Problem 77 - Chemistry The Molecular Science

Question

Element 118 was first synthesized by collision of calcium- 48 nuclei with californium-249 nuclei. Three neutrons were emitted for each 118 nucleus formed. (a) Write a balanced nuclear equation to represent this process. (b) The element 118 nucleus underwent three successive alpha particle emissions. Write a series of balanced nuclear equations to represent this sequence. (c) Identify the group of the periodic table to which element 118 belongs. (d) What name is commonly used for that group?

Step-by-Step Solution

Answer

(a) \( ^{48}_{20}\text{Ca} + ^{249}_{98}\text{Cf} \rightarrow ^{294}_{118}\text{Og} + 3^1_0 \text{n} \); (b) \( \alpha \)-decay to \( ^{282}_{112}\text{Cn} \); (c) Group 18; (d) Noble Gases.

Step 1: Writing the Balanced Equation for Part (a)

To determine the balanced nuclear equation for the synthesis of element 118, begin with the known reactants: calcium and californium. The reaction is \( ^{48}_{20}\text{Ca} + ^{249}_{98}\text{Cf} \rightarrow ^{118}_{118}\text{Og} + 3^1_0 \text{n} \). The original atomic numbers and mass numbers must balance on both sides: \( 20 + 98 = 118 \) and \( 48 + 249 = 295 \) which balances with \( 118 + 3 \cdot 1 \). Thus, the balanced equation is correct.

Step 2: Writing the Series of Equations for Part (b)

Element 118, known as oganesson, undergoes alpha decay. The process can be divided into three stages, each resulting in the emission of an \( \alpha \) particle (an \( ^4_2 \text{He} \) nucleus).1. \( ^{294}_{118}\text{Og} \rightarrow ^{290}_{116}\text{Lv} + ^4_2\text{He} \)2. \( ^{290}_{116}\text{Lv} \rightarrow ^{286}_{114}\text{Fl} + ^4_2\text{He} \)3. \( ^{286}_{114}\text{Fl} \rightarrow ^{282}_{112}\text{Cn} + ^4_2\text{He} \).Each equation represents the emission of one \( \alpha \) particle reducing both the atomic and mass number.

Step 3: Identifying Element 118's Group for Part (c)

Element 118, oganesson, is part of group 18 in the periodic table. Group 18 is known for housing the noble gases, elements possessing full electron shells that characterize their stability and low reactivity.

Step 4: Naming the Group for Part (d)

Group 18 of the periodic table is commonly referred to as the "noble gases." This name is attributed to their chemical inertness and reluctance to participate in chemical bonding under normal conditions.

Key Concepts

Alpha Decay

Alpha decay is a type of radioactive decay where an unstable nucleus emits an alpha particle, which is the same as a helium nucleus, composed of two protons and two neutrons (\(^4_2 \text{He}\)). This process reduces the atomic number by two and the mass number by four.
During alpha decay:

• The parent nucleus loses two protons.
• Its atomic number decreases by 2, and its identity as an element changes.
• The mass number decreases by 4, due to the loss of two protons and two neutrons.

Alpha decay commonly occurs in heavy elements where the strong nuclear forces that hold the nucleus together cannot counteract the electromagnetic forces of repulsion between the protons.
It's an important concept in nuclear chemistry because it's a primary mode of decay for many heavy radioisotopes.

Nuclear Equations

Nuclear equations are used to represent nuclear reactions, such as the synthesis of new elements or radioactive decay. They are similar to chemical equations but focus on changes in the atomic nuclei.
Key points in writing nuclear equations:

• The sum of mass numbers (the top numbers) on the reactant side should equal the sum on the product side.
• The sum of atomic numbers (the bottom numbers) should also be equal on both sides.
• Nuclear equations often involve particles such as neutrons, protons, beta particles, and alpha particles.

In nuclear chemistry, it's crucial to balance these equations to understand the conservation of mass and charge during nuclear reactions. For example, the synthesis of element 118 involves a nuclear reaction between calcium and californium, which can be written and balanced to reflect the emission of neutrons.

Element Synthesis

Element synthesis refers to the creation of new elements, often in laboratories, through nuclear reactions. New elements are typically synthesized by bombarding a target nucleus with a "projectile" heavy ion.
The synthesis of element 118 involved:

• Colliding calcium-48 with californium-249.
• This process resulted in the formation of oganesson (element 118) and the emission of neutrons.
• Synthesis requires precise control over the energy involved to overcome repulsive forces between atomic nuclei.

These synthesized elements are usually radioactive and have short half-lives, but they expand our understanding of chemistry and physics, giving insight into the forces that hold atoms together and the limits of the periodic table.

Noble Gases

Noble gases make up Group 18 of the periodic table and are known for their remarkable stability. These elements have full valence electron shells, making them chemically inert.
Characteristics of noble gases:

• They are colorless, odorless, and tasteless.
• Noble gases include helium, neon, argon, krypton, xenon, and radon.
• Their inertness leads them to not easily form chemical compounds under normal conditions.

Oganesson, although a noble gas, may not exhibit typical noble gas behaviors due to relativistic effects influencing its electrons more significantly. However, understanding these elements provides insight into chemical reactivity and stability.

Periodic Table Groups

The periodic table is organized into groups, which are vertical columns that categorize elements with similar chemical properties. These groups reflect the elements' electron configuration, especially their outer shell structures.
Key aspects of periodic table groups:

• Groups are numbered from 1 to 18 on the modern periodic table.
• Elements in the same group often exhibit similar reactivity and bonding behavior.
• Group 18 contains the noble gases, renowned for their non-reactivity.

Understanding these groups helps chemists predict element reactions and properties. For example, the identification of oganesson in Group 18 aligns it with the noble gases, providing context for its predicted properties and behaviors.