Cobalt (Co)
Element 27 · Transition metal · Solid at 25 °C · Group 9, Period 4
Cobalt has colored glass and ceramics deep blue for centuries; today it is critical in rechargeable batteries, jet-engine superalloys, and vitamin B12.
On the periodic table, cobalt sits in group 9 in period 4. It is one of 38 elements classified as a transition metal, and at room temperature (25 °C) it is a solid.
Transition metals occupy the wide d-block in the middle of the table. As a family they are hard, dense, high-melting metals that conduct heat and electricity well. Their partly filled d-orbitals let many of them take several oxidation states, form vividly colored compounds, and act as catalysts — which is why so much of industry, and so much of biology, runs on this block.
Properties of cobalt
| Atomic number (Z) | 27 |
|---|---|
| Symbol | Co |
| Atomic mass | 58.933 |
| Category | Transition metal |
| Group | 9 |
| Period | 4 |
| Block | d-block |
| Metal / nonmetal | Metal |
| State at 25 °C | Solid |
| Electron configuration | [Ar] 3d7 4s2 |
| Electronegativity (Pauling) | 1.88 |
| Melting point | 1,495 °C (1,768.15 K / 2,723 °F) |
| Boiling point | 2,927 °C (3,200.15 K / 5,300.6 °F) |
| Density | 8.9 g/cm³ |
Position in the periodic table
Cobalt shares group 9 with Rhodium (Rh), Iridium (Ir), Meitnerium (Mt). Elements in the same group have the same number of outer electrons, so they tend to behave alike chemically — comparing them is one of the fastest ways to see periodic trends in action.
Physical properties
Cobalt melts at 1,495 °C (1,768.15 K / 2,723 °F) and boils at 2,927 °C (3,200.15 K / 5,300.6 °F), giving it a liquid range of about 1,432 °C at standard pressure.
Its density is 8.9 g/cm³.
See also: the interactive periodic table, how to read the periodic table, periodic trends.