chemistry help asap easy questions PLEASE HELP URGENT

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tayk477
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One molecule of a diatomic element has a mass of 6.310 × 10−23 g. The molecule contains 20 neutrons. Identify the element.
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cata03
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(Original post by tayk477)
One molecule of a diatomic element has a mass of 6.310 × 10−23 g. The molecule contains 20 neutrons. Identify the element.
If it has mass 6.310x10^-23 g then you know that one mol of the element will be 37.99g (by multiplying by avogadro’s constant). Half this to get the Ar of one atom - 19. You know that there are 10 nuetrons in each atom so you are looking for an atom with an Ar of 19 and an atomic number of 9 (as there must be 9 protons as 19-10=9)

the element must therefore be F, which makes sense as fluorine is diatomic
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tony_dolby
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Have they give you the value of the atomic mass unit somewhere? Aha, I see the previous poster has solved it much more easily!
Last edited by tony_dolby; 1 month ago
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tayk477
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(Original post by cata03)
If it has mass 6.310x10^-23 g then you know that one mol of the element will be 37.99g (by multiplying by avogadro’s constant). Half this to get the Ar of one atom - 19. You know that there are 10 nuetrons in each atom so you are looking for an atom with an Ar of 19 and an atomic number of 9 (as there must be 9 protons as 19-10=9)

the element must therefore be F, which makes sense as fluorine is diatomic
(Original post by tony_dolby)
Have they give you the value of the atomic mass unit somewhere? Aha, I see the previous poster has solved it much more easily!
that helps thanks so much, im doing past papers and this one is challenging:

Which of the following best describes the O-N-O bond angle an the NO2− ion?
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tony_dolby
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The structure of NO2 is complicated. Four of the electrons in N involved in bonding to the oxygens, and there is a single unpaired electron on the N. Adding an electron to form the nitrite ion NO2- means that there are now three electrons pairs to be considered according to VSEPR. Remember that double bonds count as one bonding electron pair in VSEPR.

Three electron pairs should be 120 degrees apart if they repelled equally, but lone pair bond pair repulsion is greater than bond pair - bond pair repulsion. Therefore the O-N-O bond angle is less than 120. The exact figure is 115 degrees, but I suspect anything just below 119 would score.
Last edited by tony_dolby; 1 month ago
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tayk477
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could you check your messages please? thanks


(Original post by tony_dolby)
The structure of NO2 is complicated. Four of the electrons in N involved in bonding to the oxygens, and there is a single unpaired electron on the N. Adding an electron to form the nitrite ion NO2- means that there are now three electrons pairs to be considered according to VSEPR. Remember that double bonds count as one bonding electron pair in VSEPR.

Three electron pairs should be 120 degrees apart if they repelled equally, but lone pair bond pair repulsion is greater than bond pair - bond pair repulsion. Therefore the O-N-O bond angle is less than 120. The exact figure is 115 degrees, but I suspect anything just below 119 would score.
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tayk477
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does anyone know what working out I would use for this?
which of the following have significant bond dipoles, but no molecular dipoles?

1) benzene 2) tetrachloromethane 3) sulfur dioxide 4) phosphorus pentachloride 5) dichloromethane
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cata03
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(Original post by tayk477)
does anyone know what working out I would use for this?
which of the following have significant bond dipoles, but no molecular dipoles?

1) benzene 2) tetrachloromethane 3) sulfur dioxide 4) phosphorus pentachloride 5) dichloromethane
I think the answer is 2. Think about the shape of the molecule - although there are dipoles on each of the bonds, the molecules is symmetrical so they cancel out to give no overall molecular dipole
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Rara345
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(Original post by cata03)
If it has mass 6.310x10^-23 g then you know that one mol of the element will be 37.99g (by multiplying by avogadro’s constant). Half this to get the Ar of one atom - 19. You know that there are 10 nuetrons in each atom so you are looking for an atom with an Ar of 19 and an atomic number of 9 (as there must be 9 protons as 19-10=9)

the element must therefore be F, which makes sense as fluorine is diatomic
Hey, would you mind pls writing out the equation you used for the firt step?
The only one I can think of is No molecules = moles * avagadro but I don't think thats the one you used as it donest have mass?
ty
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