Tin at a glance
- Atomic number
- 50
- Symbol
- Sn
- Atomic mass
- 118.71 u
- Category
- Post-transition metal
- Group / period
- 14 / 5
- Electron configuration
- [Kr] 4d 10 5s 2 5p 2
- State at 25 °C
- Solid
- Melting point
- 231.9 °C
- Boiling point
- 2602 °C
- Density
- 7.287 g/cm³
- Electronegativity
- 1.96
- 1st ionization energy
- 709 kJ/mol
- Oxidation states
- +4, +2
- Discovered
- Antiquity
Atomic structure
A neutral tin atom has 50 protons and 50 electrons, and its most common isotope carries about 70 neutrons. One atom weighs about 1.97 × 10⁻²⁵ kg, so a mole of tin (6.022 × 10²³ atoms) weighs 118.71 g. That nucleus holds 1.4 neutrons for every proton. Its symbol Sn comes from stannum. The electrons fill 5 shells (K 2, L 8, M 18, N 18, O 4), which gives the configuration [Kr] 4d 10 5s 2 5p 2. With 4 electrons in its outer shell, it usually shares electrons in covalent bonds. It has 10 stable isotopes: Sn-112, Sn-114, Sn-115, Sn-116, Sn-117, Sn-118, Sn-119, Sn-120, Sn-122 and Sn-124. Its most common isotope, Sn-120, has the same mass number as Te-120: isobars, nuclei of different elements with 120 nucleons each.
Physical properties
At room temperature (25 °C) tin is a solid. It melts at 231.9 °C and boils at 2602 °C, so it stays liquid across a 2370-degree range. It stays solid in boiling water but would melt in a hot kitchen oven. Its density is 7.287 g/cm³, 7.29 times as dense as water. Its atoms have a radius of about 145 pm (Indium next door is 155 pm). In the solid, its atoms pack into a tetragonal lattice.
Chemical behaviour
Its electronegativity is 1.96 on the Pauling scale. Pulling off its outermost electron takes 709 kJ/mol, less than Germanium above it (762 kJ/mol). A bond between tin and chlorine would be polar covalent, with an electronegativity difference of 1.2. It releases 107 kJ/mol when it gains an extra electron. Its common oxidation states are +4, +2, so in compounds you will usually meet it as Sn⁴⁺ and Sn²⁺. Group 14 also holds Carbon, Silicon, Germanium, Lead and Flerovium, which share its outer-shell pattern. Its Lewis symbol is Sn surrounded by 4 dots.
Where it comes from
It makes up 2.3 mg/kg of Earth's crust, the 51st most abundant element there. In the human body it accounts for about 0.00002 % of body mass. It has been known since ancient times, one of only 11 elements people used before modern chemistry.