# GCSE Chemistry help

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Does the periodic table show the mass number for each element or the relative atomic mass?

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#3

The bigger number is the mass number (the total number of the protons and neutrons in an atom) The atmoic number is the number of electrons and protons.

To work out the realative atomic mass:

(Relative abundance of isotope 1 x mass number) + (Relative abundance of isotope 2

x mass number) Divided by 100

To work out the realative atomic mass:

(Relative abundance of isotope 1 x mass number) + (Relative abundance of isotope 2

x mass number) Divided by 100

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(Original post by

The bigger number is the mass number (the total number of the protons and neutrons in an atom) The atmoic number is the number of electrons and protons.

To work out the realative atomic mass:

(Relative abundance of isotope 1 x mass number) + (Relative abundance of isotope 2

x mass number) Divided by 100

**DiamondsForever**)The bigger number is the mass number (the total number of the protons and neutrons in an atom) The atmoic number is the number of electrons and protons.

To work out the realative atomic mass:

(Relative abundance of isotope 1 x mass number) + (Relative abundance of isotope 2

x mass number) Divided by 100

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#6

(Original post by

But then how can chlorine have mass number of 35.5? this is not a whole number?

**cherrypiez**)But then how can chlorine have mass number of 35.5? this is not a whole number?

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It doesn't matter. What's the question, what's the other isotope?

**DiamondsForever**)It doesn't matter. What's the question, what's the other isotope?

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Chlorine has a mass number of 35.5 because it is an average of the different isotopes of chlorine.

**hadeelxxo**)Chlorine has a mass number of 35.5 because it is an average of the different isotopes of chlorine.

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(Original post by

Oh okay well its just because chlorine has 2 isotopes, its just decimals

**DiamondsForever**)Oh okay well its just because chlorine has 2 isotopes, its just decimals

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#11

(Original post by

So how do you calculate the mass number of chlorine if it has more than one isotopes? What's the formula for it? I know that to find it you need to add the number of protons and neutrons, but how do you take into account the other isotopes?

**cherrypiez**)So how do you calculate the mass number of chlorine if it has more than one isotopes? What's the formula for it? I know that to find it you need to add the number of protons and neutrons, but how do you take into account the other isotopes?

Chlorine atoms contain 17 protons and 17 electrons. About 75 per cent of chlorine atoms have 18 neutrons, while about 25 per cent have 20 neutrons because of the two different isotopes

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#12

Chlorine has 2 isotopes Cl-35 and Cl-37.

The mass number of an element is the average mass of all the existing isotopes. Roughly the ratio of abundance of Cl-35 to the abundance of Cl-37 is 3:1.

Accordingly, calculated is calculated as:

(3 x 35) + (37)

-------------------- = 35.5.

3+1

That's it.

The mass number of an element is the average mass of all the existing isotopes. Roughly the ratio of abundance of Cl-35 to the abundance of Cl-37 is 3:1.

Accordingly, calculated is calculated as:

(3 x 35) + (37)

-------------------- = 35.5.

3+1

That's it.

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(Original post by

Chlorine atoms contain 17 protons and 17 electrons. About 75 per cent of chlorine atoms have 18 neutrons, while about 25 per cent have 20 neutrons because of the two different isotopes

**hadeelxxo**)Chlorine atoms contain 17 protons and 17 electrons. About 75 per cent of chlorine atoms have 18 neutrons, while about 25 per cent have 20 neutrons because of the two different isotopes

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(Original post by

Chlorine has 2 isotopes Cl-35 and Cl-37.

The mass number of an element is the average mass of all the existing isotopes. Roughly the ratio of abundance of Cl-35 to the abundance of Cl-37 is 3:1.

Accordingly, calculated is calculated as:

(3 x 35) + (37)

-------------------- = 35.5.

3+1

That's it.

**DiamondsForever**)Chlorine has 2 isotopes Cl-35 and Cl-37.

The mass number of an element is the average mass of all the existing isotopes. Roughly the ratio of abundance of Cl-35 to the abundance of Cl-37 is 3:1.

Accordingly, calculated is calculated as:

(3 x 35) + (37)

-------------------- = 35.5.

3+1

That's it.

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#15

Here's the formula:

(Relative abundance of isotope 1 x mass number) + (Relative abundance of isotope 2 x mass number)

--------------------------------------------------------------------------------------------------------------------------------

100

(Relative abundance of isotope 1 x mass number) + (Relative abundance of isotope 2 x mass number)

--------------------------------------------------------------------------------------------------------------------------------

100

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#16

(Original post by

so how do scientists know which is the original one? shouldn't it be the one with 18 neutrons as there is 75% of it?

**cherrypiez**)so how do scientists know which is the original one? shouldn't it be the one with 18 neutrons as there is 75% of it?

They just work out an average they're both original. Btw are you doing Core science or additional?

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(Original post by

They just work out an average they're both original. Btw are you doing Core science or additional?

**DiamondsForever**)They just work out an average they're both original. Btw are you doing Core science or additional?

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#18

Me too! No there is no formula for mass number, mass number is just the largest number (the number at the top of the element)

All you need to know is the formula for relative atomic mass and then the question will say what the relative abundance is, you just have to work out the relative atomic mass using the formula that I mentioned in the above posts.

All you need to know is the formula for relative atomic mass and then the question will say what the relative abundance is, you just have to work out the relative atomic mass using the formula that I mentioned in the above posts.

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#19

**cherrypiez**)

so how do scientists know which is the original one? shouldn't it be the one with 18 neutrons as there is 75% of it?

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(Original post by

Me too! No there is no formula for mass number, mass number is just the largest number (the number at the top of the element)

All you need to know is the formula for relative atomic mass and then the question will say what the relative abundance is, you just have to work out the relative atomic mass using the formula that I mentioned in the above posts.

**DiamondsForever**)Me too! No there is no formula for mass number, mass number is just the largest number (the number at the top of the element)

All you need to know is the formula for relative atomic mass and then the question will say what the relative abundance is, you just have to work out the relative atomic mass using the formula that I mentioned in the above posts.

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