Beryllium

Beryllium is atom number 4 — every Beryllium atom has exactly 4 protons in its center, and that number is what makes it Beryllium and nothing else. Its symbol is Be. At room temperature it is a solid.

Beryllium is a chemical element with symbol Be and atomic number 4. It is created through stellar nucleosynthesis and is a relatively rare element in the universe. It is a divalent element which occurs naturally only in combination with other elements in minerals.

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

Beryllium sits in period 2, group 2 of the s-block. Its 4 electrons fill shells of 2, 2 — written as [He] 2s2. Its electronegativity is 1.57 on the Pauling scale, and pulling the first electron off takes 899.5 kJ/mol. The outermost shell holds 2 electrons — the ones that do all the chemistry.

Full configuration: 1s2 2s2
Ionization energies (kJ/mol): 899.5, 1757.1, 14848.7, 21006.6
Electron affinity: -48 kJ/mol · Electronegativity (Pauling): 1.57
Density: 1.85 g/cm³ · melts 1560 K · boils 2742 K

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