Polyatomic ions(questions)

[cheungcheung]

Would anyone help solve my questions?

1.Are all polyatomic ions have covalent bonds(the electrostatic forces between the shared electrons and bonded atoms)?

2.Are they covalent compound?

3.Like ammonium(NH4), how does it exist?

4.Why aren't they have 0 charged?

5.How to estimate the charge of them?

[budullewraagh]

Generally, polyatomic ions contain polar covalent bonds. Still, the difference between polar covalent and ionic bonding is really subject to opinion. The "rule" chemists use is that if the electronegativity difference of the bonded atoms is greater than or equal to 1.7, it's an ionic bond.

 

NH4+ is an actual compound because it forms three covalent bonds and a fourth bond called a coordinate covalent bond. This fourth bond is formed because the H provides both electrons required for the bond.

 

Polyatomic ions don't have 0 charges because they contain ions.

Ex:

Sulfate (SO4) with a -2 charge.

O

O=S=O

O

 

The sulfur can only make 6 bonds. The O2 each want to make 4 bonds, but cant, since sulfur cannot form 8 bonds. As a result, 2 oxygen atoms make double bonds and thus are happy, so to speak, while the other 2 oxygen atoms can only make 1 bond each. They are not happy. The SO4 -2 ion is unstable, as are all polyatomic ions. This is why you will never see a polyatomic ion alone unless suspended in an aqueous solution.

 

To estimate the charge, just figure out the amount of bonds the central atom (like N in NH4+ and S in SO4-2) can make and how many bonds the outside atoms would like to make. Then figure out the difference and there's your charge. Another example is the borate ion. Boron wants to make 3 bonds. There are 3 oxygen bonded to it, all of which want to make 2 bonds. The boron can bond with them all, but cannot form even one double bond (let alone 3) and still have all 3 oxygen atoms bonded to it. Consequentially, you end up with the following molecule:

O

O-B-O

 

Each O has a -1 charge since it only has 1 bond. There are 3 oxygen atoms. Therefore, borate is a -3 charged polyatomic ion.

 

 

I hope I answered all your questions well.

[cheungcheung]

Thank you. Your explanation helps me a lot.

However, I have still a question.

Would you like to answer me?

Is Covalent compound is compound?

Is ion a compound or element?

If ion is a not a compound, then why is polyatomic ion a covalent compound?

Cation combines with anion to form ionic compound,right?

Actually, maybe I don't have the clear concept about ionic compound and convalent compound?

 

 

I am actually a questional boy..

[admiral_ju00]

my chemistry is a bit laggy, but let me try.

 

1) Is Covalent compound is compound? Yes

2) Is ion a compound or element? Element

3) If ion is a not a compound, then why is polyatomic ion a covalent compound? Poly - more then 1 element, in this case it's is polar (charged) and share electrons

[BoyGenius1]

Hey, I know a lot about chem. so if you have anymore problems, you can see me too.

[Tesseract]

Thats right Boygenius is a chemist interested in nuclear science...

JK

[cheungcheung]

Generally' date=' polyatomic ions contain polar covalent bonds. Still, the difference between polar covalent and ionic bonding is really subject to opinion. The "rule" chemists use is that if the electronegativity difference of the bonded atoms is greater than or equal to 1.7, it's an ionic bond.

 

NH4+ is an actual compound because it forms three covalent bonds and a fourth bond called a coordinate covalent bond. This fourth bond is formed because the H provides both electrons required for the bond.

 

Polyatomic ions don't have 0 charges because they contain ions.

Ex:

Sulfate (SO4) with a -2 charge.

O

O=S=O

O

 

The sulfur can only make 6 bonds. The O2 each want to make 4 bonds, but cant, since sulfur cannot form 8 bonds. As a result, 2 oxygen atoms make double bonds and thus are happy, so to speak, while the other 2 oxygen atoms can only make 1 bond each. They are not happy. The SO4 -2 ion is unstable, as are all polyatomic ions. This is why you will never see a polyatomic ion alone unless suspended in an aqueous solution.

 

To estimate the charge, just figure out the amount of bonds the central atom (like N in NH4+ and S in SO4-2) can make and how many bonds the outside atoms would like to make. Then figure out the difference and there's your charge. Another example is the borate ion. Boron wants to make 3 bonds. There are 3 oxygen bonded to it, all of which want to make 2 bonds. The boron can bond with them all, but cannot form even one double bond (let alone 3) and still have all 3 oxygen atoms bonded to it. Consequentially, you end up with the following molecule:

O

O-B-O

 

Each O has a -1 charge since it only has 1 bond. There are 3 oxygen atoms. Therefore, borate is a -3 charged polyatomic ion.

