Atomic mass number question.

In summary: Not exactly. The molar mass is a weighted average based on an element's isotope mass and it's relative abundancy and slight mass deficits (or overage) due to nucleon binding energy for elements other than carbon 12.Well in my first week course in chemistry, we calculated molar mass using those figures...?What does your periodic table list for the molar mass of chlorine? Mine is 35.453. This is because natrually occurring chlorine comes in two flavors... one weighs ~35 amu (about 75% abundance) and the other weighs ~37 amu (about 25% abundance). The weighted average of these two isotopes yields the atomic weight of 35.453.But what I don
  • #1
Joza
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On the P.T.E., the atomic mass number of an element gives the number of protons and neutrons in its nucleus, ie. the number of particles in its nucleus. But this number also gives that particular elements molar mass, correct? eg. For carbon, it has 12 particles in its nucleus, and its molar mass is 12g, that is, 12g of Carbon 12 will have 6.022 times 10^23 atoms. Both of these come from its atomic mass number, 12.

How does the atomic mass number give both of these?
 
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  • #2
Joza said:
On the P.T.E., the atomic mass number of an element gives the number of protons and neutrons in its nucleus, ie. the number of particles in its nucleus. But this number also gives that particular elements molar mass, correct?

Not exactly. The molar mass is a weighted average based on an element's isotope mass and it's relative abundancy and slight mass deficits (or overage) due to nucleon binding energy for elements other than carbon 12.
 
  • #3
Well in my first week course in chemistry, we calculated molar mass using those figures...?
 
  • #4
What does your periodic table list for the molar mass of chlorine? Mine is 35.453. This is because natrually occurring chlorine comes in two flavors... one weighs ~35 amu (about 75% abundance) and the other weighs ~37 amu (about 25% abundance). The weighted average of these two isotopes yields the atomic weight of 35.453.
 
  • #5
But what I don't understand, is how you can use the atomic mass number for molar weight.

How does the atomic mass contain Avogadro's number of atoms when used for molar weight, AND number of particles in nucleus?
 
  • #7
Lets use hydrogen as an example, hydrogens molar mass is ~1g, this is to say, that 6.02*10^23 hydrogen atoms have a mass of 1g, the molecular mass of a Hydrogen atom is ~1/6.02*10^23 = ~1.66*10^-24, this mass doesn't encooperate electrons or isotopes in my case, cooincidently, this mass is also equal too the mass of one proton, the mass of a proton is equal too the mass of a neutron, the value 1.66*10^-24 is roughly equivalent to 1u, an atomic mass unit.

Now as for any element appearing to match up to the number of protons/neutrons in it, this is because a mole is a humanly derived quantity, a mole is 6.02*10^23 atoms, we use it for sake of ease, it is defined as the amount of substance that contains as many elementry entities as there are atoms in 12g of carbon-12.

Carbon-12 has 12 elementry particles (6Protons 6Neutrons), 1g of the 12g that Carbon-12 is made of is equivalent to the molar mass of a neutron or proton, which is why they "match up", everytime you go up 1g in molar mass, your effectively adding 1mole of protons or neutrons.

If you divide this extra mole of protons or neutrons by avagadros constant, you end up with a singular unit of the proton or neutron, so for an example, dividing carbon-12's molar mass (12g) by 6.02*10^23, your effectively finding out the molecular mass of 6 protons and 6 neutrons, much like if you divided the mass of 1g of Hydrogen, your finding the molecular mass of 1 Proton because hydrogen contains 1 Proton, and 1 mole of Hydrogen is 6.02*10^23 protons.

The molecule is created by the laws of physics, moles are a quantity of molecules created by man in order to make calculations easier, because if we went around stating everything in terms of the amount of molecules it contained, rather then moles, or kilograms, we would be stating massive numbers.

EDIT: A better way of putting it is that a mole is the "Gram weight" of a molecule, so if a molecule weights 12u, then its molar mass is 12g, which is 6.02*10^23*12u molecules
 
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1. What is atomic mass number?

Atomic mass number is the total number of protons and neutrons in the nucleus of an atom. It is represented by the symbol A.

2. How is atomic mass number different from atomic number?

Atomic number is the number of protons in an atom's nucleus, while atomic mass number is the total number of protons and neutrons. Atomic number is used to identify and classify elements, while atomic mass number is used in calculations involving isotopes.

3. How is atomic mass number calculated?

Atomic mass number is calculated by adding the number of protons and neutrons in an atom's nucleus. The number of protons can be found on the periodic table, while the number of neutrons can be calculated by subtracting the atomic number from the atomic mass number.

4. Why is atomic mass number a decimal number?

Atomic mass number is a decimal number because it takes into account the average mass of all the isotopes of an element. Isotopes are atoms of the same element with different numbers of neutrons, which affects the overall mass of the atom.

5. How does atomic mass number affect an atom's properties?

Atomic mass number does not directly affect an atom's properties. However, the number of protons and neutrons in the nucleus can affect the stability of the atom, which can in turn affect its reactivity and other properties.

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