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This is because of the existence of isotopes. What's an isotope? It's an element that has a specific number of neutrons. I'll give an example. Carbon has 6 Neutrons, 6 Protons, 6 Electrons.
That's the most common form of Carbon. But 1% of all Carbon is an isotope that has 1 extra Neutron. So it weighs 1 more, also. So this isotope weighs 13 instead of 12. We call it Carbon 13, or 13C.
There's also a 14C and so on....but in far smaller amounts.
So anyhow, since we have 99% Carbon weighing 12 and 1% Carbon weighing 13, what weight do we put on our Periodic Table?
Well, I guess we could put the most common.
But what about Bromine? That has 2 major isotopes. One weighs 79 and the other 81, they are 51% and 49% (very roughly) abundant respectively.
That's almost an exact split...it'd be pretty ridiculous to only put the weight of one.
So instead we say it's weight is 79.9...which is it's weight averaged over all of it's isotopes, with respect to their abundance.
It doesn't seem right to average it on an atom-to-atom basis. But if I'm weighing 2grams of my sample, there are HUGE numbers of molecules there. And the only way I can do an accurate calculation is to know an averaged mass, because my sample WILL contain all of the isotopes.
If I calculate for only 1 isotopic weight, my calculations will be wrong. That's why we average them.
Kasandra Hegmann
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∙ 13y agoBasically for convenience, to avoid using powers of 10 as part of numbers more often than necessary; there is no commonly accepted prefix for the basic mass unit "gram" to make the mass of a single atom greater than a small fraction of such a unit.
Wiki User
∙ 11y agoSubatomic particles are not measured by their weight in a scientific situation; they are measured by their rest masses in most cases or by their relativistic mass if they are interacting in a collision.
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∙ 12y agoThe average atomic weight of a chemical element take into account the isotopic composition and the atomic masses of these isotopes.
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∙ 11y agoThe atomic weights (not mass !) of chemical elements are related to 1/12 of the mass of the isotope carbon-12 in the ground state (the Atomic Mass unit).
Wiki User
∙ 8y agoThey are calculated the ratio of the average mass of one atom of an element to one twelfth of the mass of an atom of carbon-12.
Wiki User
∙ 14y agoBoth have a basis of carbon-12
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Is the atomic mass equal to the number of atoms in the elements?
The mass number of an isotope of an element is equal to its atomic mass number. However, the atomic weight of an element is a weighted average of the isotopes that occur in the element in nature. Because almost all elements have more than one naturally occurring isotope (if they have any), the atomic weights of most elements are not integers, as mass numbers always are.
The atomic weight of Br is the of the atomic weights of Cl and l?
Average :]
What is the atomic weight of the element Tantalum?
The relative atomic mass is 180.948
How did Mendeleyev organize the periodic table of elements?
In increasing order of atomic weights.
Atoms that have the same atomic numbers but different atomic weights are called what?
If they have the same atomic number but different mass, then they have a different number of neutrons, and they are called ISOTOPES.
To which element are all atomic weights relative?
That would be Carbon (C). Which has a designated mass of 12.
Base weight a system of comparing atomic weights to carbon is it true or false?
True. The unit for the atomic weights of chemical elements is the relative atomic mass unit (1/12 from the atomic mass of the isotope 12C). Note that atomic weights is used for elements and atomic mass for isotopes.
Is it true that The atomic weight is only an average of relative weights of an atom and its isotopes and it may vary from the weight of a specific isotope?
True
Why do atomic weights are in fraction?
Because atomic weights must be measured in fractions.
How relative atomic mass is related to gram?
relative Atomic Mass
How the relative atomic mass is related to gram?
relative atomic mass
Why are atomic weights realitive weights?
Actually weights are too small and are hard to work with.
How is atomic mass caluclated?
It is approximately equivalent to the number of protons and neutrons in the atom (the mass number) or to the average number allowing for the relative abundances of different isotopes.
What is the relative atomic mass of potassium?
the relative atomic mass for the element potassium is 39.0983
Is the atomic mass equal to the number of atoms in the elements?
The mass number of an isotope of an element is equal to its atomic mass number. However, the atomic weight of an element is a weighted average of the isotopes that occur in the element in nature. Because almost all elements have more than one naturally occurring isotope (if they have any), the atomic weights of most elements are not integers, as mass numbers always are.
The atomic weight of Br is the of the atomic weights of Cl and l?
Average :]
What is often used in place of atomic weights?
Atomic Mass Number
