Molybdenum

Molybdenum is atom number 42 — every Molybdenum atom has exactly 42 protons in its center, and that number is what makes it Molybdenum and nothing else. Its symbol is Mo. At room temperature it is a solid.

Molybdenum is a chemical element with symbol Mo and atomic number 42. The name is from Neo-Latin molybdaenum, from Ancient Greek Μόλυβδος molybdos, meaning lead, since its ores were confused with lead ores. Molybdenum minerals have been known throughout history, but the element was discovered (in the sense of differentiating it as a new entity from the mineral salts of other metals) in 1778 by Carl Wilhelm Scheele.

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

Molybdenum sits in period 5, group 6 of the d-block. Its 42 electrons fill shells of 2, 8, 18, 13, 1 — written as [Kr] 4d5 5s1. Its electronegativity is 2.16 on the Pauling scale, and pulling the first electron off takes 684.3 kJ/mol. The outermost shell holds 1 electron — the ones that do all the chemistry.

Full configuration: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1 4d5
Ionization energies (kJ/mol): 684.3, 1560, 2618, 4480, 5257, 6640.8, 12125, 13860 … (30 published)
Electron affinity: 72.1 kJ/mol · Electronegativity (Pauling): 2.16
Density: 10.28 g/cm³ · melts 2896 K · boils 4912 K

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