Actinium (Ac) – Periodic Table (Element Information & More)

This is a SUPER easy guide on Actinium element.

In fact, the table mentioned below is the perfect information box (Which gives you every single detail about the Actinium element in Periodic table.)

So if you want to know anything about Actinium element, then this guide is for you.

Let’s finish this very quickly.

Actinium Element (Ac) Information

Appearance	Silvery white appearance
State (at STP)	Solid
Position in Periodic table	Group: actinides, Period: 7, Block: d
Category	Actinides
Atomic number or  Protons	89
Neutrons	138
Electrons	89
Symbol	Ac
Atomic mass of Actinium (most stable isotope)	227 u
Electrons arrangement or  Bohr model	2, 8, 18, 32, 18, 9, 2
Electronic configuration	[Rn] 6d1 7s2
Atomic radius	260 picometers (van der Waals radius)
1st Ionization energy	5.17 eV
Electronegativity	1.1 (Pauling scale)
Crystal structure	FCC (face centered cubic)
Density	10.07 g/cm3
Main isotope	227Ac
Who discovered Actinium and when?	Friedrich Oskar Giesel (in 1902)
CAS number	7440-34-8

Actinium in Periodic table

Actinium element is in period 7 of the Periodic table. Actinium is the d-block element and it belongs to actinides group.

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Why is Actinium in Period 7?

Let me ask you a question.

How many shells does actinium have?

It’s 7. Right? 

You have already seen the bohr model of actinium atom in the above table.

From the Bohr model, it can be found that the number of orbits or shells in actinium is 7. Hence, as actinium has 7 orbits, it lies in period 7 of the Periodic table. 

Why is Actinium in d-block?

Before knowing this reason, first of all I want to ask you a simple question.

How can you determine the blocks-wise position of elements?

The simple answer: The elements will lie in the s, p, d or f block will completely depend upon the subshell in which the last electron will enter.

For example; the electron configuration of actinium is [Rn] 7s² 6d¹.

So the last electron of actinium enters the d-subshell or d-orbital. 

Hence, actinium is the d-block element.

5 Interesting facts about Actinium

Interesting facts about actinium element are mentioned below.

1. The word actinium was derived from the Greek word “aktis”, which means beam.
2. Actinium was discovered by Friedrich Oskar Giesel in 1902.
3. Actinium has many isotopes and all those isotopes are radioactive.
4. Actinium naturally occurs in uranium ore.
5. Actinium is around 150 times more radioactive than radium element.

Properties of Actinium

The physical and chemical properties of actinium element are mentioned below.

Physical properties of Actinium

Physical properties of actinium are mentioned below.

• Actinium is a radioactive element having a silvery white appearance.
• In a dark room, actinium glows blue in color.
• The atomic mass of the most stable isotope of actinium is 227 u and its density is 10.07 g/cm³.
• The crystal structure of Actinium is FCC (i.e face centered cubic).

Chemical properties of Actinium

Chemical properties of actinium are mentioned below.

• In the moist air, actinium reacts with oxygen and forms a thin coating of actinium oxide on it.
• Actinium is a radioactive element and it is hazardous to human health due to its radioactivity.
• If actinium enters the human body, then it will get deposited into bones and lever, which damages the cells due to radioactive decay. This causes bone cancer and other illnesses.
• The most common oxidation state of actinium is +3.

Uses of Actinium

Actinium is generally used for research work. But apart from this, actinium is also a good source of neutrons. It can also be used in treatment of cancer.

Moreover due to its radioactive nature, it is not commercially used.

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External resources:

1. Actinium – Element information, properties and uses | Periodic Table. (n.d.). Actinium – Element Information, Properties and Uses | Periodic Table. https://www.rsc.org/periodic-table/element/89/actinium
2. Actinium – Wikipedia. (2011, June 2). Actinium – Wikipedia. https://en.wikipedia.org/wiki/Actinium
3. P. (n.d.). Actinium | Ac (Element) – PubChem. Actinium | Ac (Element) – PubChem. https://pubchem.ncbi.nlm.nih.gov/element/Actinium
4. It’s Elemental – The Element Actinium. (n.d.). It’s Elemental – the Element Actinium. https://education.jlab.org/itselemental/ele089.html
5. C&EN: IT’S ELEMENTAL: THE PERIODIC TABLE – ACTINIUM. (n.d.). C&EN: IT’S ELEMENTAL: THE PERIODIC TABLE – ACTINIUM. http://pubsapp.acs.org/cen/80th/actinium.html?