Transition metalElement 43 · d-block

Technetium (Tc)

Technetium (Tc) is a transition metal with atomic number 43; its most stable known isotope has mass number 97. At room temperature it is a solid that melts at 2,157 °C and boils at 4,262 °C.

43TcTechnetium[97]

Atomic number

protons

Atomic weight

[97]

most stable isotope

Melting point

2,157 °C

2,430.15 K

Boiling point

4,262 °C

4,535.15 K

Density

11 g/cm³

near room temperature

Electronegativity

1.9

Pauling scale

State at 25 °C

Solid

Discovered

1937

Italy

Technetium at a glance

Identity

Symbol	Tc
Atomic number (Z)	43
Atomic weight	[97] mass number of the most stable isotope
Category	Transition metal
Group	7
Period	5
Block	d-block
CAS number	7440-26-8

Atomic properties

Electron configuration	[Kr] 4d⁵ 5s² Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d⁵ 5s²
Electrons per shell	2, 8, 18, 13, 2
Oxidation states	+4, +7 Less common: -3, -1, +1, +2, +3, +5, +6
Electronegativity (Pauling)	1.9
First ionisation energy	7.119 eV (686.9 kJ/mol) 2nd: 15.26 eV · 3rd: 29.55 eV
Electron affinity	0.55 eV
Atomic radius (empirical)	135 pm
Covalent radius	128 pm
Van der Waals radius	216 pm

Physical properties

State at 25 °C	Solid
Melting point	2,157 °C · 3,914.6 °F · 2,430.15 K
Boiling point	4,262 °C · 7,703.6 °F · 4,535.15 K
Density	11 g/cm³
Thermal conductivity	50.6 W/(m·K)
Crystal structure	Hexagonal

Isotopes & abundance

Natural occurrence	Trace in nature / mostly synthetic
Radioactive	Yes
Stable isotopes	3
Most stable isotope	⁹⁷Tc — half-life 4.21 million years
Known isotopes	40

Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.

Technetium electron configuration

Technetium has 43 electrons. Written in short form, its ground-state configuration is [Kr] 4d⁵ 5s² — the electrons of the noble gas krypton, plus 4d⁵ 5s².Written out in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d⁵ 5s².

4d↑↑↑↑↑

5s↑↓

Discovery and name

Discovered

1937 — Carlo Perrier and Emilio Segrè · Italy.

Name

Greek tekhnētos, artificial — the first element made artificially.

Known for

The lightest element with no stable isotopes. Technetium-99m is the most widely used medical radioisotope, in tens of millions of scans a year.

Isotopes of technetium

Technetium has no stable isotopes and does not occur naturally in significant amounts. Its longest-lived known isotope is:

Isotope	Protons	Neutrons	Half-life
⁹⁷Tc	43	54	4.21 million years

40 isotopes of technetium are known in our data set (half-lives as published in nuclear data tables).

Technetium compared with group 7

The other elements in group 7, from top to bottom of the table:

Element	Z	Atomic weight	Melting point	Boiling point	Density	Electronegativity
Manganese	25	54.938	1,246 °C	2,061 °C	7.3 g/cm³	1.55
Technetium	43	[97]	2,157 °C	4,262 °C	11 g/cm³	1.9
Rhenium	75	186.21	3,185 °C	5,590 °C	20.8 g/cm³	1.9
Bohrium	107	[270]	—	—	37.1 g/cm³ (pred.)	—

Frequently asked questions

6 answers

What is the atomic mass of technetium?

Technetium has no stable isotopes, so it has no standard atomic weight. Periodic tables show [97], the mass number of its most stable known isotope.

How many protons, neutrons and electrons does technetium have?

A neutral technetium atom has 43 protons and 43 electrons. Its most stable isotope, technetium-97, has 54 neutrons.

What is the electron configuration of technetium?

[Kr] 4d⁵ 5s² (in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d⁵ 5s²).

What are the melting and boiling points of technetium?

Technetium melts at 2,157 °C (3,914.6 °F) and boils at 4,262 °C (7,703.6 °F).

Is technetium a metal?

Technetium is a metal. It is in group 7, period 5, and is a solid at room temperature.

Who discovered technetium?

1937 — Carlo Perrier and Emilio Segrè (Italy).