Actinium (Ac)
Actinium gave its name to the actinide series, the row of 15 elements from actinium to lawrencium.
Actinium properties
- Atomic mass
- 227 u
- Category
- Actinide
- Group
- —
- Period
- 7
- Block
- f-block
- State at room temp.
- Solid
- Melting point
- 1,323 K (1,049.8 °C)
- Boiling point
- 3,471 K (3,197.8 °C)
- Density
- 10.07 g/cm³
- Atomic radius
- 260 pm
- Ionization energy
- 5.17 eV
- Electron affinity
- —
- Radioactive
- Yes, no stable isotopes
- Discovered
- 1899
Actinium electron configuration
- Electron configuration
- [Rn] 6d1 7s2
- Full electron configuration
- 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6 6d1 7s2
- Electron shells
- 2 · 8 · 18 · 32 · 18 · 9 · 2
The electron configuration of Actinium (Ac) is [Rn] 6d1 7s2. Its 89 electrons are arranged in shells as 2, 8, 18, 32, 18, 9, 2.
Protons, neutrons and electrons in Actinium
A neutral Actinium atom has 89 protons and 89 electrons. Most Actinium atoms have about 138 neutrons: the atomic mass rounded to 227, minus the atomic number 89.
Neutrons are approximate: atoms of the same element can have different numbers of neutrons (isotopes). Atomic number and mass
How many valence electrons does Actinium have?
2
Actinium has 2 valence electrons in its outermost shell. As an f-block element, its 4f or 5f electrons can also take part in bonding.
Actinium 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 Actinium
227 g/mol
One mole of Actinium atoms (6.022 × 10²³ atoms) has a mass of 227 grams. Use this value to convert between grams and moles.
Actinium facts
- Actinium gave its name to the actinide series, the row of 15 elements from actinium to lawrencium.
- Actinium glows with a pale blue light in the dark because its intense radioactivity excites the surrounding air.
- Actinium (Ac) has atomic number 89 and is a solid at room temperature. It was discovered in 1899.
Position in the periodic table
Actinium is element 89, 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.
Uses of Actinium
Actinium is too rare and radioactive for everyday uses. Actinium-227 mixed with beryllium has been used as a neutron source, and actinium-225 is being developed for targeted alpha therapy, in which it is attached to molecules that carry it directly to cancer cells. Because it is so scarce in nature, actinium for research is made artificially, for example by bombarding radium with neutrons.
Who discovered Actinium?
French chemist André-Louis Debierne discovered actinium in Paris in 1899 in pitchblende residues left after the Curies extracted radium, and Friedrich Oskar Giesel found it independently in 1902. Its name comes from the Greek aktis, meaning 'ray' or 'beam'.
Where does the name come from?
Actinium comes from the Greek aktis (genitive aktinos), meaning 'ray' or 'beam'. André-Louis Debierne named it in 1899 for its radioactivity, the rays given off as its atoms decay.
Actinide
Compare Actinium
FAQ
What is the electron configuration of Actinium?
The electron configuration of Actinium (Ac) is [Rn] 6d1 7s2. Its 89 electrons are arranged in shells as 2, 8, 18, 32, 18, 9, 2.
How many protons, neutrons and electrons does Actinium have?
A neutral Actinium atom has 89 protons and 89 electrons. Most Actinium atoms have about 138 neutrons: the atomic mass rounded to 227, minus the atomic number 89.
How many valence electrons does Actinium have?
Actinium has 2 valence electrons in its outermost shell. As an f-block element, its 4f or 5f electrons can also take part in bonding.
What is the molar mass of Actinium?
The molar mass of Actinium is 227 g/mol. This is the same number as its atomic mass, 227 u.
Is Actinium a metal?
Yes. Actinium is an actinide, so it is a metal.
Is Actinium radioactive?
Yes. Actinium has no stable isotopes, so all of its atoms are radioactive and eventually decay into other elements.
Where is Actinium on the periodic table?
Actinium is element 89, 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.