Why does reactivity increase as you go down a group (column) for alkali metals (H, Li, Na, K, etc.) and decrease as you go down a group for halogens (F, Cl, etc.)

Something to do with outer shells?

 

Thanks in advance.

because of electronegativty and electron affinity due to the structural make up of the atoms with F being the most electronegative of them all and all increase in the electronegative value the closer they get to F

a simple tip for you.

get a periodic table, and in the botom left hand corner put a (+) sign and in the top right hand corner put a (-) sign.

make an imaginary line between the 2.

after a while you`ll begin to get a "feel" where certain elements sit and how they`ll react with others that fall along this line as it travels across the groups and the periods.

 

there is other data on this forum that explains this exact thing, read up on them too, but trust me about the + and - in each corner, it`ll help eventualy

YT2095 said in post # :

a simple tip for you.

get a periodic table, and in the botom left hand corner put a (+) sign and in the top right hand corner put a (-) sign.

make an imaginary line between the 2.

after a while you`ll begin to get a "feel" where certain elements sit and how they`ll react with others that fall along this line as it travels across the groups and the periods.

 

there is other data on this forum that explains this exact thing, read up on them too, but trust me about the + and - in each corner, it`ll help eventualy

 

That's not an explanation of the phenomenon, it's a statement that it exists.

 

 

Basically, the most stable form of an atom (ion) is one in which all the electron shells are either entirely full or entirely empty; this is why Nobel Gasses are so unreactive.

 

All reactions are an elements 'attempt' (there's no motive involved, it's just to do with energy levels; it's like a ball falling off a shelf; the most stable form is the one with the least energy, and it's always trying to give the excess energy off [by reacting, or falling off the shelf, respectively]) to get full (or at least, more stable) electron configurations.

 

To use the example of groups VII and I that you gave (halides, earth metals), the simplest way they can get similar to the structure of a nobel gas is to gain an electron (if you're a halide) or lose an electron (if you're a group 1 metal); this is pretty obvious from looking at the periodic table.

 

The more electron/proton pairs the atom has, the less force is acting on the outer electrons, because of an effect called 'Shielding'. Basically, the inner electrons are 'getting in the way' of the positive electric field coming out of the nucleus, so the more shells there are, the less the outer ones are attracted.

 

Now think about what would be most accepting to a new electron; it's obviously going to be the smallest atoms, because they have much less shielding, and attract more.

 

If you think about giving electrons away, the easiest way to do it will be with a large atom, where there are lots of inner shielding electrons.

 

Now lets combine that with the bonding pattern above.

 

The halides want to TAKE an electron, and it gets easier to take an electron the smaller the atom is, and harder the larger it is (because of the increased shielding the larger the atom is, remember). Hence, the most reactive halides are at the TOP of the group, and the least reactive are at the BOTTOM.

 

If we look at the group 1 metals, they want to GIVE an electron. It's easiest to give an electron when you're a big atom, and there's more shielding. Hence, the most reactive group one metals are at the BOTTOM, and the least reactive are at the TOP.

didnt know anybody said nobel gases anymore i was cut greatly at school by my chem teacher for saying nobel instead of inert.......

Crash said in post # :

didnt know anybody said nobel gases anymore i was cut greatly at school by my chem teacher for saying nobel instead of inert.......

 

I do. So did my chemistry supervisor, and many other people.

 

Anyway, they're NOT inert, so it's a pretty stupid forced rename.

i thought they were the closest you could get to inert, even if you can make the occasional compounds with them

They are.

and I still call them nobel gasses (not many chem teachers will argue with me face to face). and as mrl pointed out, it was dumb name change! at least Nobel gasses was more Non-commital

 

edit: if ya get stuck tho, just call em Group 8 chems, no-one can argue with that

 

i guess i will stop my reform of lingo and resume nobel gases

thanks MrL_JaKiri, explained it well

Hello everyone.

 

Might I correct thee a wee bitty?

 

That would be Noble, not Nobel. As they were so reluctant to react, they were considered more noble than other gases.

 

Nothing to do with mr. Nobel or the prize.

 

Just nitpicking here, but it seems to me to be in order, especially in these forums.

 

Eg. iron oxide? Ferric or ferrous?

it depends on which oxide it is. Fe2O3 and Fe3O4 are ferric. the former could be specified by adding "red" somewhere in its name and the latter oculd be specified by adding "black" somewhere in its name. FeO is ferrous oxide.

oh, and btw, please never, ever mistake reactivity for activity