Question

How many elements occur in the seventh period? What is the name given to the majority of these elements, and what well-known property characterizes them?

Short answer

The seventh period has 32 elements, mainly called actinides, characterized by radioactivity.

Step-by-step solution

Identify the Seventh Period

The periodic table is divided into periods. The seventh period is the final row on the modern periodic table, starting from francium (Fr, atomic number 87) and ending with oganesson (Og, atomic number 118).

Count the Number of Elements in the Period

To determine how many elements occur in the seventh period, count the atomic numbers from 87 to 118 for a total of 32 elements. Thus, the seventh period contains 32 elements.

Determine the Name of the Majority Elements

The majority of the elements in the seventh period are known as the 'actinides' and 'transactinides'. However, more specifically, 14 of them belong to a group called 'actinides', which dominate the period after the initial alkali and alkaline earth metals.

Identify the Characteristic Property of These Elements

A well-known characteristic property of the actinides, which are predominant in the seventh period, is their radioactivity. Many of these elements are also synthetic and not found naturally on Earth.

Key concepts

Actinides

The actinides are a series of elements found in the seventh period of the periodic table, and they span from thorium (Th, atomic number 90) to lawrencium (Lr, atomic number 103). These elements share similar properties due to their similar electron configurations. They're known for being highly radioactive and are often utilized in nuclear technology.

Most of the actinides are synthetic, which means they are not typically found in nature but can be created in laboratories. The first few elements in the actinide series, like uranium and thorium, are naturally occurring and are significant for their applications in nuclear energy and weapons.

- They have a silvery appearance but tarnish readily in air. - Chemically, actinides tend to form stable complexes with various ligands. - Actinides can exist in multiple oxidation states, which allows them to participate in a wide variety of chemical reactions.

Transactinides

Transactinides are the elements that come after actinium on the periodic table. These elements, which include those with atomic numbers from 104 to 118, are unique because they are all synthetic and have very short half-lives, making them extremely radioactive.

Due to their position in the periodic table, transactinides are part of the d-block and are considered transition metals, although they often exhibit properties that are quite different from lighter transition metals. Studies of transactinides help scientists understand better the effects of relativistic physics, which play a crucial role in the chemistry of these heavy elements.

- Experiments with transactinides require sophisticated technology due to their instability. - They are important for understanding the nuclear decay processes. - They have unique chemical properties that challenge existing theories about periodicity and element classification.

Radioactivity

Radioactivity is a fundamental characteristic property of many elements in the seventh period, especially amongst the actinides and transactinides. It refers to the process by which unstable atomic nuclei lose energy by emitting radiation. This radiation can take the form of alpha particles, beta particles, or gamma rays.

The radioactivity of these elements is due to their heavy nuclei, which are not stable; they are constantly trying to achieve a more stable state. This trait makes elements like uranium and plutonium very useful in generating nuclear power but also poses significant challenges for safe handling and disposal.

- Radioactive decay can lead to changes in an element's identity, changing it into a different element altogether. - Understanding radioactivity is vital for applications in medicine, energy production, and scientific research. - While radioactivity can be dangerous, it's also crucial for many modern technologies.