Mass number is term used for isotopes, not for elements.
And it is boring to list here all the isotopes of the first 20 elements.
H -->+1 He --> 0 Be --> B
Sc, scandium (21), the first metal element in the 3d-block (transition elements); next to calcium (20).
The mass number of a conventionally named isotope is the number after the hyphen; in this instance, 20.
Atomic number 20 therefore 20 protons and 20 electrons. Mass number 45 therefore 45-20 = 25 neutrons.
Sodium is a metal element. Atomic mass number of it is 23.
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H -->+1 He --> 0 Be --> B
The mass number of a conventionally named isotope is the number after the hyphen; in this instance, 20.
Sc, scandium (21), the first metal element in the 3d-block (transition elements); next to calcium (20).
Atomic number 20 therefore 20 protons and 20 electrons. Mass number 45 therefore 45-20 = 25 neutrons.
Sodium is a metal element. Atomic mass number of it is 23.
Approx. 20 elements were known in 1800.
You actually just answered your own question. The Isotope Ar-37 has a mass of 37. Most elements and Isotopes are commonly phrased like "Element-Mass"
Answer: 20 Details: mass number - atomic number = number of neutrons.
The first 20 elements are Hydrogen, Helium, Lithium, Beryllium, Boron, Carbon, Nitrogen,Oxygen, Flourine,Neon,Sodium,Magnesium, Aluminium,Silicon,Phosporous,Sulphur, Chlorine, Argon, Pottasium, and Calcium. The numbers on the top right are the mass of the element.
There is no such noble gas with an atomic mass of 30. The mass of neon is 20 and the mass of the next noble gas, argon, is 40
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