Problem 7 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The atomic number of Unnilunium is

Step-by-Step Solution

Answer

The atomic number of Unnilunium (Mendelevium) is 101.

Step 1: Understanding Atomic Numbers

The atomic number of an element is defined as the number of protons in the nucleus of an atom. It is a unique identifier for each element on the periodic table.

Step 2: Identify Unnilunium

Unnilunium is the former name for the element Mendelevium, which was given the temporary IUPAC name until it was officially named. It belongs to the actinide series of the periodic table.

Step 3: Locate Mendelevium on the Periodic Table

Locate Mendelevium on the periodic table. Mendelevium, with the symbol Md, is positioned among the actinides and has a place on the periodic table.

Step 4: Determine Atomic Number

Find Mendelevium’s position on the periodic table to determine its atomic number, which is listed as 101.

Key Concepts

Periodic Table

The periodic table is an organized chart of chemical elements arranged by increasing atomic number, which is the number of protons in an atom's nucleus. Each horizontal row on the table is called a period, and each vertical column is called a group.

Elements in the same group usually share similar properties and chemical behaviors, because they have the same number of valence electrons. For instance, all elements in the first group, known as alkali metals, are highly reactive with water.

• Metals are generally found on the left and in the center of the table,
• Non-metals are on the right,
• Metalloids, which have properties of both, border the stair-step line between metals and non-metals.

The table not only helps scientists understand element properties but also aids in predicting the behavior and reactions of yet-to-be-discovered elements.

Mendelevium

Mendelevium is a synthetic element with the symbol Md and atomic number 101. It was named after Dmitri Mendeleev, the founder of the periodic table, and is a part of the actinide series. The discovery of Mendelevium occurred in 1955, when it was first synthesized at the University of California, Berkeley, by bombarding einsteinium with alpha particles. Being a man-made element, Mendelevium is not found naturally in the environment and can only be produced in small amounts in laboratories.

It is known for its radioactive properties, with all its isotopes being unstable. The most stable isotope, Md-258, has a half-life of just 51.5 days. This means it decays into another form within a relatively short period.

• Mendelevium does not have significant commercial applications due to its scarcity and radioactivity,
• Its primary use is in scientific research,
• It helps scientists study nuclear reactions and the properties of heavy elements.

Actinide Series

The Actinide series is a group of 15 metallic elements with atomic numbers from 89 (actinium) to 103 (lawrencium) on the periodic table. These elements are all part of the block known as the f-block, characterized by their filling of the 5f electron orbital. Actinides are typically radioactive and have high atomic numbers. Many of them, including uranium and thorium, are well-known for their roles in nuclear reactions and energy production.

Here are some noteworthy features of the actinide series:

• They have similar properties, such as being highly electropositive and reactive metals, often tarnishing when exposed to air.
• The majority of actinides are synthetic and were identified in laboratories.
• Elements like plutonium and neptunium have key significance in nuclear technology.

Due to their radioactivity, special precautions are required when handling actinides. They continue to be a significant area of study in chemistry, physics, and materials science due to their complex structures and fascinating chemical behaviors.