Lawrencium (Lr)
Element 103 · Actinide · Solid at 25 °C · Period 7 (f-block)
Lawrencium closes the actinide series and honors Ernest Lawrence, inventor of the cyclotron particle accelerator.
On the periodic table, lawrencium sits in the f-block in period 7. It is one of 15 elements classified as an actinide, and at room temperature (25 °C) it is a solid.
The actinides fill the 5f orbitals in the bottom row of the table, and every one of them is radioactive. Only thorium and uranium occur on Earth in significant quantities; the rest are made in reactors or particle accelerators. Their nuclear properties — fission above all — shaped the twentieth century.
Properties of lawrencium
| Atomic number (Z) | 103 |
|---|---|
| Symbol | Lr |
| Atomic mass | (262) (mass number of the most stable isotope; this element has no standard atomic weight) |
| Category | Actinide |
| Group | — (f-block, associated with group 3) |
| Period | 7 |
| Block | f-block |
| Metal / nonmetal | Metal |
| State at 25 °C | Solid |
| Electron configuration | [Rn] 5f14 7s2 7p1 |
| Electronegativity (Pauling) | — |
| Melting point | 1,627 °C (1,900.15 K / 2,960.6 °F) |
| Boiling point | — |
| Density | — |
Position in the periodic table
Lawrencium belongs to the actinides, the detached f-block row shown beneath the main table. These elements all fit between groups 2 and 4 of period 7, and are pulled out into their own row only to keep the table a manageable width.
Physical properties
Lawrencium has no accepted Pauling electronegativity value, which is why that field shows a dash.
Data notes
The atomic mass is shown in parentheses because this element has no standard atomic weight; the number given is the mass number of its most stable known isotope.
The state and electron configuration listed for this element are predicted values — it has never been produced in quantities large enough to observe directly.
See also: the interactive periodic table, how to read the periodic table, periodic trends.