Problem 26 - Chemistry and Chemical Reactivity

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?

Step-by-Step Solution

Answer

Seventh period has 32 elements, mostly actinides, characterized by radioactivity.

Step 1: Understand the Question

The question is asking for the number of elements that are part of the seventh period in the periodic table, along with the common group name of these elements, and a characteristic property that many of them share.

Step 2: Identify the Seventh Period

The periodic table is organized into periods (horizontal rows) and groups (vertical columns). The seventh period is the last row of the current periodic table.

Step 3: Count the Elements

The seventh period contains 32 elements, ranging from Francium (atomic number 87) to Oganesson (atomic number 118).

Step 4: Determine the Group Name

Most elements in the seventh period are known as 'actinides', which are found in the f-block of the periodic table. However, beyond the actinides, this period also has transition metals and p-block elements.

Step 5: Identify Characteristic Property

A well-known property of the actinides, which form a significant part of the seventh period, is their radioactive nature, where they exhibit radioactivity.

Key Concepts

Periodic Table

The Periodic Table is a comprehensive chart that organizes all known chemical elements based on their atomic number, electron configurations, and recurring chemical properties. This arrangement allows us to discern trends and make predictions about element behavior with minimal effort. The table is structured into rows known as periods and columns called groups. Each period corresponds to the highest energy level that electrons occupy for the elements within that row.

In total, there are seven periods in the modern periodic table. The seventh period is unique because it includes a mix of different element types. It consists of 32 elements, more than any other period, ranging from Francium (Fr) to Oganesson (Og). These elements, by virtue of their placement, reflect completions or ongoing processes within their electron configurations, giving them unique characteristics that are often understood through the lens of their specific periods and groups.

Actinides

Actinides are a series of elements found between atomic numbers 89 (Actinium) and 103 (Lawrencium). They take their name from Actinium, the first element in the series. Most actinides are located in the f-block of the periodic table, distinctly separated from the other elements in what's often referred to as a bottom "island" on the periodic chart.

These elements are notable for a couple of reasons:

• They tend to have large atomic and ionic radii.
• They often have several oxidation states, which makes them versatile in chemical reactions.

Many of the actinides are "transuranic," meaning they occur after Uranium (atomic number 92) in the periodic table.
Despite these interesting attributes, the feature that stands out the most for the actinides is their radioactivity. This intrinsic property is due to the instability of their nucleus, which results in the emission of radiation as they transition to more stable forms.

Radioactivity

Radioactivity is a fascinating yet complex property exhibited by several elements, primarily the actinides, in the seventh period of the periodic table. It involves the emission of particles or electromagnetic waves due to the unstable nuclei of certain atoms. This instability leads to the spontaneous breakdown of the nucleus, a process that emits energy in the form of radiation.

There are three common types of radioactive emissions:

• Alpha particles, which are heavy and positively charged.
• Beta particles, which are lighter and can be either positively or negatively charged.
• Gamma rays, which are high-energy electromagnetic waves.

The phenomena of radioactivity are crucial both in nature and in various technological applications. It plays a significant role in fields ranging from energy production to medical treatments. Furthermore, understanding radioactivity provides insights into the decay rates and half-lives of elements, which are essential in calculating the age of objects and understanding geological time scales.