Protactinium

Protactinium is atom number 91 — every Protactinium atom has exactly 91 protons in its center, and that number is what makes it Protactinium and nothing else. Its symbol is Pa. At room temperature it is a solid.

Protactinium is a chemical element with symbol Pa and atomic number 91. It is a dense, silvery-gray metal which readily reacts with oxygen, water vapor and inorganic acids. It forms various chemical compounds where protactinium is usually present in the oxidation state +5, but can also assume +4 and even +2 or +3 states.

Summary from the source dataset, derived from Wikipedia (CC BY-SA 3.0) · original article

Protactinium sits in period 7, group 3 of the f-block. Its 91 electrons fill shells of 2, 8, 18, 32, 20, 9, 2 — written as [Rn] 5f2 6d1 7s2. Its electronegativity is 1.5 on the Pauling scale, and pulling the first electron off takes 568 kJ/mol. The outermost shell holds 2 electrons — the ones that do all the chemistry.

Full configuration: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f2 6d1
Ionization energies (kJ/mol): 568
Electron affinity: 53.03 kJ/mol · Electronegativity (Pauling): 1.5
Density: 15.37 g/cm³ · melts 1841 K · boils 4300 K

Values exactly as published — see where the data comes from.