Ionic bonding?

[blackettstreet]

This is sort of urgent so if nothing happens in about 10 minutes it doesn't matter. I am completely stuck over this ionic bonding, I need to know what happens when:

1. two atoms, each with one electron in their outer shell (not hydrogen!), bond - where do the electrons end up?

2. an atom with two electrons in its outer shell and one with 7 bond. does one atom end up with one electron in its outer shell?

Any help much, much appreciated because I have not got a clue

 

[Yew]

Right, atoms want an outer shell full of electrons, so Lets say we have NA (with one outer shell electron) and Cl (with seven)

The Electron from the NA will be 'taken' by the chlorine, Hence the NA will have an outer shell of 0 electrons, and the CL will have 8

Because electrons are negatively charged, the Na is now positively charged, and the Cl is negatively charged. Now in magnets, opposite charges attract, this is the same for these charges. Because two positives will not stick together, a lattice structure forms. (think a bit like bust-a-move, different colours stick, some colours disappear ie; bounce away)

 

[blackettstreet]

Right, atoms want an outer shell full of electrons, so Lets say we have NA (with one outer shell electron) and Cl (with seven)

The Electron from the NA will be 'given' to the chlorine, Hence the NA will have an outer shell of 0 electrons, and the CL will have 8

Because electrons are negatively charged, the Na is now positively charged, and the Cl is negatively charged. Now in magnets, opposite charges attract, this is the same for these charges. Because two positives will not stick together, a lattice structure forms. (think a bit like bust-a-move, different colours stick, some colours disappear ie; bounce away)

I know how the atoms want to fill their outer shells, but what about when they can't both get full outer shells?

 

[ralphchadkirk]

Ionic bonds are formed through an electrostatic attraction. What does that mean I hear you ask? Well, it's simple when you break it down. +'s are attracted to -'s and vice versa. Now, atoms always want a complete outer shell, and they'll do anything to achieve this. This is because a complete outer shell is very stable.

So, let's look at Sodium and Fluorine. Sodium has 1 electron in the outer shell, so it needs to lose one in order to have a complete shell (which will be the next one down). Fluorine has 7 electrons in its outer shell, and 8 would make it a complete shell.
So Sodium is nice and gives an electron to Fluorine. Now both have a complete outer shell.

Now, because an electron is negatively charged, by giving one away the Sodium atom is now positively charged, and by gaining one the Fluorine is now negatively charged. So they stick together because of the electrostatic force.
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What elements are these?

 

[blackettstreet]

Ionic bonds are formed through an electrostatic attraction. What does that mean I hear you ask? Well, it's simple when you break it down. +'s are attracted to -'s and vice versa. Now, atoms always want a complete outer shell, and they'll do anything to achieve this. This is because a complete outer shell is very stable.

So, let's look at Sodium and Fluorine. Sodium has 1 electron in the outer shell, so it needs to lose one in order to have a complete shell (which will be the next one down). Fluorine has 7 electrons in its outer shell, and 8 would make it a complete shell.
So Sodium is nice and gives an electron to Fluorine. Now both have a complete outer shell.

Now, because an electron is negatively charged, by giving one away the Sodium atom is now positively charged, and by gaining one the Fluorine is now negatively charged. So they stick together because of the electrostatic force.

But i mean, i've done ones where it adds up nicely to full outer shells. But i have here, for example, Magnesium (2 in its outer shell) and Chlorine (7 in its outer shell). I don't know how that can work?

 

[ralphchadkirk]

But i mean, i've done ones where it adds up nicely to full outer shells. But i have here, for example, Magnesium (2 in its outer shell) and Chlorine (7 in its outer shell). I don't know how that can work?

Mg has a +2 charge, and Cl has a -1 charge. So, to equalise the charges it has to be MgCl2.

 

[SS4]

I know how the atoms want to fill their outer shells, but what about when they can't both get full outer shells?

If we assume that A donates an electron to B

There is a ratio formed in which electrons are donated according to how many they have. In the case of potassium oxide (K2O) each potassium atom donates an electron to the oxygen atom. This ratio will always be kept

If there is excess of A then it will react with whatever of B is available in the correct ratio and then the rest of A won't react assuming that the surroundings are inert. In this case we call B the limiting reagent.

 

[blackettstreet]

Mg has a +2 charge, and Cl has a -1 charge. So, to equalise the charges it has to be MgCl2.

But how does that affect where the electrons go?
Sorry, i must sound really stupid i have this thing in front of me where i have to draw circles to reprsent the shells, and then mark where the electrons are on them... I haven't done this in any detail yet

 

[SS4]

But i mean, i've done ones where it adds up nicely to full outer shells. But i have here, for example, Magnesium (2 in its outer shell) and Chlorine (7 in its outer shell). I don't know how that can work?

Magnesium will donate an electron to two different chlorine atoms forming MgCl2.

IMO the easiest way to think about it is that the sum of charges in the compound must be zero.

 

[ralphchadkirk]

But how does that affect where the electrons go?
Sorry, i must sound really stupid i have this thing in front of me where i have to draw circles to reprsent the shells, and then mark where the electrons are on them... I haven't done this in any detail yet

Because the Magnesium will give its 2 electrons with 2 different Cl atoms.

 

[blackettstreet]

Magnesium will donate an electron to two different chlorine atoms forming MgCl2.

Ah! that makes sense! Starting to get it now!

