and has four valence electrons and that's going to be true for the things in this group and because of that carbon has similar bonding behavior to silicon - the other things in its group and we can keep going on you know for example oxygen and oxygen and sulfur these would both want to take two electrons from someone else because they have six valence electrons they want to get to eight so they have similar bonding behavior you go to this yellow group right over here these are the halogens so there's a special name for them these are the halogens and these are highly reactive because they have seven valence electrons they would love nothing more than to get one more valence electron so they love to react in fact they especially love to react with the alkali metals over here and then finally you get to kind of your atomic Nirvana in the noble gases here and so the noble gas is that's the other name for the group 18 elements noble gases and they all have the very similar property of not being reactive why don't they react they have filled or their outermost shell they don't find the need they're noble they're kind of above the fray they don't they they don't find the need to have to react with anyone else
Biology is brought to you with support from the Amgen Foundation