Neptunium

Neptunium is atom number 93 — every Neptunium atom has exactly 93 protons in its center, and that number is what makes it Neptunium and nothing else. Its symbol is Np. At room temperature it is a solid.

Neptunium is a chemical element with symbol Np and atomic number 93. A radioactive actinide metal, neptunium is the first transuranic element. Its position in the periodic table just after uranium, named after the planet Uranus, led to it being named after Neptune, the next planet beyond Uranus.

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

Neptunium sits in period 7, group 3 of the f-block. Its 93 electrons fill shells of 2, 8, 18, 32, 22, 9, 2 — written as [Rn] 5f4 6d1 7s2. Its electronegativity is 1.36 on the Pauling scale, and pulling the first electron off takes 604.5 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 5f4 6d1
Ionization energies (kJ/mol): 604.5
Electron affinity: 45.85 kJ/mol · Electronegativity (Pauling): 1.36
Density: 20.45 g/cm³ · melts 912 K · boils 4447 K

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