The noble gases (Helium, Neon, Argon etc.) were not discovered until much later, which explains why there was a periodicity of 7 and not 8 in Newlands table. Newlands did not leave any gaps for ...

Across a period from left to right, the covalent radius decreases. As you move from left to right across the periodic table, atoms have more electrons in their outer energy level and more protons ...

How often the observations of a time series occur is called the sampling frequency or the periodicity of the series. For example, a time series with one observation each month has a monthly sampling ...