2sodium + iodine ---> 2NaI

Hi , i am studying a chemistry example and i read this :

2sodium + iodine ---> 2NaI

i understand the chemical addition here. But why do i need the ( 2) on both sides of equations ?

the electrical charge of Na = 1 and so is Iodine's.

I have several examples like that and i cant figure out how do they come up with these charges .
any ideas ?
c_hocklandAsked:
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dragonjimConnect With a Mentor Commented:
Seeing as this is either HS Chem or Freshman Chem... its largely memorizing / recognizing.
The paired / multiple atoms to a molecule comes from electron stability (Sulfur can exist as S8).

Largely, the 6A & 7A series.

Hydrogen
Nitrogen
Oxygen
Fluorine
Chlorine
Bromine
Iodine
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Infinity08Commented:
That should be :

    2 Na + I2 ---> 2 NaI

sodium (Na) with iodine (I2) forms sodium iodide (NaI)
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KelvinYConnect With a Mentor Commented:
Iodine atoms do not exist in isolation. Iodine forms molecules of I2 by covalent bonding. Since a molecule of I2 is the smallest unit that free iodine can exist as it is the base unit for any chemical equation involving iodine. So Infinity08's equation is spot on.
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dragonjimCommented:
Na + I2 ----> NaI

to balance properly, you need 2 Iodines on the products side:

Na + I2 ---> 2NaI

you now need to balance the Sodium.

2Na +I2 ---> 2NaI

FYI -- in I2, the 2 is a subscript indicating 2 iodine.
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dragonjimCommented:
Also -- must you verify the electrical charges balance... above we only showed the chemicals balance.

(to balance the charges) take each charge, multiple by the number  present.

2Na(1+) + I2(1-) --> 2NaI(no charge)
(2*1) + (2*-1) = (2*0)
2 + -2 = 0
0 = 0

balanced.
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c_hocklandAuthor Commented:
i guess my question is how am i suppose to know which ones comes on pair like iodine and which ones are not (especially when i am given words instaed of symbols)

any ideas ?
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Infinity08Connect With a Mentor Commented:
You can look it up :)

iodine is a halogen (check the periodic table), and the elemental form of halogens is always as diatomic molecules (ie. I2 in the case of iodine).

sodium however is an alkali metal (check the periodic table). In nature it doesn't occur very much in its elemental form.
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c_hocklandAuthor Commented:
that was great!! thanks so much
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dragonjimCommented:
Infinity08 -- I'm assuming this is for a course (either HS or Freshman College). In which case, C_Hockland may be required to identify the diatomic / etc on a quiz / test.

The ones you'll likely see on any such test, I listed above. As Infinity said, the Halogen (7A) always exist as diatomic. Other than that, the ones you see are the liquid / gas elements near the 7A.

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Infinity08Commented:
>> In which case, C_Hockland may be required to identify the diatomic / etc on a quiz / test.
Then my answer still stands : in order to know how different elements behave, and what their elemental forms are, the periodic table is "the bible". Just check it - it contains all information you'll need for this kind of stuff.
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