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Helium isn't a solid at absolute zero.
The temperature slider shows melting and boiling points at standard pressure. Unlike any other element, helium will remain liquid down to absolute zero at normal pressures. This is a direct effect of quantum mechanics: specifically, the zero point energy of the system is too high to allow freezing. At 2.5MPa, a very high pressure, it will become solid. Then again, so will almost every other element.
You misspelled cesium/aluminum.
When the USA submitted to the oversight of the International Union of Pure and Applied Chemistry (which allowed it to have some names for element 104-111, but not all of them), compromises were made. Aluminium is the British spelling, as is caesium. In exchange, the American spelling of sulfur (vs. sulphur) became the international standard.
Where are the Roman numeral group numbers like VIIB?
Roman numerals for groups were scrapped in 1990 by IUPAC because they're different and conflicting in the US and UK. If you're seeing them elsewhere, that source hasn't been updated in 30 years.
The valence numbers shown under Properties are not what I expected.
IUPAC's official definition of valence is, "The maximum number of univalent atoms (originally hydrogen or chlorine atoms) that may combine with an atom of the element under consideration, or with a fragment, or for which an atom of this element can be substituted." You may instead want the oxidation states shown on the Orbitals tab.
It's supposed to be atomic mass, not weight.
Atomic weight is the official term used by IUPAC to refer to the relative atomic masses published specifically for inclusion in periodic tables. The term is used because they are weighted averages.
Isn't it supposed to be Lanthanide, not -oid?
No, not according to IUPAC [PDF] (IR-3.5).
The electron configuration for an element is wrong.
Ptable shows true, experimental values for electron configuration. The method of drawing arrows you learned in class is a simplified method that works most of the time but has about 20 exceptions.
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