Zinc at a glance
- Atomic number
- 30
- Symbol
- Zn
- Atomic mass
- 65.38 u
- Category
- Transition metal
- Group / period
- 12 / 4
- Electron configuration
- [Ar] 3d 10 4s 2
- State at 25 °C
- Solid
- Melting point
- 419.5 °C
- Boiling point
- 906.9 °C
- Density
- 7.134 g/cm³
- Electronegativity
- 1.65
- 1st ionization energy
- 906 kJ/mol
- Oxidation states
- +2
- Discovered
- 1746
Atomic structure
A neutral zinc atom has 30 protons and 30 electrons, and its most common isotope carries about 34 neutrons. One atom weighs about 1.09 × 10⁻²⁵ kg, so a mole of zinc (6.022 × 10²³ atoms) weighs 65.38 g. That nucleus holds 1.13 neutrons for every proton. The electrons fill 4 shells (K 2, L 8, M 18, N 2), which gives the configuration [Ar] 3d 10 4s 2. As a d-block element, both its outer s electrons and its inner d electrons can take part in bonding, which is why it shows more than one oxidation state. It has 5 stable isotopes: Zn-64, Zn-66, Zn-67, Zn-68 and Zn-70. Its most common isotope, Zn-64, has the same mass number as Ni-64: isobars, nuclei of different elements with 64 nucleons each.
Physical properties
At room temperature (25 °C) zinc is a solid. It melts at 419.5 °C and boils at 906.9 °C, so it stays liquid across a 487.3-degree range. It stays solid in a hot kitchen oven but would melt in a candle flame (about 1000 °C). Its density is 7.134 g/cm³, 7.13 times as dense as water. Its atoms have a radius of about 135 pm (Copper next door is 135 pm). In the solid, its atoms pack into a hexagonal close-packed lattice.
Chemical behaviour
Its electronegativity is 1.65 on the Pauling scale. Pulling off its outermost electron takes 906 kJ/mol. A bond between zinc and chlorine would be polar covalent, with an electronegativity difference of 1.5. Its common oxidation states are +2, so in compounds you will usually meet it as Zn²⁺. Group 12 also holds Cadmium, Mercury and Copernicium, which share its outer-shell pattern.
Where it comes from
It makes up 70 mg/kg of Earth's crust, the 24th most abundant element there. In the human body it accounts for about 0.0032 % of body mass. It was first identified in 1746, making it the 16th element to be discovered (counting the 11 known since antiquity together). When excited it glows at its own set of colours; its brightest visible lines are at 481.1 nm, 636.2 nm and 472.2 nm. In a flame test its compounds colour the flame pale blue-green.