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The atomic mass listed in the periodic is found by taking the average of all the different isotopes of a given element found in nature, weighted for their natural abundance.
Note that the atomic mass is not the same as the atomic weight. The atomic mass is the weight of one specific isotope of one atom, and is expressed in "atomic mass units" or amu. The atomic weight is expressed in grams per mole (g/mol) and is the weighted average of all the isotopes weighted by their abundance.
See the Web Links for more information about atomic mass and atomic weight.
Atomic masses of elements are not whole numbers because they are calculated based on the weighted average of the isotopes of an element, taking into account their abundance. Since isotopes have different masses due to varying numbers of neutrons, the weighted average results in a decimal Atomic Mass for most elements.
The main reason that the atomic mass of elements is not a whole number is due to the presence of different isotopes - these have the same number of protons in the nucleus but a different number of neutrons - so their masses are different even though chemically they are identical.
The two isotopes of Chlorine are 35Cl- (75.77%) and 37Cl (24.23%) giving an overall "average" mass of 35.4527.
The atomic weights of some elements are averages, this is because some elements have different isotopes (same number of protons but a different number of neutrons) For example, chlorine has an atomic mass of 35.5 this is because if you were to take a sample of chlorine approximately 75% of the chlorine atoms in that sample would have an atomic mass of 35 and 25% would have a mass of 37 this gives and average of 35.5 and explains why the atomic weights of elements aren't integers.
Some of the elements in the Periodic Table are not whole numbers because it is the weighted average mass of all the different isotopes of that particular element, e.g the stated atomic mass for carbon takes into account carbon-12 (about 99%), carbon-13 (about 1%), and carbon-14 (trace amounts) to come up with about 12.011. Also, except for carbon-12, the mass even for a specific isotope is not a whole number due to two factors: 1) neutrons are slightly more massive than protons; 2) nuclear binding energy throws the mass off slightly. (Carbon-12 is the standard and has a mass of exactly 12 by definition.)
Atomic masses of elements are usually not whole numbers because of isotopes.
Elements tend to exist as more than one isotope, so the atomic mass in the corner is a weighted average of all of the isotopes an element exists as.
The atomic mass of an element listed on the periodic table is a weighted average of all of the naturally-occurring isotopes, which have different numbers of neutrons and therefore different masses.
Some elements have isotopes, isotopes are the same element (just with a different mass, so the same number of protons but more/less neutrons)
Most isotopes are unstable so are not is taken into consideration when calculating the RAM.
Take silicon as an example only three isotopes are stable;
28Si - 92.23%
29Si - 4.67%
30Si - 3.1%
For the element Si with the naturally occurring isotopes 28Si, 29Si, 30Si, and with the respective abundances of A%, B%, C% etc,
r.a.m. = (A/100 x a) + (B/100 x b) + (C/100 x c)
r.a.m. = ((92.23/100)*28) + ((4.67/100)*29) + ((3.1/100)*30)
r.a.m. = 28.1087
(RAM given by my data book is 28.1)
As an example, most calcium is calcium-40 with 20 protons and 20 neutrons. But about 3% of naturally occurring calcium has more neutrons, as calcium-41 through 44, 46, and 48. The atomic weight is given as 40.078 on the periodic table.
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How are the atomic numbers and the atomic masses of the elements related to how the elements are arranged on peridoic table?
The atomic number of an element is the number of protons in its nucleus, while the atomic mass is the average mass of the isotopes of that element. Elements on the periodic table are arranged in order of increasing atomic number, which also corresponds to the number of electrons in a neutral atom of that element. The periodic table is structured based on these increasing atomic numbers, with elements organized into groups and periods based on similarities in their properties.
The current standard for atomic masses is?
The current standard for atomic masses is based on the Carbon-12 isotope. It is defined as exactly 12 atomic mass units (amu), with all other atomic masses determined relative to it. This standard allows for consistency in measurements and comparisons of atomic masses across different elements.
How do atomic numbers and atomic masses increase in the periodic table?
Atomic numbers increase from left to right across a period on the periodic table. This is because each element in a period has one more proton in its nucleus compared to the element before it. Atomic masses generally increase from left to right as well, but there may be deviations due to isotopes or other factors. Within a group or column, atomic numbers and atomic masses increase from top to bottom as each successive element has more electrons and neutrons than the one above it.
Which term describes atoms with different atomic masses due to varying numbers of neutrons?
Isotopes describe atoms with different atomic masses due to varying numbers of neutrons.
What are atoms of the same element thay have different atomic masses?
Atoms of the same element that have different atomic masses are called isotopes. Isotopes of an element have the same number of protons but different numbers of neutrons. This results in variations in atomic mass while maintaining the same chemical properties.
Why aren't atomic masses of elements not whole numbers?
because of its no. in table of elements
Why don27t elements in the periodic table have whole numbers for their atomic masses?
Because the masses of protons, neutrons and electrons are not whole numbers.
Why the atomic mass numbers listed for elements on the Periodic Table are not whole numbers.?
Why are atomic masses of elements not generally whole numbers? The atomic masses listed on the periodic table are a weighted AVERAGE of an element'sisotopes. ... An element's atomic number is the number of protons in its nucleus. Number of protons specifies atom type.
How are the atomic numbers and the atomic masses of the elements related to how the elements are arranged on peridoic table?
The atomic number of an element is the number of protons in its nucleus, while the atomic mass is the average mass of the isotopes of that element. Elements on the periodic table are arranged in order of increasing atomic number, which also corresponds to the number of electrons in a neutral atom of that element. The periodic table is structured based on these increasing atomic numbers, with elements organized into groups and periods based on similarities in their properties.
What are the three pairs of elements that are out of order in the periodic table in terms of their atomic masses. Why it is necessary to invert their order in the table?
The three pairs of elements that are out of order in terms of their atomic masses are iodine and tellurium, cobalt and nickel, and uranium and neptunium. It is necessary to invert their order in the table to maintain the order of increasing atomic masses within each group or period, ensuring that elements with consecutive atomic numbers also have consecutive atomic masses.
Which two elements have an atomic mass less than twice their atomic number?
Elemental hydrogen and helium have atomic masses less than twice their atomic numbers.
What did Dimitri Mendeleeve do?
Dmitri arranged the elements in order of increasing atomic masses. He arranged elements in rows and columns according to atomic masses.
Why could you use clues about atomic mass to place elements even though the table is now based on atomic number?
the bigger the mass of an element, the higher its atomic number.
What are the atomic number and mass of the animals?
Animals do not have atomic numbers and masses. Those properties are specific to elements on the periodic table.
When masses combine to form elements with larger masses?
Atomic fusion occurs when masses combine to form elements with larger mass.
What elements have such small masses that they are not even considered when atomic masses are calculated?
Electrons
Why does the atomic mass of some elements is shown as a decimal value?
Many atoms exist in the form of different isotopes. These have different numbers of neutrons and so their atomic masses are different. The atomic mass for the element is the average of these masses, weighted together according to their abundance.
