Two atoms of Argon (z = 18) have atomic weights 38 and 40. The number of electrons in
their atoms is
Answers
Mass no of Argon is 40 so
For atomic weight 38 - There are 16 electrons
For atomic weight 40 - There are 18 electrons
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Explanation:
An element's atomic mass is best thought of as the weighted average of the atomic masses of its stable isotopes.
As you know, the identity of a chemical element depends exclusively on the number of protons an atom has in its nucleus - this is known as atomic number.
In this case, you know for a fact that any atom that has
19
protons in its nucleus will be an atom of argon.
However, the number of neutrons an atom can have and still retain its chemical identity can vary quite significantly.
The atom you listed in the question is actually argon-40, an isotope of argon that has a mass number equal to
40
. This implies that it will also have
mass number
=
A
=
Z
+
no. of neutrons
no. of neutrons
=
A
−
Z
=
40
−
18
=
22
This isotope of argon has
22
neutrons in its nucleus. But this is just one isotope of argon. Argon has a total of
24
isotopes, out of which three are stable and contribute to its average atomic mass.
Each stable isotope has an abundance associated with it. The average atomic mass of the element argon will be
avg. atomic mass
=
∑
i
(
isotope
i
×
abundance
i
)
The atomic masses of argon's stable isotopes and their respective abundances can be found here:
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