Sodium

Sodium is atom number 11 — every Sodium atom has exactly 11 protons in its center, and that number is what makes it Sodium and nothing else. Its symbol is Na. At room temperature it is a solid.

Sodium /ˈsoʊdiəm/ is a chemical element with symbol Na (from Ancient Greek Νάτριο) and atomic number 11. It is a soft, silver-white, highly reactive metal. In the Periodic table it is in column 1 (alkali metals), and shares with the other six elements in that column that it has a single electron in its outer shell, which it readily donates, creating a positively charged atom - a cation.

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

Sodium sits in period 3, group 1 of the s-block. Its 11 electrons fill shells of 2, 8, 1 — written as [Ne] 3s1. Its electronegativity is 0.93 on the Pauling scale, and pulling the first electron off takes 495.8 kJ/mol. The outermost shell holds 1 electron — the ones that do all the chemistry.

Full configuration: 1s2 2s2 2p6 3s1
Ionization energies (kJ/mol): 495.8, 4562, 6910.3, 9543, 13354, 16613, 20117, 25496 … (11 published)
Electron affinity: 52.867 kJ/mol · Electronegativity (Pauling): 0.93
Density: 0.968 g/cm³ · melts 370.944 K · boils 1156.09 K

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