Thorium (Th)

Thorium properties

Atomic number

90

Atomic mass

232.04 u

Category

Actinide

Group

—

Period

7

Block

f-block

State at room temp.

Solid

Electronegativity

1.3

Melting point

2,023 K (1,749.8 °C)

Boiling point

5,061 K (4,787.8 °C)

Density

11.72 g/cm³

Valence electrons

2

Common charges

+4

Oxidation states

+4

Atomic radius

237 pm

Ionization energy

6.08 eV

Electron affinity

—

Radioactive

Yes, no stable isotopes

Discovered

1829

Thorium electron configuration

The electron configuration of Thorium (Th) is [Rn] 6d2 7s2. Its 90 electrons are arranged in shells as 2, 8, 18, 32, 18, 10, 2.

Protons, neutrons and electrons in Thorium

A neutral Thorium atom has 90 protons and 90 electrons. Most Thorium atoms have about 142 neutrons: the atomic mass rounded to 232, minus the atomic number 90.

Neutrons are approximate: atoms of the same element can have different numbers of neutrons (isotopes). Atomic number and mass

How many valence electrons does Thorium have?

2

Thorium has 2 valence electrons in its outermost shell. As an f-block element, its 4f or 5f electrons can also take part in bonding.

See every element: Periodic table with valence electrons

Thorium orbital diagram

Each box is an orbital that holds up to two electrons with opposite spins (↑↓). The inner shells are the same as the noble gas in brackets. How to write electron configurations

Molar mass of Thorium

232.04 g/mol

One mole of Thorium atoms (6.022 × 10²³ atoms) has a mass of 232.04 grams. Use this value to convert between grams and moles.

Thorium facts

• Thorium is roughly three times as abundant in Earth's crust as uranium.
• Its main natural isotope, thorium-232, has a half-life of about 14 billion years, roughly the age of the universe.
• Thorium (Th) has atomic number 90 and is a solid at room temperature. It was discovered in 1829.

Position in the periodic table

Thorium is element 90, in period 7 of the periodic table. It is one of the Actinides in the f-block, shown in the rows below the main table.

All actinides

Uses of Thorium

Thorium dioxide has one of the highest melting points of any oxide, so it was long used in gas lantern mantles, which glow brightly when heated, and is still added to some tungsten welding electrodes. Thorium is also studied as a nuclear fuel: thorium-232 absorbs neutrons and turns into uranium-233, which can sustain a chain reaction. India is developing reactors to use its large thorium reserves.

Who discovered Thorium?

Swedish chemist Jöns Jacob Berzelius identified thorium in 1829 in a black mineral from a Norwegian island, now called thorite. He named it after Thor, the Norse god of thunder.

Where does the name come from?

Thorium is named after Thor, the Norse god of thunder. Jöns Jacob Berzelius chose the name in 1829 when he discovered the element in a black mineral from Norway, later named thorite.

Discovery timeline