Nickel at a glance
- Atomic number
- 28
- Symbol
- Ni
- Atomic mass
- 58.693 u
- Category
- Transition metal
- Group / period
- 10 / 4
- Electron configuration
- [Ar] 3d 8 4s 2
- State at 25 °C
- Solid
- Melting point
- 1455 °C
- Boiling point
- 2913 °C
- Density
- 8.912 g/cm³
- Electronegativity
- 1.91
- 1st ionization energy
- 737 kJ/mol
- Oxidation states
- +2
- Discovered
- 1751
Atomic structure
A neutral nickel atom has 28 protons and 28 electrons, and its most common isotope carries about 30 neutrons. One atom weighs about 9.75 × 10⁻²⁶ kg, so a mole of nickel (6.022 × 10²³ atoms) weighs 58.693 g. That nucleus holds 1.07 neutrons for every proton. The electrons fill 4 shells (K 2, L 8, M 16, N 2), which gives the configuration [Ar] 3d 8 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: Ni-58, Ni-60, Ni-61, Ni-62 and Ni-64. Its most common isotope, Ni-58, has the same mass number as Fe-58: isobars, nuclei of different elements with 58 nucleons each.
Physical properties
At room temperature (25 °C) nickel is a solid. It melts at 1455 °C and boils at 2913 °C, so it stays liquid across a 1458-degree range. It stays solid in a candle flame (about 1000 °C) but would melt in molten iron (1538 °C). Its density is 8.912 g/cm³, 8.91 times as dense as water. Its atoms have a radius of about 135 pm (Cobalt next door is 135 pm). In the solid, its atoms pack into a face-centred cubic lattice.
Chemical behaviour
Its electronegativity is 1.91 on the Pauling scale. Pulling off its outermost electron takes 737 kJ/mol. A bond between nickel and chlorine would be polar covalent, with an electronegativity difference of 1.3. It releases 112 kJ/mol when it gains an extra electron. Its common oxidation states are +2, so in compounds you will usually meet it as Ni²⁺. Group 10 also holds Palladium, Platinum and Darmstadtium, which share its outer-shell pattern.
Where it comes from
It makes up 84 mg/kg of Earth's crust, the 23rd most abundant element there. It was first identified in 1751, making it the 17th element to be discovered (counting the 11 known since antiquity together).