## How many significant figures? [ENDORSED]

H-Atom ($E_{n}=-\frac{hR}{n^{2}}$)

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Isabel Jabara 1C
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Joined: Fri Apr 06, 2018 11:03 am

### How many significant figures?

On one of the UA's practice tests (Lyndon's), question 7a asked "An excited hydrogen atom undergoes an electronic transition from n=3 to n=1. Calculate the frequency of the photon emitted." Since the question only contains numbers with 1 significant figure, should we answer with only one?

Elijah E 1C
Posts: 15
Joined: Fri Apr 06, 2018 11:02 am

### Re: How many significant figures?

Since these numbers reference atomic energy level and cant be any non-integer I don't think they effect sig figs. That being said I would give the exact value.

danielruiz1G
Posts: 62
Joined: Fri Apr 06, 2018 11:04 am

### Re: How many significant figures?

Just remember to use the rules of sig figs when either multiplying/dividing or adding/subtracting. With multi./division you keep the same number of digits as the smallest number of sig figs in your problem and for addition/subtraction, you keep the sig fig until the digit of the least accuracy.

Chris Qiu 1H
Posts: 31
Joined: Fri Apr 06, 2018 11:04 am

### Re: How many significant figures?

I'd keep 3-4 sig figs just to be safe. Having only one sig fig for a value that wont be a whole number (or a single digit for that manner) doesn't make too much sense.

Chem_Mod
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### Re: How many significant figures?

Isabel Jabara 1C wrote:On one of the UA's practice tests (Lyndon's), question 7a asked "An excited hydrogen atom undergoes an electronic transition from n=3 to n=1. Calculate the frequency of the photon emitted." Since the question only contains numbers with 1 significant figure, should we answer with only one?

Use the number of sig figs given by the constants that you used. For example, planck's constant will be given with a certain number of sig figs.

Chem_Mod
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### Re: How many significant figures?  [ENDORSED]

n=1 and n=3 are values whose sig figs we DO NOT take into account because we know the EXACT value of these.

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