Question

Concerning the incomplete seventh period of the periodic table, what should be the atomic number of the element (a) for which the filling of the \(6 d\) subshell is completed; (b) that should most closely resemble bismuth; (c) that should be a noble gas?

Short answer

The atomic number of the element where the 6d subshell is filled is 114. The element in the 8th period of group 15 that should resemble Bismuth should be 133. The noble gas in the 8th period of the periodic table should be 136.

Step-by-step solution

Identify atomic number of element where 6d subshell is completed

The first \(4 f\) electron is filled at atomic number 58, then 14 electrons in the \(4 f\) and then another 2 electrons in the \(5 d\) at atomic number 72. The \(6 p\) subshell starts after two more electrons are filled to \(5 d\) i.e. at atomic number 74. So, the \(6 d\) subshell begins at atomic number 104, after the \(5 f\) subshell is completed. As \(6 d\) takes 10 elements to fill up the d sublevel completely. Therefore, 104 + 10 = 114. Thus, atomic number of predicted element which completes \(6 d\) subshell should be 114.

Identify element resembling Bismuth

Bismuth is a member of group 15 and is in the 6th period of the Periodic Table. The element that most resembles Bismuth would be found two periods below; in other words, in the 8th period of the Table. The group 15 elements of the 7th period is Moscovium with atomic number 115. Thus, the group 15 elements of the 8th period should have the atomic number 115 + 18 (as there are 18 elements in a period) = 133.

Identify noble gas

Noble gases lie in Group 18 of the Periodic Table. The element of Group 18, in the 6th period, is Radon which has atomic number 86. The element of the same group in the 7th period should be element 86 + 32 (since there are 32 elements between the beginning of the 6th period and the beginning of the 7th period) = 118. Similarly, the element of the same group in the 8th period should be 118 + 18 = 136. This is the undiscovered noble gas of Period 8.

Key concepts

Atomic Number

The atomic number is an integral part of the periodic table, denoting the number of protons in the nucleus of an atom of an element. It's important because it defines the element, as each element has a unique atomic number. For instance, hydrogen, the first element, has an atomic number of 1, meaning it has one proton in its nucleus. This concept helps in understanding the arrangement of elements in the periodic table.

In the context of the incomplete seventh period, the atomic number also indicates when specific electron subshells start and finish filling. Generally speaking:

• The periodic table is built by progressively adding protons and electrons to the elements.
• This means each successive element has one more proton than the previous one.
• Hence, the atomic number increases consistently across the table.

When the 6d subshell is complete, it marks a point in the periodic table with a new atomic number. For example, the 6d subshell starts filling at atomic number 104 and is complete at 114.

6d Subshell

The term "6d subshell" refers to a specific set of orbitals within an electron shell. In basic atomic structure, electrons orbit the nucleus in regions called energy levels or shells, which are further divided into subshells. These subshells, designated by the letters s, p, d, and f, indicate the shape and number of orbitals they contain.

The 6d subshell is part of the sixth energy level, and electrons start filling these d orbitals after the fifth f subshell is complete, continuing the systematic progression:

• D subshells can accommodate up to 10 electrons in total.
• They begin filling after specific subshells - in this case, after the 5f subshell is complete at atomic number 103.
• Thus, the 6d subshell starts being populated starting from atomic number 104.
• When all orbitals in the 6d sublevel are filled, it marks atomic number 114 in the periodic table.

This is crucial to understanding the arrangement of electrons which define an element's properties.

Noble Gases

Noble gases are a group of elements known for their lack of chemical reactivity. These gases are present in Group 18 of the periodic table, characterized by full outer electron shells. This full valence shell configuration renders them largely inert, not engaging in chemical reactions under normal conditions.

Why are these gases important?

• They consist of elements like helium, neon, argon, krypton, xenon, and radon.
• Being inert, they are used in practical applications such as neon lights and helium balloons because they do not easily form compounds.
• In the periodic table, each noble gas represents the completion of a period.

Post radon, the next predicted noble gas is expected to have an atomic number 118, filling the 7th period. Continuing further, in an anticipated 8th period, the next noble gas is projected to possess atomic number 136, assuming the completion of a longer period sequence.