 

[SS4]

But how does that affect where the electrons go?
Sorry, i must sound really stupid i have this thing in front of me where i have to draw circles to reprsent the shells, and then mark where the electrons are on them... I haven't done this in any detail yet

I assume you have a dot-cross diagram

Take the two outer electrons from Mg (represented by crosses) and put one cross into each chlorine atom.
In case a picture helps: http://www.gcsescience.com/a9-reaction-magnesium-chlorine.htm

 

[Royston Vasey]

But i mean, i've done ones where it adds up nicely to full outer shells. But i have here, for example, Magnesium (2 in its outer shell) and Chlorine (7 in its outer shell). I don't know how that can work?

If your example is Mg and Cl, then two Cl- ions will bond per Mg2+. I'm not quite sure what the question is really asking. Nominally, were the atoms/ions in isolation you would produce an MgCl moiety but this would be very unstable. The one free electron would we extremely labile and easily lost to another Cl.

 

[blackettstreet]

right....i have that one sorted, thanks for the help

what about potassium and bromine? they both have 1 electron in their outer shell?

 

[Clint]

And for god's sake don't read anything about wave-particle duality until you've finished your exams!

 

[blackettstreet]

I'm not quite sure what the question is really asking.

Well, it's a dot-cross diagram thing.....not really done negatives and positives yet.
I'm sort of getting this a bit more now although I'm pretty annoyed that i got this in the first place when i haven't studided it yet!

Anyway, could anyone tell me what happens when both atoms have one electron in their outer shell?

 

[SS4]

right....i have that one sorted, thanks for the help

what about potassium and bromine? they both have 1 electron in their outer shell?

Potassium donates an electron to Bromine (same as the Sodium/Chlorine example).

This is one of the joys of chemistry, there are a number of periodic trends which, as soon as you know one, you know them all

 

[ralphchadkirk]

right....i have that one sorted, thanks for the help

what about potassium and bromine? they both have 1 electron in their outer shell?

Well, I'm not just going to give you the answers. Given what we've covered, what do you think it would be?

Edit - Oh well, SS4 has given you the answer! It's KBr.

 

[blackettstreet]

Potassium donates an electron to Bromine (same as the Sodium/Chlorine example)

That's what I guessed at... so bromine ends up with two in its outer shell?

 

[SS4]

That's what I guessed at... so bromine ends up with two in its outer shell?

Nope. Bromine has 7 electrons in it's outer shell and then it gains one.

 

[blackettstreet]

Nope. Bromine has 7 electrons in it's outer shell and then it gains one.

oh gosh i've counted wrong that one's a lot simpler now!

i get it a bit more now. thanks everyone for the help

 

[ralphchadkirk]

Do you know how many electrons should be in each shell blackettstreet? This is vital knowledge.

 

[SS4]

You can find out how many electrons are in the outer shell by looking at their group (column) in the periodic table (excluding the transition metals)

 

[blackettstreet]

Do you know how many electrons should be in each shell blackettstreet? This is vital knowledge.

yh, 2 in the first then 8 in each of the next. but i just miscounted in 8's in the bromine my bad, sorry
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You can find out how many electrons are in the outer shell by looking at their group (column) in the periodic table (excluding the transition metals)

yes, i should have done that!

 

[YorkshireBear]

AS or GCSE Chemistry we doing here?

Dont worry youll get it So easy once you know it i promise!

 

[blackettstreet]

AS or GCSE Chemistry we doing here?

Dont worry youll get it So easy once you know it i promise!

GCSE, just started yr9. i've only had about three hours of this....

can i say to all, please don't judge my intelligence on this i normally am more switched on, promise!

 

[ralphchadkirk]

I suspect GCSE. An AS candidate would be expected to already have a good grasp of ionic bonding in common elements, and the patterns in the periodic table.

 

[Royston Vasey]

Ugh, dot-cross disgrams! Such a misrepresentation of the quantum beauty of orbitals!

The full outer shell thing is a way of describing the stabilisation of electrons by their occupation of lower energy levels in a molecule or ionic lattice. The shells thing actually relate to electrons at differing energy levels in different shape orbitals, and the likelihood of finding an electron at that distance and orientation from the nucleus. Electrons are best described as waves rather than particles anyway, and actually it is legitimate to describe the negative charge as being distributed in a non-uniform field. The "position of the elctron" is really best described as "the region of highest concentration of negative charge".

In this case of Mg and Cl, forming an ionic compound, the lowest energy (therefore favoured) state is where the highest energy electrons of Mg are transferred into the unfavoured "almost full" energy levels (orbitals) of Cl.

That is degree level Chemistry really though!

 

[ralphchadkirk]

The full outer shell thing is a way of describing the stabilisation of electrons by their occupation of lower energy levels in a molecule or ionic lattice. The shells thing actually relate to electrons at differing energy levels in different shape orbitals, and the likelihood of finding an electron at that distance and orientation from the nucleus.

I'm aware of that (that's AS Chemistry!) but I didn't want to over-confuse blackettstreet.

 

[Royston Vasey]

Anyway, could anyone tell me what happens when both atoms have one electron in their outer shell?

Well, a number of things could happen, but the likelihood is you'll form a solid of oxidation state zero where the electrons are spread between the many nuclei within the solid. The free electrons will be very reactive. See the reaction of Na (s) with water, forming NaOH (happy ionic compound) and H2 (stable covalent compound).

Both atoms being one away from a full shell will form a covalent bond, eg Cl2.

When hydrogen is one of them, e.g. HCl there is a bond which has both ionic and covalent character!
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I'm aware of that (that's AS Chemistry!) but I didn't want to over-confuse blackettstreet.

Sorry, I get very enthusiastic about chemistry!