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Name: Caroline
Status: student
Grade: 9-12
Location: MI
Country: N/A
Date: October 2006

Question:
What kind of bond is sodium nitrate? I know that Na ( sodium) is a non-metal and that NO3(nitrate) is an ionic bond, so when they are together what is the name for that bond?



Replies:
Sodium actually is a metal, and it has a charge of positive one. Nitrate is a polyatomic ion, meaning atoms of oxygen and nitrogen are covalently bonded to each other (bonding due to the sharing of electrons), and the nitrate ion has a charge of (-1). If you look up nitrate on Wikipedia you can see a picture of the structure. When things that have full opposite charges on them bind due to the charge on each one, it is an ionic bond, so the bond formed between sodium (+1) and the nitrate ion (-1) is ionic.

Ethan Greenblatt
Stanford Department of Chemistry


Caroline,

Sodium is a metal (not a nonmetal), and it forms the +1 cation in most cases. In this situation it combines with the -1 charged nitrate ion, NO3-, to form NaNO3. This is an ionic substance and the bonds between sodium cations and nitrate anions are ionic bonds.

Best wishes, and keep asking questions


Caroline,

You can easily determine what any bond type is if you have access to a periodic table that contains the electronegativity of each atom. First, though, sodium IS a metal and NO3 contains three N-O covalent bonds. A bond is simply the term used when two atoms share electrons. If you subtract the electronegativity of each of the two bonding atoms the resulting number will tell you what type of bond you have. If the number is between 0 and 1.51, then you have a covalent bond (a relatively equal or completely equal sharing of electrons). If your number is greater than 1.51 then you have an ionic bond (unequal sharing of electrons). Remember that ionic bonds produce ions, meaning that the electrons involved in the bond reside on one atom the vast majority of the time, whereas electrons in a covalent bond spend closer to 50/50 time around each atom.

To determine what types of bonds NaNO3 contains, you first must draw out the complete structure. You can find the structure at www.chemfinder.com if you are unsure how to draw it. The structure contains two N-O single bonds, and N=O double bond and an Na-O bond. Electronegativities are as follows: N = 3.0, O = 3.5 and Na = 0.9. N-O bonds have an electronegativity difference of 3.5 - 3.0 = 0.5, which is less than 1.51 and means that the bond is covalent. O-Na bonds have an electronegativity difference of 3.5 - 0.9 = 2.6, which is higher than 1.51 and so is an ionic bond. Remember that ionic bonds produce ions, and in the structure you have a positively charged sodium and a negatively charged oxygen.

Matt Voss


Sodium nitrate is an ionic solid. However, in contrast to what you wrote, the bonding within nitrate is covalent, and sodium is a metal.

Richard Barrans
Department of Physics and Astronomy
University of Wyoming


Caroline,

First, sodium (Na) is considered a metal (not a non-metal). N and O are considered non-metals. But these are mostly irrelevant to the consideration of what bond occurs between Na and the nitrate ion. Notice that in NaNO3 we consider that the Na is a cation and the nitrate as an anion. This means that we expect Na to be (1+) and the nitrate ion to be (1-). As such, when the two come together they form a bond that is a result of of the electrostatic attraction coming from full charges - which is what an ionic bond is by definition.

Greg (Roberto Gregorius)


You have made an incorrect assumption (definition). Sodium (Na) is a metal and readily donates a single electron (a primary property of a metal) to form Na(+1). The bonds between the nitrogen and the oxygens is approximately covalent. The bonding between the Na(+1) and the (NO3(-1)) is essentially an ionic bond.

Vince Calder



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