Key PointsThe lanthanide and also actinide collection make up the inner change metals.The lanthanide collection includes elements 58 to 71, which to fill their 4f sublevel progressively.The actinides are elements 89 come 103 and also fill your 5f sublevel progressively.Actinides are common metals and have properties of both the d-block and the f-block elements, however they are additionally radioactive.Lanthanides have various chemistry from shift metals since their 4f orbitals are shielded native the atom’s environment.

You are watching: What periods are the lanthanides and actinides

Termslanthanide contractionThe gradual decrease in the radii of atom of the lanthanide facets as the atomic number increases; obvious in various physical properties of the elements and also their compounds.lanthanideAny the the 14 rarely earth elements from lanthanum come lutetium in the regular table. Due to the fact that their outermost orbitals are empty, they have actually very similar chemistry. Listed below them space the actinides.actinideAny that the 14 radioactive facets of the routine table that are positioned under the lanthanides, v which they share comparable chemistry.

The lanthanides and also actinides type a team that appears almost disconnected from the remainder of the regular table. This is the f block of elements, known as the inner transition series. This is as result of the proper numerical position between Groups 2 and also 3 that the transition metals.

A empty periodic table showing the lanthanide and also actinide seriesThe red highlighted group shows the lanthanide collection and the blue highlighted group shows the actinide series.

Electron Configuration

The 14 facets (numbers 58 come 71) the the lanthanide series are likewise known as the rare earth elements. Most lanthanides are formed when uranium and plutonium undergo nuclear reactions. Atom bombs charged through plutonium (actinoid) were provided in people War II. Plutonium was a power resource for Voyager spacecrafts released in 1977 and also is likewise used in artificial heart pacemakers.

The f sublevel consists of seven orbitals, each of which will hold two electrons. Therefore, it is feasible to ar 14 electrons in the 4f sublevel. Usually speaking, the lanthanides have actually electron configurations the follow the Aufbau rule, and the 4f sublevel is filled together atomic number boosts from cerium (Ce) to lutetium (Lu). However, there room three lanthanide metals that have actually properties similar to the d block: cerium (Ce), lutetium (Lu), and gadolinium (Gd). All of these steels contain a d electron in their electron configuration.

A comparable overall trend holds for the 14 aspects in the actinide series (numbers 90 to 103): native thorium (Th) to Lawrencium (Lr), the 5f sublevel is increasingly filled.

Elemental Properties

The chemistry of the lanthanides differs from key group elements and transition metals due to the fact that of the nature that the 4f orbitals. These orbitals room “buried” inside the atom and are shielded indigenous the atom’s environment by the 4d and also 5p electrons. As a consequence, the chemistry that the elements is largely established by your size, i m sorry decreases slowly with enhancing atomic number. This phenomenon is recognized as the lanthanide contraction. All the lanthanide aspects exhibit the oxidation state +3.

Actinides are usual metals. All of them are soft, have actually a silvery shade (but tarnish in air), and have relatively high density and also plasticity. Few of them deserve to be reduced with a knife. The hardness of thorium is comparable to the of soft steel, therefore heated pure thorium have the right to be rolling in sheets and pulled into wire. Thorium is nearly half as dense as uranium and plutonium however is harder than both of them.

Unlike the lanthanides, most elements of the actinide series have the exact same properties as the d block. Members the the actinide collection can lose multiple electrons to kind a variety of different ions. Every actinides are radioactive, paramagnetic, and, through the exception of actinium, have several crystalline phases. Every actinides are pyrophoric, particularly when carefully divided (i.e., they spontaneously ignite upon exposure come air).

See more: Can Mixtures Be Separated By Chemical Means, Separating Mixtures

The melting point of actinides walk not have a clear dependence on the variety of f electrons. The unusually short melting point of neptunium and plutonium (~640 °C) is defined by hybridization that 5f and 6d orbitals and the formation of directional binding in these metals. Prefer the lanthanides, every actinides are very reactive through halogens and chalcogens; however, the actinides react an ext easily. Actinides, specifically those v a small variety of 5f electrons, space prone come hybridization. This is defined by the similarity of the electron energies in ~ the 5f, 7s, and 6d subshells. Many actinides exhibition a larger range of valence states.

Boundless vets and curates high-quality, open licensed contents from roughly the Internet. This particular resource used the following sources: