Problem 51 - Chemistry Structure and Dynamics

Question

In the first synthesis of an isotope of mendelevium \((Z=\) 101), Ghiorso and co-workers bombarded \({ }^{253}\) Es with \(\alpha\) particles. Starting with less than \(10^{-12}\) gram of einsteinium, they isolated one atom of mendelevium after a period of a few hours. If a neutron was emitted in this reaction, what isotope of Md was produced? Another isotope of mendelevium was produced by bombarding \({ }^{238} \mathrm{U}\) with \({ }^{19} \mathrm{~F}\) atoms. If five neutrons were ejected in this reaction, what isotope of Md was produced?

Step-by-Step Solution

Answer

The isotopes produced are \(^{256}\text{Md}\) and \(^{252}\text{Md}\).

Step 1: Understand the Reaction with Einsteinium

The isotope of einsteinium involved is \[ {}^{253} \text{Es} \] It is bombarded with alpha particles, which are essentially helium nuclei consisting of 2 protons and 2 neutrons: \[ {}^4_2 \text{He} \]A neutron is emitted during this process.

Step 2: Calculate the Resulting Isotope with Einsteinium

The nuclear reaction can be expressed as:\[ {}^{253}_{99} \text{Es} + {}^4_2 \text{He} \rightarrow {}^A_{101} \text{Md} + {}^1_0 \text{n} \]Adding the mass numbers (top numbers): \[ 253 + 4 = A + 1 \]Solving for \( A \):\[ A = 256 \]Thus, the isotope of mendelevium formed is \[ {}^{256} \text{Md} \]However, we need the atomic numbers (bottom numbers) to balance: \[ 99 + 2 = 101 \] which confirms the transmutation to Md.

Step 3: Understand the Reaction with Uranium

The isotope of uranium used is: \[ {}^{238}_{92} \text{U} \]It is bombarded with fluorine atoms:\[ {}^{19}_9 \text{F} \]Five neutrons are ejected in this process.

Step 4: Calculate the Resulting Isotope with Uranium

The nuclear reaction can be written as:\[ {}^{238}_{92} \text{U} + {}^{19}_9 \text{F} \rightarrow {}^B_{101} \text{Md} + 5\times{}^1_0 \text{n} \]For mass numbers:\[ 238 + 19 = B + 5 \257 = B + 5 \B = 252 \]So the isotope of mendelevium formed is:\[ {}^{252} \text{Md} \]For atomic numbers (bottom numbers):\[ 92 + 9 = 101 \]This confirms the atomic transmutation to Md.

Key Concepts

Isotope Production

Isotope production is a fascinating phenomenon in nuclear chemistry where scientists synthesize new isotopes using different methods. These isotopes often have unique properties that are valuable for research and application in different fields. In this context, a key technique utilized is nuclear bombardment.

Here, the desired isotope is created by bombarding a target atom with smaller particles. This process is instrumental in the careful synthesis of rare elements. For example, the isotope of mendelevium \(^{256} \text{Md}\) was produced during an experiment where einsteinium \(^{253} \text{Es}\) was bombarded with alpha particles. In another example, \(^{252} \text{Md}\) was synthesized by bombarding uranium \(^{238} \text{U}\) with fluorine atoms, showcasing how different combinations can lead to the production of various isotopes.

This controlled process of isotope production not only expands our understanding of the periodic table but also offers practical benefits, such as in medical applications and scientific research. Each carefully selected reaction and method of bombardment tailors the resulting isotopes to specific research needs and expands the boundaries of what was previously possible.

Alpha Particle Bombardment

Alpha particle bombardment involves the process of striking a target nucleus with alpha particles to induce nuclear reactions that can lead to the formation of new isotopes. Alpha particles are essentially helium nuclei, made up of 2 protons and 2 neutrons, symbolized as \(^4_2 \text{He}\).

In the experiment that produced mendelevium \(^{256} \text{Md}\), alpha particles collided with einsteinium \(^{253} \text{Es}\). As a result of this high-energy interaction, the target nucleus captured the alpha particle, and a neutron was emitted. This neutron emission is critical as it balances the reaction and leads to the transmutation of elements through the process.

The choice of alpha particles is significant because their relatively heavy mass (compared to other particles) can facilitate deeper penetration into the target nucleus, increasing the likelihood of a successful reaction. Alpha particle bombardment is a robust method in nuclear chemistry for synthesizing superheavy elements, thereby enriching our knowledge about the limits and formation of these rare elements.

Neutron Emission

Neutron emission is a crucial aspect of certain nuclear reactions during the bombardment processes. When a target nucleus absorbs a particle like an alpha particle, it may release one or more neutrons to maintain nuclear stability. This emission is essential in balancing mass numbers in nuclear equations.

During the synthesis of mendelevium isotopes, neutron emission played a vital role. For instance, in creating \(^{256} \text{Md}\), the reaction involved einsteinium \(^{253} \text{Es}\) being bombarded with alpha particles, resulting in the emission of one neutron. Similarly, in the synthesis of \(^{252} \text{Md}\), five neutrons were emitted after uranium \(^{238} \text{U}\) was bombarded with fluorine atoms.

Neutron emissions help in ensuring that the resulting isotopes are stable enough or provide the desired atomic structure needed for experimental or real-world applications. The role of neutron emission in balancing the mass number during these high-energy transformations can lead to the creation of isotopes with specific desired properties, highlighting the meticulous precision required in nuclear reactions.