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group IA

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Grafter:
Thats right,

Li will form LiOH
Na will form NaOH
K will form KOH
Ca will form Ca(OH)2

Why do you think Ca forms a Ca2+ ion instead of a Ca+ ion?
How does NaOH act as a base in water? Can you write a dissociation equation?
What makes something a good base?

jdurg:
For everyone involved in this thread, great job!  You're doing a great job of leading the OP towards the answer Grafter, and rayan is picking up on the proper answers as she's going along.  This is what I like to see.   ;D

So rayan, take a look at the periodic table and compare the observations you have made to the location of those elements on the periodic table.  For the elements that have reacted the quickest, what common trait to they seem to have?  Remember that a chemical reaction involves the movement of electrons.  So if something doesn't want to get rid of its electrons, it's not going to react as quickly.  

Where is lithium on the periodic table?
How many electrons does lithium have?
How many electrons does it need to give up in order to have a full outer shell?  (By full outer shell, I mean how many electrons must it lose in order to have the same number of electrons as the noble gas that precedes it?  In this case it would be helium).  
That electron(s) that it needs to give up; how far away from the positively charged nucleus is it/are they?
So how tightly is the nucleus holding onto that electron(s) compared to say potassium or rubidium?
Since reactions involve the movement of electrons from one substance to another, why did you see that potassium and sodium reacted with water faster than lithium did?

With calcium, where is calcium on the periodic table?  (I.E. what column?)
Based on its position, how many electrons do you think it has to give up in order to have a full outer shell?
What do you think would be easier, removing one electron from something or removing two electrons?
Since chemical reactions involved the movement (transfer is probably a better word) of electrons, how do you think the group two metals would react with water in relation to the group 1 metals?  Would it be faster, slower, or the same?

Rayan:
hello..
Li belongs to group I, thus it has one valence electron and 7 other electrons to completet its octet, so it loses one electron. all the elements of this group tend to lose one electron too. but since as we go down a group, the number of shells increases, so this electron that will be lost will be more far away as we go down, so K loses its electrone easier than Na, which also loses its electon easier than Li.
Ca has to lose two electrons, and i suppose that it is harder than to lose one electron and that's why reactions of the elements of group II with water are slower than those of elements of group I with water  ;D
so?!?!

Grafter:
In calcium its not so much that its easier to loose 2 than it is to loose 1. The second ionisation energy will be greater than the first. Its more that the energy benefit from going 2+ instead of 1+ is more than enough to compensate for having to ionise twice.

GCT:

--- Quote ---hello.
i just want to know why do elements of group IA (H-Li-Na...) react vegorously with water.
thanks.
--- End quote ---

I guess the answer is related to effective nuclear charge, that is the strength of the nucleus in holding on to its electrons, IA elements have relatively lower proton numbers.

Grafter is right in saying, that the second ionization energy of magnesium would be disfavorable for the formation of the ionic compound, you'll need to consider the lattice energy (which also consists of neighboring anions and cations, such as those designated through a cubic cell).

You can also visualize the stability in terms of a PE diagram as a function of the internuclear spacing between the anion and cation.

edit: wrong trend in atomic radii

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