 

 

I hope I answered all your questions well.[/quote']

 

 

1.How about nitrite(NO3-), why does the charge is like this but not 3-?

2.make 3 bond=to have 3 more electrons?

[admiral_ju00]

because it give 3 of it's ions to O

[budullewraagh]

you mentioned "nitrite" (NO2-) but actually said nitrate (NO3-).

 

in the nitrite ion, N takes a +3 charge, while each O takes a -2 charge. since there are 2 O trying to make 2 bonds each (in order to take the -2 charge), the N cannot give up enough e-. as a result, the one of the O atoms forms a coordinate covalent bond with the N and takes a negative charge.

 

the same thing works with the nitrate ion, except the N takes a +5 charge and collectively, the O wants to take a total of -6 worth of charges and can't. so, once again, one of the O takes a -1 charge and forms a coordinate covalent bond.

[cheungcheung]

you mentioned "nitrite" (NO2-) but actually said nitrate (NO3-).

 

in the nitrite ion' date=' N takes a +3 charge, while each O takes a -2 charge. since there are 2 O trying to make 2 bonds each (in order to take the -2 charge), the N cannot give up enough e-. as a result, the one of the O atoms forms a coordinate covalent bond with the N and takes a negative charge.

 

the same thing works with the nitrate ion, except the N takes a +5 charge and collectively, the O wants to take a total of -6 worth of charges and can't. so, once again, one of the O takes a -1 charge and forms a coordinate covalent bond.[/quote']

 

Sorry, I made a mistake. Actually, when I was writing it, I first thought nitrite

and wrote. Then I found it could be calculated, so I write the formula of that polyatomic ion nitrate ion.

By the way, would you tell me something I am still confused with?

How do you know that when nitrogen atom wants to gain 3 electrons and when to lose 5 electrons to become duplet state(the same electronic arrangement of helium atom) while it combines with other atoms?

I hope you would answer me. DEAR

[budullewraagh]

when it forms bonds, it is essentially gaining or losing electrons. when it bonds with metals, it "gains" e- (ex. Na3N). when it bonds with most nonmetals, it loses e- (ex. NO2).

[cheungcheung]

when it forms bonds, it is essentially gaining or losing electrons. when it bonds with metals, it "gains" e- (ex. Na3N). when it bonds with most nonmetals, it loses e- (ex. NO2).

 

But, does the bond of the NO3 is ionic bond?

And also, why in H2O molecule, it is bonded with covalent bond but not ionic bond, doesn't that hydrogen atoms lose electron for oxygen

because of the strong electrostatic force of attraction from the strong nucleus of oxygen.

What provided for the condition?

[budullewraagh]

no, it's not ionic; it's slightly polar covalent. in the H2O molecule, the H atoms don't "lose" the electrons, but the e- stray away from the H and towards the O, making it seem like there are O-2 and H+ ions.

[cheungcheung]

Generally, polyatomic ions contain polar covalent bonds. Still, the difference between polar covalent and ionic bonding is really subject to opinion. The "rule" chemists use is that if the electronegativity difference of the bonded atoms is greater than or equal to 1.7, it's an ionic bond.

 

1.7?? How about H2F? The electronegativity of hydrogen atom is 1.0 while the electronegativity of fluorine atom is 4.0, then why we still look it as a covalent compound?

[budullewraagh]

H2F? I've heard of HF, but H2F would require a coordinate covalent bond... But then the second H would have to provide both electrons, which it generally doesn't have. It's quite uncommon to see an H- ion. But yeah, it would be 1 coordinate covalent bond and one ionic bond. still, the ionic is also polar covalent to some extent.

[apathy]

my chemistry is a bit laggy' date=' but let me try.

 

1) Is Covalent compound is compound? Yes

2) Is ion a compound or element? Element

3) If ion is a not a compound, then why is polyatomic ion a covalent compound? Poly - more then 1 element, in this case it's is polar (charged) and share electrons[/quote']

 

 

 

well, a "..." compound would be a compound, wouldn't it?

 

and an ion is an ion, an element is an element. maybe you could call a monatomic ion an "element" but not really, since an element would be a pure neutral substance, the whole thing, a sample of it, if you will.

 

The word "compound" would refer to the whole thing, the neutral substance. So I wouldn't go calling an ion, polyatomic or not, a "compound" but really this is just semantics and the only people who would care are anal professors and maybe librarians.

[budullewraagh]

maybe you could call a monatomic ion an "element" but not really, since an element would be a pure neutral substance, the whole thing, a sample of it, if you will.

 

actually, an element is defined as a substance composed of atoms having an identical number of protons in each nucleus.

 

either way, it's quite irrelevant considering it's only the specifics of definitions. there is much more valuable knowledge to understand.