Because of the radiasion
Mendeleev calculated atomic number by increasing atomic number, which match the number of protons in an atomic nucleus of a single element
Do you think at atomic radius ? Zr calculated atomic radius: 206 pm, Hf calculated atomic radius: 208 pm. Or atomic mass? Zr: 91,224, Hf: 178,49.
10.81
Atomic mass is determined by mass spectrometry.
The atomic radius is calculated by spctroscopic or X-ray methods.
Neon is a non meta element. Atomic mass of it is 20. Atomic number of it is 10.
Samarium has a calculated atomic radius of 238 pm.
electron equals the atomic number
By subtracting the mass number and the atomic number, the number of neutrons can be calculated.
They experimented with xrays on the prisoners in the concentration camps. Mostly at Auschwitz.
I just got my xrays taken for my left knee, it was four xrays for $100, it may be more other places