Properties Of Lanthanides And Actinides

The lanthanides and actinides form a group that appears almost disconnected from the rest of the periodic table. This is the f block of elements, known as the inner transition series. This is due to the proper numerical position between Groups 2 and iii of the transition metals.

A blank periodic tabular array showing the lanthanide and actinide series

The red highlighted group shows the lanthanide series and the blueish highlighted group shows the actinide serial.

Electron Configuration

The fourteen elements (numbers 58 to 71) of the lanthanide series are also known as the rare earth elements. Near lanthanides are formed when uranium and plutonium undergo nuclear reactions. Atomic bombs charged with plutonium (actinoid) were used in World War Two. Plutonium was a power source for Voyager spacecrafts launched in 1977 and is also used in bogus eye pacemakers.

The f sublevel contains seven orbitals, each of which will hold two electrons. Therefore, it is possible to identify 14 electrons in the 4f sublevel. By and large speaking, the lanthanides have electron configurations that follow the Aufbau rule, and the 4f sublevel is filled every bit atomic number increases from cerium (Ce) to lutetium (Lu). However, at that place are iii lanthanide metals that have backdrop similar to the d block: cerium (Ce), lutetium (Lu), and gadolinium (Gd). All of these metals contain a d electron in their electron configuration.

A like overall tendency holds for the 14 elements in the actinide series (numbers 90 to 103): from thorium (Thursday) to Lawrencium (Lr), the 5f sublevel is progressively filled.

Elemental Properties

The chemical science of the lanthanides differs from principal group elements and transition metals because of the nature of the 4f orbitals. These orbitals are "cached" within the cantlet and are shielded from the cantlet's environment by the 4d and 5p electrons. As a consequence, the chemistry of the elements is largely determined by their size, which decreases gradually with increasing diminutive number. This phenomenon is known as the lanthanide contraction. All the lanthanide elements exhibit the oxidation state +three.

Actinides are typical metals. All of them are soft, take a silvery colour (but tarnish in air), and take relatively high density and plasticity. Some of them can be cutting with a knife. The hardness of thorium is like to that of soft steel, and then heated pure thorium can exist rolled in sheets and pulled into wire. Thorium is almost half equally dense as uranium and plutonium but is harder than both of them.

Unlike the lanthanides, most elements of the actinide series have the same properties as the d block. Members of the actinide series can lose multiple electrons to grade a variety of different ions. All actinides are radioactive, paramagnetic, and, with the exception of actinium, take several crystalline phases. All actinides are pyrophoric, specially when finely divided (i.e., they spontaneously ignite upon exposure to air).

The melting point of actinides does non take a clear dependence on the number of f electrons. The unusually depression melting point of neptunium and plutonium (~640 °C) is explained by hybridization of 5f and 6d orbitals and the formation of directional bonds in these metals. Similar the lanthanides, all actinides are highly reactive with halogens and chalcogens; notwithstanding, the actinides react more easily. Actinides, especially those with a minor number of 5f electrons, are decumbent to hybridization. This is explained by the similarity of the electron energies at the 5f, 7s, and 6d subshells. Near actinides exhibit a larger variety of valence states.